Remove alternator to change Thermostat?

[mastermonkhabib]

So my 02 Envoy started throwing a code P0128 (Coolant Temp Below Thermostat Regulating Temp), so I figure its a bad thermostat. It also won't warm all the way up (fortunately we live in TX). So I go to my Chilton to make sure there are no surprises, I've changed them before on other cars. It say to remove the alternator. :eek: They look to be opposite sides. Anyone know a reason for this? ANyone else changed a stat on a 4.2L?

Thanks,
Donnie

[tahawus84]

well i cant help you with your problem, nut if that fixes the code code you let us know? My car has the same code right now thanks :)

[Dave]

Here you go guys! Long answer from Techline. Long story short, it does sound like the gen needs to be removed to get to the darn thing. R2 instructions are in the 2nd document.

Good Luck!

Dave

Document ID# 735601
2002 GMC Truck Envoy - 4WD


--------------------------------------------------------------------------------

DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions.

If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.

Conditions for Running the DTC
DTCs P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0325, P0336, P0420, P0440, P0442, P0446, P0452, P0453, P0480, P0502, P0503, for automatic transmission only, and P1441 are not set.
The engine has run more than 30 seconds and less than 20 minutes.
The minimum intake air temperature (IAT) is more than -7°C (19°F).
The engine coolant temperature at start up is less than 65°C (149°F).
Conditions for Setting the DTC
The average air flow is more than 20 g/s.
The vehicle has traveled more than 2.4 km (1.5 mi) over 40 km/h (25 mph).
Enough air flow has entered the engine and the engine coolant temperature has not risen to 80°C (176°F) for 30 seconds.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
Use a scan tool in order to clear the DTCs.
Diagnostic Aids
A DTC P0128 is designed to detect a faulty thermostat.
A skewed IAT sensor may cause this DTC to set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

This step tests for excessive resistance in the ECT circuit.

This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Step
Action
Values
Yes
No

Schematic Reference: Engine Controls Schematics

1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Is the cooling system low on coolant?
--
Go to Loss of Coolant in Engine Cooling
Go to Step 3

3
Turn OFF the ignition.
Disconnect the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .
Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor. Refer to Using Fused Jumper Wires in Wiring Systems.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the ECT sensor temperature.
Does the scan tool indicate that the ECT sensor temperature is more than the specified value?
138°C (280°F)
Go to Step 7
Go to Step 4

4
Turn OFF the ignition.
Disconnect the ECT sensor.
Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a known good ground.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the ECT sensor temperature.
Does the scan tool indicate that the ECT sensor temperature is more than the specified value?
138°C (280°F)
Go to Step 5
Go to Step 6

5
Test the ECT sensor low reference circuit for a high resistance or an open.
Repair the circuit as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 10
--

6
Test the ECT sensor signal circuit for a high resistance or for an open.
Repair the circuit as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 10
--

7
Remove the ECT sensor.
Suspend the ECT sensor and a thermometer in a pan of water.
Place the pan on a burner or hot plate.
Test the resistance of the ECT sensor through the specified range of temperatures.
Does the resistance and temperature closely match the Temperature vs Resistance table?
10-90°C (50-194°F)
Go to Step 8
Go to Step 9

8
Install the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .

Is the action complete?
--
Go to Engine Fails To Reach Normal Operating Temperature in Engine Cooling
--

9
Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .

Did you complete the replacement?
--
Go to Step 10
--

10
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 11
Go to Diagnostic Aids

11
With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK



--------------------------------------------------------------------------------
Document ID# 735601
2002 GMC Truck Envoy - 4WD

Document ID# 735499
2002 GMC Truck Envoy - 4WD


--------------------------------------------------------------------------------

Engine Coolant Temperature (ECT) Sensor Replacement
Removal Procedure

Notice
Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.


Turn the engine OFF.

Caution
Before servicing any electrical component, the ignition key must be in the OFF or LOCK position and all electrical loads must be OFF, unless instructed otherwise in these procedures. If a tool or equipment could easily come in contact with a live exposed electrical terminal, also disconnect the negative battery cable. Failure to follow these precautions may cause personal injury and/or damage to the vehicle or its components.


Disconnect the negative battery terminal.
Drain coolant below the level of the ECT sensor. Refer to Draining and Filling Cooling System in Engine Cooling.



Disconnect the ECT sensor electrical connector (1).
Remove the drive belt and the generator. Refer to Generator Replacement in Engine Electrical.



Carefully remove the ECT sensor (1).
Installation Procedure

Notice
Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.



Notice
Replacement components must be the correct part number for the application. Components requiring the use of the thread locking compound, lubricants, corrosion inhibitors, or sealants are identified in the service procedure. Some replacement components may come with these coatings already applied. Do not use these coatings on components unless specified. These coatings can affect the final torque, which may affect the operation of the component. Use the correct torque specification when installing components in order to avoid damage.


If installing the original sensor or a new sensor without sealant, apply thread sealer P/N 12346004 or equivalent.

Notice
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.






Install the ECT sensor. Tighten
Tighten the ECT sensor to 16 N·m (12 lb ft).





Connect the ECT electrical connector (1).
Install the generator and the drive belt. Refer to Generator Replacement in Engine Electrical.
Connect the negative battery terminal.
Refill the engine coolant. Refer to Draining and Filling Cooling System in Engine Cooling.

--------------------------------------------------------------------------------
Document ID# 735499
2002 GMC Truck Envoy - 4WD

[ghoster]

That was like the longest post ever.:rotfl:

[Dave]

Probably but it should answer their question and then some.

[ghoster]

I think if you read it all carefully, the meaning of life may be hidden in there somewhere!:rotfl:

[Dave]

Ha ha! Be glad I wasn't able to post the pics also.

[mastermonkhabib]

So from the tech doc, to replace the engine coolant temperature sensor, you have to remove the alternator. But for the thermostat I probably don't have to remove it. Otherwise, if I can do the work, worse case scenario, replaceing both will cost 20 bucks. I'll let you know how it went tomorrow.


And the meaning of life is for everyone to send me $20 by paypal. :m2:

[ieatglue]

I think if you read it all carefully, the meaning of life may be hidden in there somewhere!:rotfl:
:iagree: :laugh:

[ghoster]

So from the tech doc, to replace the engine coolant temperature sensor, you have to remove the alternator. But for the thermostat I probably don't have to remove it. Otherwise, if I can do the work, worse case scenario, replaceing both will cost 20 bucks. I'll let you know how it went tomorrow.


And the meaning of life is for everyone to send me $20 by paypal. :m2:

So thats the meaning of life......hey glue.....can you lend me $20?...thats in American money glue.:rotfl: :rotfl:

[Bulldog]

Reading instructions such as that makes even the backyard mechanic not even want to work on their toys.:undecided

[mastermonkhabib]

Reading instructions such as that makes even the backyard mechanic not even want to work on their toys.

I agree. I looked at the thermostat and have no Idea hot to get to the bolts, short of removing the power steering (which I don't want to do). And since my wife won't let me break her car, only my own, its off to the mechanic :cry:

[tblazed]

I agree. I looked at the thermostat and have no Idea hot to get to the bolts, short of removing the power steering ...

The thermostat is on the same side as the alternator. The GM service manual I have doesn't say anything about removing the alternator to get to the thermostat, but from the looks of it probably would make things easier to have it out of the way.

http://users3.ev1.net/~epadget/thermhous.jpg

[goes211]

It makes it rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrreeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaalllllllllllllllllllllllllllllllll easy. Sorry, didn't want to get caught with the shortest post.:rotfl:

[tahawus84]

Just wondering if you changed the t-stat and if it fixed that code? :hail:

[mastermonkhabib]

Just wondering if you changed the t-stat and if it fixed that code? :hail:

Finally changed it. I don't know if it fixed the code however. I live in Texas where there are only about a dozen days a year where it gets cold enough to throw the code, and those days are behind us. I did notice it took a while to warm up. I will be watching it over the next week or so to see if it warms up properly. I'm thinking it was stuck open, but was worried that one day it might get stuck closed (which doesn't work with 110 degree weather)

[Juiced_TB]

i had the same problem...t-stat was stuck open and was keeping the coolant at a low temp.

[bassman]

anyone know if thermostat is made into thermo housing . purchased thermo & seal from chev dealer looks nothing like original . maybe wrong part.

[MichEnvoyBoy]

anyone know if thermostat is made into thermo housing . purchased thermo & seal from chev dealer looks nothing like original . maybe wrong part.

I bought mine from the GMC dealer and it was identical to the OEM one. Are you sure you are looking at the t-stat, on the drivers side of the engine behind the alternator? I think a lot of people confuse it with the hose and housing on the passenger side of the engine behind the p-steering pump. That is not the t-stat.

If all is good, the t-stat should be identical to the OEM one thats on the truck. :yes:

[RozmerJJ]

This is what the thermostat should look like.

http://i137.photobucket.com/albums/q212/rozmerjj/Stat.jpg

[DC3843]

All,

My truck just threw this code today, but I live in El Paso where its blistering hot most of the time. Drove this morning and no problem, got in it at noon, and thats when the light came on. You think my t-stat is stuck open? The car is running a few notches below the middle of the temp guage. Thanks all.

[Blue03EXTLT]

I just replaced my thermostat today (P0128) code. If i didn't take my alternator out first there was no way in hell i was able to get at the hose and clamps. But alas after 4-5 hrs. and a hundred little cuts it is finished and working proper now.:woot:

[MichEnvoyBoy]

I just replaced my thermostat today (P0128) code. If i didn't take my alternator out first there was no way in hell i was able to get at the hose and clamps. But alas after 4-5 hrs. and a hundred little cuts it is finished and working proper now.:woot:


:eek:
You dont have to remove the alternator completely...

I removed the serpentine belt, took out the 3 bolts and was able to move the alternator slightly, thus helping me a ton get my ratchet, socket, and hands contorted into the fram :crazy:

IIRC, t-stat replacement on my '02 Voy took about 1hr.

[Blazernut]

So thats the meaning of life......hey glue.....can you lend me $20?...thats in American money glue.:rotfl: :rotfl:

Hmmmm American money ..... that's that dollar that is worth like 99 cents Canadian Eh? :dielaugh:

[iNetMANN]

Hmmmm American money ..... that's that dollar that is worth like 99 cents Canadian Eh? :dielaugh:


Wow, you're a real patient person having to wait 31 years to say that! :D

[rbarrios]

did you guys use the o-ring only?

How about the bolts?
Use any thread sealer stuff?

[henderbob]

So my 02 Envoy started throwing a code P0128 (Coolant Temp Below Thermostat Regulating Temp), so I figure its a bad thermostat. It also won't warm all the way up (fortunately we live in TX). So I go to my Chilton to make sure there are no surprises, I've changed them before on other cars. It say to remove the alternator. :eek: They look to be opposite sides. Anyone know a reason for this? ANyone else changed a stat on a 4.2L?

Thanks,
Donnie


I ran into the same thing, the manual has the alternator on the left side but my car has it on the right side. So what is involved to replace thermostat?

[henderbob]

I bought mine from the GMC dealer and it was identical to the OEM one. Are you sure you are looking at the t-stat, on the drivers side of the engine behind the alternator? I think a lot of people confuse it with the hose and housing on the passenger side of the engine behind the p-steering pump. That is not the t-stat.

If all is good, the t-stat should be identical to the OEM one thats on the truck. :yes:

Chilton's manual says to follow the top radiator hose to the block to find the thermostat. The hose goes behind the power steering pump which is on the passenger side of the engine. That used to be where the thermostat was always installed, where the upper radiator hose goes onto the engine. The lower hose goes to the area behind the alternator on my '03 Trailblazer.

[Super 88]

Chilton's manual says to follow the top radiator hose to the block to find the thermostat. The hose goes behind the power steering pump which is on the passenger side of the engine. That used to be where the thermostat was always installed, where the upper radiator hose goes onto the engine. The lower hose goes to the area behind the alternator on my '03 Trailblazer.
Then Chiltons is wrong. The thermostat is on the driver's side of the engine. The upper radiator hose goes to the passenger side of the engine. On these engines the lower hose goes to the thermostat.

[sctb]

Then Chiltons is wrong. The thermostat is on the driver's side of the engine. The upper radiator hose goes to the passenger side of the engine. On these engines the lower hose goes to the thermostat.

:iagree: Changed the t-stat on the last TB I had, it didn't help, actually began overheating instead of overcooling. But then it was a POS anyway with many other things wrong. I took the alternator out and it made it a simple job, but getting the alt out was anything but simple. One of the bolts comes out right into an a/c line and does not give you room to fully pull it out. After a lot of manipulation, I got it, then comes the experience of getting the alt out. Had to flip it over and angle it to get it out past the battery. Lot of time, lot of profanity, but was very easy to get to the t-stat after that. Some say go in through the driver's side wheelwell, but I can't see that being any easier, IMHO. Knock on whatever, the TB I have now runs dead on 210 and shows no signs of changing.

[91RS]

You can go through the wheel well to get to the thermostat, but I find it much easier to just remove the alternator because then it's right there and you don't have to fight anything.

[sheriff]

Just replaced the thermostat and also the second fan clutch (fun weekend) today. Anyways, all SES lights are now cleared and all seems right with the world. The one question that I have is the 'normal' op temp. From what I have read on here everyone seems to be running around 210F. Mine is currently around 192F, which makes perfect sense with the new 192F stat. Just looking for a little insite as to the reason why everyone else seems to run hotter normally and thinks it is AOK.:confused:

[Super 88]

Just replaced the thermostat and also the second fan clutch (fun weekend) today. Anyways, all SES lights are now cleared and all seems right with the world. The one question that I have is the 'normal' op temp. From what I have read on here everyone seems to be running around 210F. Mine is currently around 192F, which makes perfect sense with the new 192F stat. Just looking for a little insite as to the reason why everyone else seems to run hotter normally and thinks it is AOK.:confused:

Where did you get the 192F? From a scan tool?

The 210 we all reference is the dash gauge. The needle just stay right on the 210 mark.

[sheriff]

The 192F is from the dash gauge. That is of course an estimate of the reading but it is definately not 210F. Just curious more than anything. With all the work lately I wanted to make sure everything was good.

[Super 88]

J Mine is currently around 192F, which makes perfect sense with the new 192F stat. Just looking for a little insite as to the reason why everyone else seems to run hotter normally and thinks it is AOK.:confused:

Also, the thing to remember is the 192F of the new stat is the temp. that it STARTS to open, NOT the temp. that the engine will run.

You've said yours is not running at 210. I don't see how you could come up with 192 off the dash gauge. Is it one notch to the left of 210?

Check out this thread - especially post number 7

http://forums.trailvoy.com/showthread.php?t=49256&highlight=thermostat


Roadie along with others have stated that the 210 mark on the dash gauge can have a wide range of temp.

I bought my EXT new - it has always ran at the 210 mark (under normal driving conditions). I've rented SEVERAL of these vehicles over the years - they ALL ran at the 210 mark. All the rental vehicles (2004 - 2008) had less than 12K miles on them - some as few as 1,000.

[sheriff]

Thanks for the link to the other thread super88. The 192 was just an estimate. Yeah it is about one notch to the left of 210. All seems fine now. Just going to keep a closer eye on things for awhile.

[hazmatt24]

glad I read this thread before I tried doing this myself. The wife has her TB in the shop because of a transmission leak and I needed to change the thermostat on it but since it's already in the shop I'll just have the mechanic do it.

[stopher2]

Then Chiltons is wrong. The thermostat is on the driver's side of the engine. The upper radiator hose goes to the passenger side of the engine. On these engines the lower hose goes to the thermostat.


the v6 tstat is on the left side (driverside) of the car behind the alternator as you have asserted,....while

the v8 tstat is on the right side (passengerside) of the car down low as attached to the water pump.

i just tore up and replaced the waterpump, belts, tstat, clutch fan, but it didn't fix my hot engine problem. when running it cooled suddenly to good operating temp for 12 minutes, but got hot again.

i think that the coolant sensor is bad. where is this on the v8 ?

[KHill]

try a new thread stopher, might get some more traffic.

[rubberman]

i would avoid the autozone brand thermo, it hasnt been a year and the temp is reading lower and the idiot light is back on showing po128. Im gonna find a different brand this time around.

[pricelessone]

A friend of mine tells me the thermostat on my 4.2 liter in-line 6 in my 2005 Trailblazer 2wd LS is on the side of the block below the alternator on the lower radiator hose. I have the vehicle jacked up and felt around the housing which is attached to the block by what I believe at 100 mm bolts. I also noticed a "hump" on the upper side of the housing. Is this hump for "aligning" purposes when re-installing the housing? I have not removed the housing yet and being 68 years old and on Coumadin (a blood thinner) I want to avoid cutting myself. Should I remove the alternator to get to the upper bolt or can I get access to it from under the car? Any help would be greatly appreciated!:);):bonk::hail::thx

[the roadie]

Recommend removing the alternator for easier access. Of course, removing the alternator isn't trivial.

The hump is a small coolant bypass to make sure the thermostat sees the real temperature of circulating coolant. Otherwise it would just sit there stagnant and not moving.

Strongly recommend mechanics gloves for anybody with your issue. I just started wearing them at age 55 - they didn't exist when I was a kid.

Here's a pic.

http://info.rockauto.com/Gates/14659.jpg

[barniejekyl]

yes u have to remove the alternator.....some of the bolts are a search and find blind....but achievable.......not much room to work, but with a little patience, u can do it. this will be a good time to flush and change the coolant.....have fun....:cool:

[pricelessone]

Gonna go down to NAPA in morning and get me a 1/4" drive "wobbly" socket and get a new thermostat. I can see both bolts through the wheel well and think with a wobby 10 mm socket I can break them loose, with extensions, in the wheel well! Anyone ever tried that? I was told housing comes with a new thermostat, is this true? Is that just to make it cost more? Haven't checked on cost yet, anybody have an idea on cost? I am on a fixed income and like to plan ahead as much as possible! Gracias!:):cool:

[barniejekyl]

bought mine last week for 39.95...at a local auto parts joint.....roadie posted a picture of the assembly......it's exactly what i bought and installed.....good luck with the install.......

[pricelessone]

Found them in NAPA website and price is $32.39 and part number is THM 426190. The "O" ring is 99 cents and part number is FPG 35632 just in case someone else needs those numbers. Since I have an AZ resale certificate I might get it a bit cheaper than that.:D:cool::thx

[MAY03LT]

Anyone ever tried that?

Yuppers, there is a thread about it somewhere within these walls.

[pricelessone]

I have the Trailblazer jacked up and got the radiator hose loose at the radiator and didn't get too much of an anti-freeze bath (caught it in a bucket) and got the bottom bolt out of the T-state housing. Went to Sears and got a 1/4" drive swivel socket and used 2 long extensions and two short extensions attached to the swivel socket to get it out in the wheel well so I could take top bolt out but was never able to get that to work! So now I am taking the alternator off and got the top two bolts out but don't know where the 15 mm socket went when I took out back bolt. And, I assume, there is another bolt somewhere cause the alternator won't budge! Where is the 3rd bolt hiding?
Maybe I will find all that stuff tomorrow when I got some sunshine in the garage! Even had the wife out there helpin' me! That, in itself, earns me a gold star for today!:):eek::duh::bonk::cool:
P.S. Purchased new T-stat and housing at NAPA as I figured I would be getting a "quality" product, right? Came in a nice red, white and blue box and when I got it home and took it out of the box, cast into the housing was the "DFT CHINA"! The T-State has 86 degrees centigrade stamped on it which would make it about 183 degrees farenheit for what that's worth!

[WOOLUF1952]

Probably too late now, but don't they call for a 192 degree t-stat? Keep an eye on your temp gauge to see if it is reading @ 210.

[MAY03LT]

Where is the 3rd bolt hiding?


Two bolts on the top of the alt case, one on the bottom.

[ReconDrill]

This is a very informative thread. My TB hit trouble code P0128...not sure what to replace first...guys at parts store wanted to sell me temp sensor ($27) and a thermostat costs $24. With the definition of this DTC as: low coolant, bad thermostat or faulty thermostat control sensor.

I went cheap and replace radiator cap and re-cleaned throttle body, just for the heck of it (had some carbon build up. Just cleaned the darn thing 4 months ago.

Also got some good advice about cleaning the MAF to possibly reduce a hesitation problem.

Aftering consulting with the TB driver (my wife), the temp guage stays just below 210...I now believe the thermostat may be a bit faulty. It this code pops up again, a new thermostat will be installed (behind the alternator).

Again...very informative thread!!!

[sirjorge]

Yeah, I've got the same code and the same problem. I am thinking about tackling it this weekend.

I've noticed it seems to be TX TVs with this issue. Does the excessive heat cause the thermostats to go out? If it was just heat, I would think that AZ or another hot desert area would claim more.

[Bob G]

Just replaced the t-stat on my 03 TB 6L and not sure how you can do this without removing the alternator. Tried, but couldn't do it!

[ReconDrill]

SES light came back on...had to replace thermostat. Took 3 hours, did not have to remove alternator...just removed both top bolts and loosened bottom bolt. Was able to get to top thermostat housing bold, throught the DVR side wheel well and a few rachet extensions.

Lost one thermostat housing bolt, after a quick trip to NAPA, got a suitable replacement. Now my temp gauge reads right at 208-210.

Funny thing, after complete assembly and test drive, the orginial thermostat housing bold appeared...now I have a spare :) :duh:

[mikeyslacker]

My 04 TB is kicking back a code of P0128. Decided to change the Thermostat, just seen a post mentioning that the Thermostat marked 86C is not the correct. IS this true? Does anyone have any input on this. I just need to pass inspection already.

[WOOLUF1952]

86C is only 187F. I believe that's too low. 89C = 192F, which is what our trucks call for.:m2: Others will jump in.

[mikeyslacker]

great thanks for your help! Now I have to go back to the store and tell the clerk that he gave me the wrong thermostat, this should be fun, trying to reason with someone who will not understand a word that I am saying.

[Rodgers]

I have a 2004 envoy 4WD 179,000 miles, we (my husband and myself) changed the thermostat yesterday. We could not have done it without removing the alt. even with my small hands. I think that the A/C was the biggest problem, too many hoses in the way. By using this site we have been able to change our spark plugs, clean the throttle body, replace the brakes and 02 sensors. I am still getting a misfire code on the number 3, replaced the coil on thanksgiving. When I replaced the plugs I got Bosch, I am thinking about changing them again. I love working on my car and don't have to feel like I am getting it from Pepboys. Thanks again!

[the roadie]

Bosch plugs and O2 sensors haven't has as a consistently good reports back as AC Delco. Use 41-103 iridium plugs.

[Beau57]

Just replaced my thermostat yesterday, read this post and looked at the pictures for a plan of attack. I had a code P0128 also with temps running in the low 170's. I studied the left wheel well access to the stat and concluded I didn't have enough tools (extensions) to reach but could see how it is very do-able. I was very aware of the dropping a bolt issue and had my trusty antenna like telescopic magnet which proved to be a valuabled addition to the project, I had bought it at Harbor Freight for $1 and used it four times. I used a 1/4 inch drive ratchet on the thermostat 10mm bolts due to the tight space. I would suggest using a swivel adapter before the socket because of the less than straight on approach to the bolt heads. Total time was just over two hours so it appears I was right on with others doing this job. I had a very limited timeframe to perform the job and was worried I would run into some type of unforseen problem that would prevent it's completion on a Sunday afternoon. This is one of those jobs that just cannot be done quickly no matter how prepared you are going in. If I had to do it again I think I could safely save 30 minutes due to the experience gained. Took it for a test run afterward of 10 miles or so. Highest temp attained now is the width of the temp guage needle less than 210deg. So maybe 200-205? The thermostat itself is 190deg and allowing for the time lag of operation seems to be working correctly. I now am anticipating a slight increase in mileage numbers. I got the code P0128 driving it home the day I bought it. I did a scan and realized it was nothing serious, of course the wife thought I was being ripped off. So for the life of my ownership I have seen the "SES" light and it has run more rich due to the low temps. It took me a month to get to the job and must admit saving a couple hundred bucks was very satisfying. I had whine coming from the engine that I tackled at the same time. I replaced the idler pulley. By itself it is a very easy fix. I got rid of almost all the whine. I suspect the tensioner pulley needs replacing also as I have a small amount of the same type of whine left over. I was told by my parts guy that the tensioner pulley uses the same part # as the idler pulley for the pulley itself and not the tensioner assembly, if so this would also be an economical fix.
This was my first post. I would like to thank all that have contributed to this site as it makes our jobs easier. I hope my experience helps.....Beau

[nhserrano]

I am a graphics understanding guy... so, Could someone upload some pics about how to replace the thermostat, I really appreciatte it:undecided:undecided!!!

[the roadie]

You might find the Haynes manual a great help.

[aldaran]

My uncle's TB is throwing this code and I plan to tackle the job of replacing his stat next weekend. He has a 2005 Inline-6, so the stat is on the driver's side and not on the passenger side? All my other Chevrolet vehicles had them where ever the top radiator hose went. Thanks for you replies.

[lynch55]

This ain't your granddaddys six cylinder! That thing is on the bottom hose behind the alternator! I changed mine by removing the drivers side front wheel and useing long extentions to get to the bolts. Didn't take long at all! Still disconnected the neg. battery terminal as I was worried about shorting out with exts. Took about 20-25 mins. Good Luck which ever way you decide to do it!

[Rodgers]

Yes, on the driver's side behind the alternator. The job itself is not that bad, but due to access problems it can be time consuming, so I would allow 4-5 hours. The A/C hoses created the biggest obstacle for us, you just have to gently move them out of your way.

[aldaran]

I will try the alternator way first. If that causes issues, then it's the wheel well way. Once again thanks for the info. You guys are great.

[KNBlazer]

the v6 tstat is on the left side (driverside) of the car behind the alternator as you have asserted,....while

the v8 tstat is on the right side (passengerside) of the car down low as attached to the water pump.

i just tore up and replaced the waterpump, belts, tstat, clutch fan, but it didn't fix my hot engine problem. when running it cooled suddenly to good operating temp for 12 minutes, but got hot again.

i think that the coolant sensor is bad. where is this on the v8 ?



If you have a 2003 TB and you haven't replaced the fan clutch recently from the dealer, then you may be required to change the clutch to the updated part number as well as get the new calibration for the ECM... many members have had this problem in the past, myself included...

[aldaran]

Well I got it done. It was much easier to go through the wheel well with a long extension. Of course I needed a swivel to get the top bolt off. Another handy item was a magnetic antenna in case you drop the bolt when putting them back on. This happened about three times to me when doing the top bolt. With all the right tools on hand it took about 1 hour. Thanks for all the replies!

[fred2004]

My TB was doing the DAILY code last year.
It seems to have corrected itself, though.:woot:

[havrelm1]

05 TB 4.2:

I tried removing the alternator, no dice, the AC line is right in it's way directly in line with the center of the bolt, could not move it any direction at all without bending the hell out of it and risk damaging it, the joint would start to flex at the condensor, couldn't get a hold of it at the bottom, didn't want to mess with it, will have to try the wheel well method. Maybe my AC line was bent some when the vehicle was manufactured, no way it was moving to get a socket in there without some excessive force.

I have plenty of experience too, and after 2 hours and no progress, I'm done trying to remove the alternator to replace the tstat.

Looks like I'm doing my 6 hour drive to LA from Phoenix with the engine running a little cool and with the CEL on! I don't have any more time right now to F with it.

[lynch55]

:m2:I tell you, 45-60 minutes and long ext. and swivell and telescoping magnet, and you're done!:thumbsup:

[91RS]

05 TB 4.2:

I tried removing the alternator, no dice, the AC line is right in it's way directly in line with the center of the bolt, could not move it any direction at all without bending the hell out of it and risk damaging it, the joint would start to flex at the condensor, couldn't get a hold of it at the bottom, didn't want to mess with it, will have to try the wheel well method. Maybe my AC line was bent some when the vehicle was manufactured, no way it was moving to get a socket in there without some excessive force.

I have plenty of experience too, and after 2 hours and no progress, I'm done trying to remove the alternator to replace the tstat.

Looks like I'm doing my 6 hour drive to LA from Phoenix with the engine running a little cool and with the CEL on! I don't have any more time right now to F with it.

You can't get a socket on that bolt, you have to use a wrench (ratcheting box end works best).