Engine over heating after highway speeds - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 5.3L V8 Engine and Drivetrain > Engine Tunes/Mods

Engine Tunes/Mods Performance Engine Tuning/Engine Modifications

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Old 06-17-2018, 11:40 AM
mysickTB mysickTB is offline
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2006 Chevy TrailBlazer LT
Summit White 5.3L V8 4X4
Join Date: Mar 2018
Location: Gainesville, TX
Posts: 6
Engine over heating after highway speeds

The engine overheating problem only occurs after driving at 55-70 MPH for 30-60 minutes. After the speed is reduced (to zero for a stop sign or stop/go traffic) the temp gauge in 10-15 seconds zooms from normal to 260 and the overheat icon is lit.
I have a new water pump, clutch and thermostat installed.
Engine compression is even at 180#.
The temp goes down if I increase speed above 40 MPH.
What would be the first step to identify this overheating issue?
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Old 06-17-2018, 04:25 PM
EnvoyBoy2004's Avatar
EnvoyBoy2004 EnvoyBoy2004 is offline
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2004 GMC Envoy SLT
Graphite Metallic 4.2L I6 4X4
Join Date: Sep 2014
Location: NY
Posts: 2,084
I would suspect air in the cooling system or a restricted radiator. Just my guess.
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Old 06-20-2018, 07:07 PM
rcf64 rcf64 is offline
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2002 GMC Envoy SLE XL
Sandalwood Metallic 4.2L I6 4X4
Join Date: Apr 2009
Location: SC PA (York/Gettysburg)
Posts: 2
I had this same situation earlier this spring. I have an 02 XL with the 4.2 engine.

I previously had the radiator, thermostat, and water pump replaced a couple of years ago due to a previous overheating condition. I left the coolant go too long before flushing and filling. Note - don't do that as the coolant gums up the radiator if you let it go too long.

So the engine was running fine at highway and stopped in traffic until this spring. Then I noticed the temp rising at low speed/stopped in traffic. It turns out the fan clutch was bad. I bought and installed a new fan clutch (the OEM AC Delco part). All is well again now.

When you said you replaced the clutch, I assume you meant the fan clutch? You'll know if it is working when the engine is hot because when you go to accelerate, it will sound like a jet engine under the hood. After you get up to enough speed to cool naturally, the clutch will disengage and quiet down the fan.

I would suggest revisiting the fan clutch.

BTW - the symptoms of the clogged radiator were the opposite - it overheated on the highway climbing mountains and towing a trailer. When I left off the gas going down hill, it cooled down.

Good luck...
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