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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Engine Tunes/Mods

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Old 04-10-2019, 10:35 PM
medicmandan medicmandan is offline
New Member
2005 Chevy TrailBlazer LS
Summit White 4.2L I6 AWD
Join Date: Jan 2017
Location: Utah
Posts: 9
Originally Posted by Atoy View Post
These vehicles have the terrible electronic fan clutch that apparently was so troublesome that GM abandoned it and went back to a mechanical fan in 2008.

My 2004 TB will not pull a small camper in weather above 80 degrees without overheating and I tried almost everything, including a overhaul of the entire cooling system and exhaust. The only fix that finally worked was a Fan override that requires bypassing the computer to force the fan to run full speed.
Someone said they put a 2008 mechanical clutch on the 04 and it worked. I have not tried that one.
I have similar issues since I put in a transmission cooler. If it is above 80 and I am not moving the temp goes up. New radiator, water pump, thermostat, temp sensor, fan clutch and hoses. Turn the AC off and it helps but the temp still stays higher than normal until I get moving again.

The trans cooler is not blocking that much of the radiator but it must be just enough to reduce the airflow. I suspect there is a computer problem that is not triggering the fan to increase speed. I had one shop check it out but their scanner would only say it was operating at the right speed at idle (700rpm I think).
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Old 04-16-2019, 08:02 AM
45Frank 45Frank is offline
Junior Member
2003 GMC Envoy SLT XL
Carbon Metallic 4.2L I6 4X4
Join Date: Sep 2018
Location: WNC
Posts: 65
Folks if ya go lok at my thread I had a fan clutch issue. I installed two different ones and it still didn't work.
Ended up at the dealer where I was told the aftermarket clutches don't always work because of different computer issues.
They replaced my Clutch with a GM, new relay and HAD to reflash the computer at the cost of $1,300.00. It works good now for a few months and I have read on other forums the same story. Some after market clutches do not recognize the computer. Sucked for sure.
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