Replacing Thermostat For The Cooling System on a 2008 Chevrolet Express 1500

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This procedure works for the GMC Savana as well from years 1996 to 2016. This applies to all v6 engines from all years and early v8 models before 2002. How to replace the thermostat from check engine code p0128. If you get this code it can be any of the three possible things, the coolant is old and no longer is keeping the engine within operating temperature. The thermostat has gone bad, or the sensor that reads the thermostat has failed. To figure out which of these it might be some detective work is needed, if you just replaced the coolant within the last 5 years or 100,000 miles, then the coolant might not be the suspect you should be looking at. The engine doesn't warm up to operating temp or sometimes the cluster in the car reads or doesn't read the temp then it could possibly be the thermostat being stuck open or the sensor reading the thermostat. If the car is constantly on the verge of over heating then it could be the thermostat if you have already ruled out the coolant. Lastly is the sensor, the the cluster is reading a signal and the gauge is working, and you have tested the thermostat spring to make sure it is working correctly then you know its the sensor. This guide is on how to replace the thermostat, refill the coolant, and bleed the system.

  • Rachet 1/4 drive
  • wobble extension of 6 inches
  • appropriate sockets
  • flathead screw driver
  • drain pan
  • towels or rags
  • funnel
  • jack and jack stands or ramps
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  • dex cool coolant a few quarts at least
  • New Thermostat like Duralast #15119 or AC Delco #12632948
  • A new rubber seal if new thermostat doesn't come with one.
  • blue gasket sealant

Gaining access to the thermostat


First remove the air filter housing assembly, its held in by 2 bolts and a fastening clamp that is at the beginning of the hose duct.

There is no need to remove the MAF sensor we just need to move the assembly out of the way, Do not disconnect the MAF!

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Now to remove the air duct to the throttle body, follow the duct to the back of the engine bay, right above the thermostat housing is where the fastening clamp is, the flat head screw should be easily accessible, use the flat head screw driver and unscrew the fastening clamp and then suggestively pull the duct off.

The hose wiggles off with a bit of force, don't use a pry bar or anything that can mar or tear the duct, its easily breakable.


Having removed the duct you should now see the thermostat housing, if you follow the upper radiator hose into where a metal elbow is, this is the housing. It is held in by 2 bolts. The bolts sit diagonal from each other.

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this is where a wobble extension comes in handy as there are many hoses and things reducing room for activities

Image 8106 from Replacing thermostat for the cooling system on a 2008 Chevrolet Express 1500

Unless you have a OEM thermostat from Chevrolet or GMC the seal that comes with the thermostat most likely won't fit properly, so use the blue gasket maker sealant to make a new seal. The spring end of the thermostat goes into the engine with the top of the thermostat butted against the top of the thermostat housing.


Install the new thermostat and then hand tight the bolts, top off the radiator to make up for the lost coolant when the thermostat was replaced.

keep the radiator cap off to help relieve any trapped air in the system, best to do this on an incline or with front of the van jacked up or on ramps.


Turn the car on and let the engine warm up, carefully watch the temp gauge and make sure you are reading a temp for the engine. As long as the engine isn't overheating and warming up the thermostat is working correctly


Check for leaks, if there are no leaks, torque down the thermostat housing bolts to 18 Ft-Lbs. Reattach the air duct and the air filter housing.

Watch the temp gauge carefully for a few drives and make sure the car doesn't get close to over heating, if it does you have trapped air in the cooling system and need to bleed out the air or you did not install the thermostat properly and or the thermostat has failed again.

Thermostat housing bolts torque value is 18 FT-LBS

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