This article comes about by the seemingly mass confusion of where the thermostat is located on 2002 and up Chevrolet Trailblazer, GMC Envoy and similar body styles with the 4.2 liter inline six cylinder engine. I’ve seen many times, in person and online, people claiming the thermostat is on the right (passenger) side of the engine, inside a small housing that looks very similar to the V6 engines. This is NOT the case at all, and people that do not know what they are talking about can be misleading the regular guy trying to fix his vehicle.
On earlier model vehicles, and even the S-series Blazer that was still out when the new body style Trailblazer came out, they had a V6 engine with the thermostat located right in the front, on top of the intake, just about dead center of the engine. When the inline six engine came out in 2002, the thermostat was re-located to the left (drivers) side of the engine, behind and a bit below of the alternator. The housing and hose that is now on the right side of the engine is just an inlet housing for the coolant. There is NO thermostat inside that housing.
As you can see in the provided pictures below, the thermostat is an integral part of the outlet housing, and is NOT serviced separately. You CANNOT just go to the parts store and get a thermostat in a box. This unit needs to be replaced as a whole. The repair can be made through accessing the bolts to the housing through the left front wheel well opening, or if you prefer, the belt, and alternator can be removed, but that is a bit more work.
I really hope this clears up any confusion you may have heard elsewhere. When it comes to a situation like this, you really need the correct information from someone who does this for a living!
Do i need to purge cooling system on 2004 envoy after draining cooling system
ProTech:
After refilling the radiator, let the truck run for a while with the cap off. It should bleed out any air easily that way. You may have to top off once the thermostat opens, but probably not that much. Once it’s hot, and circulating, put the radiator cap back on and you’ll be good to go.
Great pictures Protech. I read on forums all the time people saying the thermostat is in the upper radiator hose- which it is not. Maybe now they will see this article and put the argument to rest ! That part is hard to replace. Antifreeze gets all over the place and one of the bolts is a a pain to remove.
You’re the graetset! JMHO
Sorry to say but my 2004 has the thermostat located on passenger side of block near power sterring pump. Trying to figure out how to get out and find right part.
That’s where I thought it was located too. Let me know how it goes and how to replace it. A picture of the thermostat when you do it would be great too !
You really saved me some money with this information. Thanks!
If what you are saying is true and that the vortec inline 6 has no coolant temp. sensor then why does auto zone sell one ?Duralast/Coolant Temperature Sensor
For your 2004 GMC Truck Envoy 4WD 4.2L SFI DOHC 6cyl
Price: $29.99
Please help before i spend my money
Who said there is no temperature sensor? All I see talking about is the thermostat location, not any temp sensor?
the link that brought me here says there is no coolant temp. sensor see thermostat
http://greatautohelp.com/sensor-location/4200.html
Quote 04 GMC envoy 4.2L can you tell me where is can find coolant below temperature sensor.
There is no such sensor. I am guessing that you have a
check engine light with code P0128- coolant temp below
thermostat regulating temperature. This code is cause by
either low coolant level, or more likely- a bad thermostat.
Yes. If you read the sentence of the page your just posted, it says- where can I find the “Coolant Below Temperature Sensor”. There is no sensor called that. There is however a “Coolant Temperature Sensor”.
Changed thermostat today . What a Mother %$%%$$ to get to! also changed belt while alt. was off thanks for the help. Peace out and Merry Christmas !
This sounds like the the radiator may have had an air pocket and needs the coolant topped off. Also may need to replace the tiadaror cap as the system needs to be able to build pressure. Worse cause would be a blown head gasket but you would notice a loss of coolant in the tiadaror.
What tools do I need to replace my thermostat on a 2005 trailblazer trying to do it my self and any of you guy have a problem with a number 5 cylinder miss I replace spark plug,coil pack and rubber boot or spark plug wire and it still missing help
You just need a 10mm socket on a long extension and jhose clamp pliers. Get to the bolts through the drivers side wheel well opening.
Nice article and clarification on 4.2L I6 Trlblzr,GMC,Envoy;Several emails & mechs. have put articles for DIYs out there w/incorrect info…its not one text book proceedure fits all..appreciate those of us actually work on these vehicles putting accurate articles with pixs or diagrams as yours…keep em running brother!!!
so I tried goig through the wheel well (had to buy an extension) but the top bolt is behind the alternator, how did others get to that bolt?
Use a universal joint or even better a wobble end extension. That will give you enough angle to get that bolt to remove the thermostat housing.