Failing Thermostat?

[Delta]

So recently with it getting cooler the truck is not warming up like it should or staying where it used to. This is about a 20 minute ride around town: Normally it would be at the notch right before 210. Was that way last winter. The odd thing is I do have heat, although I don't think it is as warm as it once was. Upper radiator hose is warm, but not hot. Lower is barely warm enough to tell. Clutch fan seems to operate as normal. Could this be a sign the thermostat is going out, or something else?

 

[Nick1994]

Probably a bad thermostat. My grandparent's Trailblazer did the same thing. Do you have a code reader? Or know someone with one? If so, plug it in and see what the computer says the temperature is, sometimes those gauges aren't that accurate. Also, OEM thermostat or nothing. We had a Stant put into their Trailblazer and it started running hot, Stant replaced with another Stant still running hot. Then got an OEM and it was a lot better. Turned out the Stant had a smaller opening that the OEM, we used a micrometer and it was somewhere around a 10-12% smaller opening.

 

[WobblyElvis]

Most likely the thermostat. As Nick said I would consider an OEM unit. The quality of the aftermarket parts has taken a nose dive.

 

[StevieC]

Thermostat. Surprised the ECU hasn't set a code for the engine not reaching operating temperature.

 

[Nyquist]

Originally Posted By: Delta

So recently with it getting cooler the truck is not warming up like it should or staying where it used to. This is about a 20 minute ride around town: Normally it would be at the notch right before 210. Was that way last winter. The odd thing is I do have heat, although I don't think it is as warm as it once was. Upper radiator hose is warm, but not hot. Lower is barely warm enough to tell. Clutch fan seems to operate as normal. Could this be a sign the thermostat is going out, or something else?

As others have said, the thermostat is probably partially stuck open. I had this on our Cobalt, and the symptoms were similar. It would only allow the engine to reach a temperature of 168F on the open road. I would swap it out before it does move again and gets stuck in a completely closed position and will not open which would cause over-heating. As for the CEL, it will only illuminate that if the PCM cannot reach a closed loop condition. For some engines, that is as low or lower than 120F.

 

[92saturnsl2]

Most modern GM vehicles will set a P0128 if the coolant temp is low, or not reaching operating temp fast enough. I believe the trigger is around 160-170F, and x number of minutes to reach it. I can easily set the code by installing a 160*F thermostat, whereas a 180F won't set it. You should plug in a scanner and see what the actual coolant temp is. Torque app and cellphone/bluetooth adapter is an easy method. Many GM vehicles have a separate coolant temperature sensor for the gauge and ECU. If you replace the thermostat and that doesn't change the temperature reported, I would look at the coolant temperature sensor. They are cheap and usually easy to replace.

 

[Delta]

Thanks for the replies. I've had a sneaking suspicion the engine isn't getting warm enough, you'll notice the oil pressure sits higher than it used to. I'll get the parts tomorrow. Probably will get new hoses while the coolant is drained. If it isn't the issue it's preventative maintenance anyways.

 

[Garak]

I would change it out. From the vintage of your truck, it looks like you're fortunate enough to have a GM of the vintage where the temperature gauges were actually very useful at discerning stuff like this. On second thought, that truck is a ticking time bomb with that thermostat. Bring it up here, I'll take the risk and take it off your hands.

 

[Delta]

Originally Posted By: Garak

On second thought, that truck is a ticking time bomb with that thermostat. Bring it up here, I'll take the risk and take it off your hands.

Anything's possible for the right price A 2wd 4 cylinder S10 would not do very well in Canadian winters, lol.

 

[2strokeNorthstar]

I wonder if those temp gauges work on Chevys. Most cars since the 80s-90s just show 1/2 way from about 170-220. They don't mean much.

 

[Garak]

Originally Posted By: Delta

A 2wd 4 cylinder S10 would not do very well in Canadian winters, lol.

You'd be surprised. I throw my tractor wheel weights in the back of the F-150, and it's fine with two wheel drive. Some years ago, a buddy and I were going up a snow covered hill, with remarkably the same tires, two wheel drive, he had a GM and I had my Ford. He couldn't understand how I got up so easily when he was struggling with it. Over 300 lb of weight over the rear axle helped, I guess.

 

[Garak]

On the GMs I had experience with, they worked until around this generation of truck, at least. You could actually see when the thermostat cycled or the electric fan kicked in while sitting and idling.

 

[Delta]

Originally Posted By: Garak

On the GMs I had experience with, they worked until around this generation of truck, at least. You could actually see when the thermostat cycled or the electric fan kicked in while sitting and idling.

Yup, especially the voltage one. During high electrical loads it will move around a bit. The temp gauge will normally move to the 210 range going up the mountain at high RPM's. Have to keep the revs up or you're in for a bad time

 

[Garak]

You could see all kinds of nifty things when the cabs first got electric fans.

 

[Delta]

Update: Assuming the typical Chevy position (joking, been a good little truck!). Replaced the thermostat and hoses a couple hours ago. Did not change the temperature gauge reading, but I did notice the hoses were original (dated September 1998 ) and the heat was noticeably warmer afterwards. Went and replaced the coolant temp sensor as well. It probably needed a coolant refresh anyways so it was all needed in hindsight. Don't know if its ever had a coolant change, but it drained fairly clean with only staining on the housing. Here's a temp reading from the heat, seems nice and toasty now.

 

[Garak]

Yes, that stuff likely was more than due to be replaced, and nice to get it in order before the weather gets worse.