Proper thermostat operation

[littleblazer]

Hey guys. Been busy and thus haven't been around too much the last month or so. Got a lot going on. Anyway I have a question regarding the correct operation of the thermostat on our trucks as I for really know how out system is supposed to work. Here's the story:

Last week or two weeks ago I opened the hood on my truck to top off the washer fluid. I figured I'd let the truck warm up while I was doing that so I started it. Note it had sat in the driveway for a few days since it last ran. At any rate it ran for a minute or two and as I leaned over I felt that the upper radiator hose was warm. Not hot but warmer than air temp which was around 70. Then I felt the end cap and same thing it was warmish. Check the cluster and sure enough it's reading maybe 130. Now it wasn't that warm but warm. Long story short in the winter I experience long warm up times. Like if I were to let it idle in my driveway for 20 minutes it won't go over 170 warm but in the summer it behaves as normal albeit a little hot at times. (It'll jump to 235 and I do have a thermal clutch, at that point it is locked solid) I guess what I'm asking is if there is a bypass built into either the thermostat or water pump that allows for some coolant exchange when the thermostat is closed or am I dealing with a slightly stuck stat...

Based on more traditional cooling systems I've worked on I tend to believe it's a bad or junk stat.

 

[Sparky]

Depending on outside temp I could see 20 minutes of idle not getting it to 210 just because idle won't warm up overly fast. That said, I had not timed mine to say for sure.

 

[littleblazer]

Let us say it was like 40s. Even if it was warm and I run into a store and it cools off to 160 by the time I get back in and start it if it were to just idle it wouldn't get back up to temp either. Other thing I noticed is on a cold night wot on an onramp to 65-70 to get on the highway will drop it into the 180s. But we're taking 20 ambient. I know on boats at wide open the thermostat will blow open so I don't know if that's normal on these as well.

 

[Mike534x]

It sounds to me like your thermostat is starting to go bad. On my first Envoy, the first sign was the temperature fluctuations. I also noticed that as it got colder out, the slower it was to warm up to operating temp....that was with driving it 20 minutes and a mix of traffic on the way to school. The highest it would go was about 170-180, then it would drop to 120-140 if I started to drive. Fuel ups noticeably increased, stopping twice a week instead of once. It also didn't help that the computer kept kicking the RPM's up to "warm up" the engine, despite it being well into the drive as if it was a cold start overnight. I drove it for about half the winter like this, until I stumbled upon the OS where I learned what the culprit was. It never threw a CEL either, despite it running rich and never reaching operating temperature.

I hardly ever see the temp gauge fluctuate if any, its always usually pointing straight up on 210, or a small hair off.

 

[Matt]

Also remember that our 4.2's are a reverse flow system, not a "normal" flow like the majority of vehicles.

I'm guessing you're running an app or something to read real temps?

I'm with Mike, sounds like it's starting to stick open.

 

[littleblazer]

Well that's the other thing, it's been like this since I started driving 5 years ago. Hasn't gotten any worse. But it sounds like I'm adding thermostat to my to do list. Probably flush the system out while I'm in there.

 

[NJTB]

Mine did the same thing. I put in a new thermostat and for a few years (3) it ran in the 200-210 range. I checked it the other day and it's running 190-196. OK but not great, I'll probably put a new thermostat in soon.

 

[IHZ05VOY]

Just ordered another t-stat. Seems like I replaced yesterday . lol My temp ranges from 170-180 even after running 10+ mins. Check engine light came on, but it went away a few months back. Finally came on again today and I had enough. Ill be busy this weekend.

 

[littleblazer]

So since my alternator died I guess it's a good time to slap in a thermostat right? I'm going to guess Delco only on these. Seems like people have issues with aftermarket if I remember correctly.

 

[Mooseman]

I got better results from ACDelco t-stats. Better temperatures.

 

[Matt]

Yep, I did the replacement yesterday....2 hours because of the bottom alternator and thermostat bolts. But, I went with a Delco this time and the temps are where they should be now. You'll need 10mm and 15mm sockets, wrenches and a 15mm stubby for the bottom alt bolt if you don't come in through the wheel well with a long arse extension.

 

[littleblazer]

Yep, I did the replacement yesterday....2 hours because of the bottom alternator and thermostat bolts. But, I went with a Delco this time and the temps are where they should be now. You'll need 10mm and 15mm sockets, wrenches and a 15mm stubby for the bottom alt bolt if you don't come in through the wheel well with a long arse extension.

I actually got by with a quarter inch ratchet on the bottom bolt. Was able to use a 3/8 shallow with a 3/8 to quarter inch adapter.

 

[Locksmith]

Well that's the other thing, it's been like this since I started driving 5 years ago. Hasn't gotten any worse. But it sounds like I'm adding thermostat to my to do list. Probably flush the system out while I'm in there.

I'd replace the coolant temperature sensor while you're at it. It's right next to the thermostat.