C5 confusion

"PartyPooper2012" (PartyPooper2012) 04/08/2020 at 12:15 • Filed to: None

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Last few non winter months I drove my C5 and coolant temp would get up to and stay around 190-210 F.

This spring I dug out this mystery machine and coolant temp gets up to and stays around 160-180 F

Do we think thermostat is stuck open or is this normal behavior considering outside temps are cooler ? Temps outside have been in 50s and 60s where as during previous times, temps outside have been summer temps - 75-105

I get the fact that it’s cooler out, but gasoline burns and makes heat so car should run around same temp all the time. After all, when it’s stupid freezing outside, my other car doesn’t operate at negative temp

jimz > PartyPooper2012 04/08/2020 at 12:22

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possible.  my Ranger did that a couple of years ago.  Temp gauge just progressively read lower and lower until the CEL finally lit up. 

PartyPooper2012 > jimz 04/08/2020 at 12:23

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What did the error code say? Warm up your car to continue? 

jimz > PartyPooper2012 04/08/2020 at 12:35

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P0128 - Coolant Temperature Below Thermostat Regulating Temperature

atfsgeoff > PartyPooper2012 04/08/2020 at 12:36

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Could be the t-stat is stuck in a partially closed position, just enough to have a gradient engine temp depending on ambient temp. With a properly functioning thermostat, the operating temp of the engine shouldn’t waver more than 5-10 degrees whether it’s 10F or 100F outside.

PartyPooper2012 > atfsgeoff 04/08/2020 at 12:39

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Hmmm. Now I got some wrenching to do.... or do I leave it be? Car running cooler. What’s the down side here?

Highlander-Datsuns are Forever > PartyPooper2012 04/08/2020 at 12:41

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My bet is the T-stat is stuck open. Try driving it down a hill after a full warm up in gear and see if the temp significantly lowers. 

PartyPooper2012 > Highlander-Datsuns are Forever 04/08/2020 at 12:43

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so many questions.

1 - why

2 - how long a hill?

3 - how fast do you think coolant will change temp?

I gave it some spirited driving this morning and temp stayed same. 

XJDano > PartyPooper2012 04/08/2020 at 12:44

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Similar thing with our van, it was only reading 165° during the winter and the gauge was 1/4 of the way, 1/2 is normal temp. I put it off for a while, then eventually changed thermostat and it was right at normal temp after.

It’s likely needing a new thermostat. 

Snuze: Needs another Swede > PartyPooper2012 04/08/2020 at 12:49

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For what it’s worth the combustion temperature does vary with the outside air temperature. But it’s so much higher than outside air temp that it doesn’t matter much . In other words the car should have a higher coolant temp when it’s 100F vs. 0F, but not 100 degrees higher. It should be more like a 10-20 degree difference (probably). If you’re seeing a nominal 30F reduction in coolant temp for a similar 30 degree reduction in outside air temp, me thinks your thermostat is going bad, or something.

One thing to consider - how long have your drives been and what kind of driving have you been doing? My understanding is most GM vehicles (not sure about other manufactures, but this seems to be mostly a GM thing from what I’ve read) use a thermostat system with a small bypass, meaning the thermostat is never truly “shut”. They do this so that the cars can provide a little heat, faster, in the winter time, and as protection for the engines against a thermostat that fails shut (unlikely but could happen ). The reason I have become familiar with this is the Cruze TAKES FOR F!#$%kING EVER TO HEAT UP when I’m commuting in the winter . I drive 14 miles to work, on some hilly, but slow roads, usually not getting up more than about 40 MPH,and often in stop/go traffic. The car is a stick so it also has DFCO (deceleration fuel cutoff). If it’s below about 23F the car will not make any appreciable heat before I get to work. So if you’re doing a lot of relatively short, light load drives, it is possible you just aren’t heating it up enough. 

Highlander-Datsuns are Forever > PartyPooper2012 04/08/2020 at 12:49

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If your engine rapidly cools down when going down a hill with very little fuel going into engine it is a good indicator the t-stat is stuck open, it should in theory close and kind of maintain temp. I had a stuck t-stat on my mazda and the car would go to almost full cold going down hills. A hill would be like dropping 500 feet or so over a few minutes. The temp will change very fast, like you can actually see the needle dropping. 

PartyPooper2012 > Highlander-Datsuns are Forever 04/08/2020 at 13:18

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hmm... i dont have too many hills here. an uneven road is best I can do.

I was just curious if my car ran hot before or cold now. Seems its running cold now. But not too cold. Temp goes up and stays there. I might consider swapping out thermostat eventually. For now, I just want to burn off some winter fuel. 

PartyPooper2012 > Snuze: Needs another Swede 04/08/2020 at 13:21

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I drive about 15 miles to work. Mostly highway driving. 70s. it has plenty of time to get to temp but it isn’t happening. It did spend entire winter in garage. I wonder if maybe something weird happened while put away with tstat or coolant. 

PartyPooper2012 > XJDano 04/08/2020 at 13:24

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Yeah. It seems that way. Odd tho. I changed it fairly recently. 2 years ago... maybe 15k Miles ago.

But then again... GM dealer had been under the hood and may have changed it out to some shitty one.

No matter. It’s not a hard job or expensive one.

I am just wondering. Hypothetically, what would be a down side with car running cooler? 

Snuze: Needs another Swede > PartyPooper2012 04/08/2020 at 13:31

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Yeah, I think it’s got plenty of time, especially highway cruising. My issue is only in very cold temps.  But yeah, I think maybe over the winter your tstat got stuck or something. 

ttyymmnn > PartyPooper2012 04/08/2020 at 13:45

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This is a C5. Hope that clears things up. 

TheRealBicycleBuck > PartyPooper2012 04/08/2020 at 13:49

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Incorrect temperature can lead to strange running conditions as the computer tries to adjust it back to the optimum temperature. That can result in a high idle or power loss or it running too lean.

atfsgeoff > PartyPooper2012 04/08/2020 at 14:10

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Modern engines designed within the past 30 years are generally most thermodynamically efficient and have lowest emissions when operated at relatively high temps. The LS1 in a C5 is most efficient around 220F. Low fan kicks on at 226, high fan at 235.

PartyPooper2012 > TheRealBicycleBuck 04/08/2020 at 14:15

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interesting. OK. I guess I will be replacing the thermostat.

Know anyone who wants an old thermostat? 

The Snowman > PartyPooper2012 04/08/2020 at 18:33

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Take it out and boil it to test.