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Faulty Thermostat..already?

Canned Heat

By Canned Heat
in Ask A GM Technician

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Canned Heat Enthusiast

Canned Heat

Posted
Posted

My '07 Sierra Cew Cab with 4.8 came with factory remote start, which is a bonus...but I get going this morning after a 10 minute warm-up and get 2 miles down the road and my temp gauge is reading about 225+/-. It goes up a hair more and comes back down to the 210 norm. It spikes about 3 more times never going above the 230 mark.

 

The truck has 974 miles on it....WTF?

 

Taking it in today...

minibike132 Senior Enthusiast

minibike132

Posted
Posted

The unpressurized boiling point of coolant is 212 degrees the cap lets pressure build and for every pound of pressure boiling point goes up 3 degrees. I don't know what the cap is rated at but lets say average is 15lbs that would bring the boiling point to 257 degrees. The t-stat opens around 210 and the fan shouldn't even be working till about 220 so I wouldn't really worry about 225. If you are take it to the dealer and with a scan tool they can tell the exact temp the gage may even be a hair off.

Canned Heat Enthusiast

Canned Heat

Posted
  • Author
Posted
The unpressurized boiling point of coolant is 212 degrees the cap lets pressure build and for every pound of pressure boiling point goes up 3 degrees. I don't know what the cap is rated at but lets say average is 15lbs that would bring the boiling point to 257 degrees. The t-stat opens around 210 and the fan shouldn't even be working till about 220 so I wouldn't really worry about 225. If you are take it to the dealer and with a scan tool they can tell the exact temp the gage may even be a hair off.

 

Thanks.

Heavy workload in the office...won't get there til later today. The MAX of the temp gauge is 260. I would've shut her down before it got that far. The 225 was a guess, but it got just short of the 3/4 line. At the top, it's 210 and at max it's 260 so it would've been pushing the 230 to 235 range, Either way, that shouldn't be happening to a new truck with short of a thousand miles on it. It is an '07 and probably sat for awhile. I'm sure it's feasible that a thermostat could go on it...just surprising.

 

Spoke with the service big wig at the dealer....he says this could be common based on the fan or the motor wanting to run that hot. He says it's typical of alot of GM front wheel drive cars. I hate the thought of having to watch the gauge that carefully anytime it's cold out.

Zembonez Senior Enthusiast

Zembonez

Posted
Posted

The factory gage isn't a very scientific instrument. It really just gives you a general idea what the engine is up to rather than a precise temperature reading... hence the very wide range on the cool to hot scale. My 07 runs about 1/8" beyond the 210 mark when it is hot and my 05 never got up to the 210 mark.

 

I would certainly keep an eye on it (as you obviously are). Probably not anything to worry over... especially if it never gets any higher. Might bring it up at your next service visit. It is possible that you have a sticky thermostat.

Canned Heat Enthusiast

Canned Heat

Posted
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So they replace the thermostat a little while back, and everything's been fine. I get gas this morning and start the truck back up....it's cold out and run in for a coffee. I come out and I can here the fan just roaring and think to myself: "I bet the temp gauge is up" and sure enough, it's around the 225 mark again. I drive away watching the gauge and within a minute it dips back to the 212 mark and stayed there for the remaining 26 miles. How long til this goes haywire again??? I'm tellin' ya......

LAGA Enthusiast

LAGA

Posted
Posted

Something is not right here. You should not be getting these spikes in engine temp in winter. My 07 NBS VMAX has never gone over the 210 mark even in summer, and I have not heard the fans come on in months. Could be a bad water pump or a clog in the radiator or even a air bubble in the system. Just my .02

Canned Heat Enthusiast

Canned Heat

Posted
  • Author
Posted
Something is not right here. You should not be getting these spikes in engine temp in winter. My 07 NBS VMAX has never gone over the 210 mark even in summer, and I have not heard the fans come on in months. Could be a bad water pump or a clog in the radiator or even a air bubble in the system. Just my .02

 

So I take it in on Friday and it does nothing with no signs of a temp spike. I start it with the factory remote this morning, it runs for the 10 minutes and shuts off. Start it again and come out after 2 or 3 minutes and it's blowing cold air, windshield's still frosted, etc. Flip the key over to fire up the gauges, etc., and the temp gauge is reading the 225 to 230 again after no more than a minute. Get out of the subdivision and it drops back to normal and the heat kicks in. Stop on the way to work (5 minutes later)...let it idle for 2 or 3 minutes and I come out and temps back up and now the fan is roaring. Keep in mind it's 19 degrees out. Talk to my sales rep this morning and he tells me a guy we both know is having the same issue with his. Same 2007 Sierra Crew Cab. Don't know if he's got the 4.8 though.

 

If anyone else is having this issue, gimme a shout. Dropping it off for a loaner tomorrow.

Canned Heat Enthusiast

Canned Heat

Posted
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Good detective work LAGA.

 

Left it there last night and got a call a little while ago that there was an air pocket. Due to a faulty spring clamp that must've leaked anti-freeze some time ago. They checked for leaks when I had it in and I've never had a leak of anything since I've owned it.

 

Told the service manager of the possible culprit (from suggestions here and otherwise) and got the smartass smirk from the guy when I mentioned, water pump, blockage, and AIR/VAPOR POCKET. Turns out it was just that..they found it by pressurizing the system. You would've thought that when they replaced the thermostat, like last week, they'd have noticed that. Trial and error I guess.

 

That's why this forum kicks ass.

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