Coolant temp shot up
 

The temp on my SS normally stays in the 187- 199 range dependent on rolling down the road or stopping at lights.
So today I'm at a red light and my RPD reads 216. Never seen it past 205 before so I was concerned. I left the red light and went about a 1/2 mile to the interstate on ramp. Now it's up to 225. ???
Onto the interstate it holds that 225 temp for about a mile. Then suddenly the temp drops back down to 187 in about 20 seconds.

I'm guessing the thermostat just hung closed then freed up. I'm due to change the coolant anyway so I'll just throw in a new thermostat while I'm at it.
Anyone got any thoughts on this ?

Fwiw. The RPD temp display is always on so I watch it regularly. The RPD and DIC both showed 225 degrees but the analog needle gauge was exactly on the middle notch of the gauge.
The analog gauge seems to be a poor design and I wouldn't trust it at all. If 225 is only the middle of the gauge, what temp does it take to "peg it " into the red.

My guess is that the sensor or gauge is desensitized in the middle.

Sounds familiar.

Lately my wife and I have been going to the local lake around noon to have our nutritious bag lunch and to relax and discuss the daily issues.
Because it has been 10 to 20 degrees for a while now I just leave the motor run and the heater on.
I am always watching the temp gauge on all the vehicles I have owned so nothing new there but the gauge has been steady at about the 4th notch all the time we are there, about 45 minutes or so.
Just for the heck of it I engaged the DIC the other day and found the temp @ 220.
I looked back down at the analog gauge and it had not changed one bit.
My diagnosis was the fans are not starting up. Since then I have been checking where it is while driving on the DIC, it has been running 185 - 195.
This is a 2010 1LT with a 2.4L auto with only 21,000 miles. I just had GM service the cooling system 3 months ago.
After thinking about it I thought do I need a thermostat/sensor change and have a dealer check the Fan function.
Yesterday I thought I would try something. I put the cabin air on inside which I think starts the air conditioner. I let it run for a while and the turned on the DIC to check it.
It was at 183 and stayed there steady for 30 minutes. That setting must have allowed the fans to start and hold that temp.

Bottom line .. is that the fix or should I go ahead and replace the thermostat/sensor and have the fan function analyzed??

Also, the Gauge is a joke.. It goes to the fourth notch and stays there even when the temp is 220.

I have also double checked the cooling fluid level which is rather funky process and it looks to be OK.

Silverfox

My guess is the fan is not turning on.

Unfortunately I know from experience that the gauge pegs at 260*. Hopefully we'll never see that again! I have noticed fluctuations from grandma's HHR. I was waiting in line at the local e check (emissions/smog test) it's required to leave your car running. I only had about 200 miles at the time on the rebuild. Around town cruising it stays between 185-195. While I was parked it steadily climbed to 216-220. Shortly thereafter the fans kicked on, brought me down into the teens where it stayed until I got back on the road where temps returned to normal.

If your temp stayed up after a half mile I would suspect as you have, sticky thermostat.

-my 2 cents

I think you have the right idea George, a new T-stat and Dexcool is in order.

I believe the factory gauge is very forgiving once you've reached the operating range as DrLoch has suggested.

I have an Aeroforce gauge and can watch the temp the PCM is seeing (probably the same as you'd see with the RPD).

My needle gets to the 4th notch up and doesn't move again whether I'm at 185° or 205°.

Seems like the if needle is not in that position, there's an issue. If it's at the 4th notch, everything is with-in an acceptable range as far as the PCM is concerned.

Now that I think about it, I think all of my GM cars have been similar in that design. I know for a fact my Olds Aurora with the V8 was.

Kersh, this is true with most all GM cars I have logged. I believe they have done that so the gauge isn't moving around erratically. I also have an Aeroforce gage that I use to monitor mostly inlet temp after the intercooler.

One of our chief problem solvers with a problem, say it ain't so George!

But judging by the reply's above, I think you'll get it fixed right up, and the analog gauge is only "approximate" at best. But if the DIC ever fails, it's there as a backup.

Yep. That's me. Pretty much 6 years and 46k trouble free miles but this is just a minor hiccup. Nothing to loose any sleep over.
Face it. Mechanical things break, wear out or need maintenance. Some things sooner than others. Some cars sooner than others.
I'm not one of those who complains when something didn't last for a gazillion miles. Nothing is gonna last forever.

I'll just get the correct AC Delco thermostat that has been proven on this site to be the best part for the Ecotec line of engines.
Change out the Dexcool and I'll be good to go.