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.

That my friend is the right attitude to have.:thumb:

HHR's are machines, no matter what anthropomorphic personalities we might assign to them.

And machines will break, malfunction, or fail. When that happens, diagnose the problem, fix it, and keep "Keepin' On".

I hope you get it fixed before it fixes you, George. It's not your DD, though is it?

Nope, not my DD. Just my fair weather car. It doesn't see rain or wet roads.

Understand that.. mine serves the same duties, although it's been caught out in the rain once or twice. Heck I still have the factory wiper blades and washer fluid.

Just a little update for those that are interested. 1st. I haven't changed the t-stat or dexcool yet.
Something I've noticed is this seems to be only on a cold start to warm up issue. I've driven it 3 times since my original post. Each time it's been from a cold start, the temp has climbed to 217, 219, and 225 before the T-stat seems to open. The temp will then quickly drop back to the 183-185 range in about 15 seconds. It will stay in the 183-187 range for the rest of the time.
The couple of times it was restarted when warm, the temp stayed at the normal 183-187.
I'm still thinking that the T-stat is just slightly sticking when warming up, thus the reason for the initial higher temps.
Once the temp drops back down, it takes such a short time to cool down, I guess the T-stat is fully opening.
Checked the fan operation and that appears normal. It does come on at initial startup( I think only the SS does this )

Anyhow. Still going to pick up a new T-stat and dexcool and get that changed out soon.

Don't forget how Dexcool gets all wierd when heated above 210 or so! That could cause issues with the thermostat, plus age it's going on 6 years old.

Dexcool is NOT hurt by temperatures of "210 or so". Proper mixtures provide protection to the 260 mark for example. And many GM vehicles, including mine, have experienced temperatures of 220 -230 at least a couple of times in the summer..... especially when exiting the valley and heading to the mountains and utilizing Sunset Point climb. But 210 is experienced at least once a day by every vehicle.

I'm sure OB meant 240F. He does C normally.

I have experience with DexCool and overheating. It gets clumpy and lots of particulate.

It was your issues that brought the overheated problems of Dexcool to mind, Don. And I did mean 240 degrees F, I don't usally do C in this forum