Ok, here’s the issue. 2010 HHR SS Canadian import with 24k. Yes, I know…how did I get such a low mileage HHR SS in 2016. It had 16k when I bought it as the previous owner was going through a divorce and traded it in. It was his wife’s and I guess she never drove it much in the bitter winters near Montreal.
Anyway, I’m having disappearing coolant issues. I first noticed this when my over-heating coolant light came on. I checked the coolant level and it was low approximately 1.5 qts. I refilled and have been monitoring the level since. 4 days later the level in the coolant reservoir was down 3/4”. I’ve checked all the hot spots for leaks (radiator ends, tees, water pump, etc.) no visible leaks apparent. Also, no coolant was found in the oil and I haven performed a pressure test on the cooling system yet, but will this weekend. My question is twofold. Did the Canadian HHR SS’s possibly use 2009 engine blocks? And, how can I tell the manufacture date of the block itself? I would assume that since it was sold as a 2010 that it has the block that was not prone to cracking. But I might be wrong. Also, it was sold as a Certified Pre-Owned car so I’m assuming that it might be covered. If not, my 1 yr. 12K warranty expired 4 months ago. I am reading horror stories about block porosity causing cracked blocks on the earlier versions but not the 2010. Also, if there are any GM service technicians that could run my VIN number as I would like to know the date of manufacture.

 

Your date of manufacture is stamped on the inside of the drivers door sill on the b pillar. I've also read quite a few of the horror stories about coolant loss and porous blocks recently after noticing my coolant overflow was empty a week ago while changing my oil. I've never had any issue with overheating and usually run between 190-200F, no sign of coolant in the oil or vice versa. At any rate I ended up adding about half a gallon of premixed dexcool and about half of it disappeared in the next few days. The good news is that it has since leveled off and stopped using coolant so the system must have just been lower than whatever fits in the expansion tank. The bad news is that I have no idea where it went in the first place and my car is an 09' that was made in July 2008 which is smack in the danger zone from what I've read here and on the cobalt forums (mid 2008 through late 2008 seems to be the majority of the problem so it's late 2008 and early 2009 models that are affected). I've never really paid much attention to coolant levels on any of my previous cars as the level never changed, I'll be keeping closer tabs on this one though.

 

ALL HHRs were built in Mexico in the same plant.

Have you thought about head gasket. Compression/leakdown tests.

I am pretty sure the "block porosity" issue was pre 2009. That does not mean "cracking" it means a pin hole.

If the "overheat" light came on you may have more damage than you expect. A change of DexCool at least.

Is it possible that somebody replaced the coolant, and did a bad job? What color is the coolant?

 

Followup: It seems that everything has resolved itself. The only thing I can think of was that there was air within the cooling system from the factory. Ever since it was refilled and all the components checked it has held at the factory recommended level in the coolant reservoir. I will continue to monitor and flush the system at 35k.

 

Thanks for the follow up! Maybe the PO changed the Dexcool at the 5 year mark as the manufacturer recommends and didn't burp the coolant system!

 

DexCool has a life of 5 years. If it was installed at the factory it is overdue for a change.

 

But the OP wouldn't be 100% sure if it was changed or not! Sounds like the PO was fastidious with maintaining the SS

 

From post #4
"The only thing I can think of was that there was air within the cooling system from the factory."

That's what I was talking about.