Overheated - what to look for?
 

My daughter was driving the HHR today and it overheated. The needle was pegged at the top and "Cooling Mode On" was on the readout. She stopped it right away, but didn't send me a text until 2 hours afterward :duh:. By the time I got there it had cooled down.

The belt was still on, so I started off by adding water to the overflow tank, which immediately ran out the bottom (will have to look into that tomorrow). I then took off the cap on the upper hose and it was filled. Oh well, start her up and see what happens. I drove the 20 miles home in stop and go traffic and the gauge stayed one notch below middle like it always has.

Any ideas on what would cause a sudden overheat and then back to normal? I'm thinking that the cooling fan possibly stopped or the thermostat was stuck closed. Any other ideas on what to check?

1. Change the DexCool now, it does not react nicely to overheating.

2. The belt does not drive the water pump, the balance shaft chain does.

3. I don't know why water would run out the bottom of the expansion tank, other than something is broken.

4. The T-stat probably should be changed, it's easy to do.

5. the cooling fan only runs if the A/C is on OR the coolant temp gets up to about 219F, then turns off at 180F (the t-stat temp).

6. year, model, mileage would be helpful.

Thanks. I'll figure out whether it's the expansion tank is broken or a hose. I did notice that the coolant was a brownish color, so it definitely needs to be changed anyway. I'll replace the thermostat when I drain and fill the coolant.

It's a 2008 LT model with 134k on it. New to me about a month ago, so still finding some things out about it.

Brownish colored coolant and an engine that ran that hot, not a good sign. You should also check the engine oil for any signs of coolant in the oil.

She could have run it hot enough to blow a head gasket or worse. Best to check it over real good.
Don't want to give her back a car that may leave her stranded.

And get the AC Delco tsat, the others don't open to please the ECM and cause problems then you'll have to do it all over again, and yes Dexcool 50/50 premix is great!

I forgot to mention: replace the pressure cap after overheat event!

Thanks for all the info. It turns out the overflow tank was actually full and it was just overflowing. I've narrowed it down to the fan, which is not coming on at all. I let it get up to around 240 today and it didn't come on at all. And it's only going above normal at a complete stop and especially with the A/C on.

So now at least I have it narrowed down to the fan or the wiring.

Engage the A/C with the engine running, the ECM will command it to start running when the BCM issues a request for fan engagement, if the fan starts its good.

If the fan doesn't start, its suspect along with its connection to the wiring harness.

Also, give the fan a spin by hand, engine off/key out please. If it doesn't spin easily, or if it feels "crunchy", then it's knackered.

All good advice above, but since the engine has gotten to the point of overheating, keep a head gasket or head failure in mind as future occurrences.

Ecotec engines absolutely do not tolerate overheating, they're fairly bullet proof until you cook 'em.