2006 Chevy Aveo Overheating

My friends 2006 Aveo started overheating about 2 months ago. Started out just a little so I wasn't worried about it. However it started getting worse. Now it climbs to about 3/4 on the gauge and the A/C gets warm. If the A/C is left on it continues to climb. If you turn the heater on though, it rests about 3/4. A year ago I replaced the thermostat because the OEM plastic housing was cracked, so I didn't think that was it. I have since replaced the water pump. I pulled the radiator and cleaned it out, it is perfectly clean inside. Coolant is clean, and full. Also performed a hydrocarbons block test to check for a bad head gasket, twice actually, and it passed both times. It's got me beat, I have no clue what it could be. Any ideas?

I suspect the cooling fan is either not kicking in, or only running at low speed (2 speed cooling fan if memory serves). The warm A/C tells me there is probably insufficient airflow over the condenser (and rad) either due to the fan or air blockage. You cleaned the fins on the rad and condenser when you cleaned the rad out, right?

Yes I washed it off with a pressure washer. Radiator actually looked really good. I also checked the condenser for any blockage, cause that was my first thought that something got trapped. The fan works, it kicks in at the right time, and comes on with the A/C as it should. Also it doesn't heat up as much at an idle, but gets really hot going down the road.

Do you have access to a scan tool that will read actual temp versus what the gauge is showing or even a laser thermometer? It seems you have done your due diligence in checking all the normal possibilities. Overheat at highway speeds with the high airflow over the rad is rare. You didn't mention if you checked or replaced the rad cap.

Yes I have an Infrared Thermometer. It reads about 230 at the back of the thermostat housing, so its definitely hot. And no I have not replaced the cap on the jug, as it is just a screw on cap. Started without the cap on earlier, and it started boiling out at just above half, which I found odd. But the cap was off so the system wasn't under pressure.

Sounds like it's either a broken water pump impeller, or more likely the thermostat. Yep, I see you replace it last year, but $hit happens.

Yea I'm gonna pull the stat later and run it without it and see what it does, gonna flush it too, maybe something got stuck in a water jacket or something. But I replaced the water pump hoping it was the impeller but that wasn't it.

i once put a thermostat in a maintenance, and the car overheated the first time i started it. put in another thermostat, problem went away..


not saying that is your issue, your description suggests the fans, but since you say they are working properly i would do the thermostat again I guess. But a bad thermostat would keep the rad cool, meaning your AC would not get hot.

now when you say you did a hydrocarbon block test, what did you test? a sniffer looking for escaped exhaust around the head? or the dye test of the coolant? If the head gasket is compromised, it does not always leak out of the side go the block. But If the coolant heated up and boiled with the cap off, how long did it take? I have let 4 cylinders idle a long time without them boiling over (10-20minutes) so if it boiled over quickly, you might want to do a cylinder leak down test to see if the head gasket is blown to the oil or, more likely in this case, water jacket.

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Originally Posted by petrified.rabbit

i once put a thermostat in a maintenance, and the car overheated the first time i started it. put in another thermostat, problem went away..


not saying that is your issue, your description suggests the fans, but since you say they are working properly i would do the thermostat again I guess. But a bad thermostat would keep the rad cool, meaning your AC would not get hot.

now when you say you did a hydrocarbon block test, what did you test? a sniffer looking for escaped exhaust around the head? or the dye test of the coolant? If the head gasket is compromised, it does not always leak out of the side go the block. But If the coolant heated up and boiled with the cap off, how long did it take? I have let 4 cylinders idle a long time without them boiling over (10-20minutes) so if it boiled over quickly, you might want to do a cylinder leak down test to see if the head gasket is blown to the oil or, more likely in this case, water jacket.

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If this is the case you should be able to check the oil. If there is grey matter in there, a classic sign of oil & water mixing, then what rabbit says is conformed.

Well pulled the stat over the weekend and put it in a can of water and heated with a torch. Got it way above boiling and it never opened. Stuck a new one in it and runs at perfect temp. $5 and 15 minutes after spending hours. Oh well, never rule out a new part folks! Thanks for your help!

It became a lot easier to diagnose this one because you said the coolant was clean and full, which eliminates a lot of possibilities. So kudos to you for supplying the necessary detail - most others don't. Glad it was a quick and inexpensive fix :thumbup:

I'm having the exact same problem. Running 3/4 hot while driving, AND my air-con blows warm after a few about 5 minutes. Did a coolant flush to no avail. I was ruling out the thermostat because it stuck closed and blew off last summer, so it's pretty new. I'll change it and report back.

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Originally Posted by Scanman

If this is the case you should be able to check the oil. If there is grey matter in there, a classic sign of oil & water mixing, then what rabbit says is conformed.

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not to get off subject, but we test this at our school.. only dino oil and old "aluminum" green coolant make gray matter or "milkshakes" as we like to call the frothing when drained. And that only happens if the heat of the blown gasket cooks them together. In fact as a class instruction, we mixed the newer "universal" coolant (green too) with both synthetic, synthetic blend oils, as well as new dino oil. Once stirred, you could not tell which was which aside from a slight browning in the dino oil from color. They all mixed scarily well, and throughout the course of the day did not separate. Which is long enough in an engine to spin a bearing. We cooked them the next day to see if they would foam or separate and the still maintained mostly undiagnosable characteristics of being mixed.

Also not all oil/water failures allowing them to mix are not limited to the head gasket alone anymore. So it is even more important to check losses and additions in capacity of each system.

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Originally Posted by Flannelman

I'm having the exact same problem. Running 3/4 hot while driving, AND my air-con blows warm after a few about 5 minutes. Did a coolant flush to no avail. I was ruling out the thermostat because it stuck closed and blew off last summer, so it's pretty new. I'll change it and report back.

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it helps to verify the other parts of the system are working like the OP did too.

I checked then fan of course, which is working, but I don't know of an easy way to inspect the water pump. It was replaced a few years ago.

The T-stat became the prime suspect for the OP because the coolant level in his Aveo remained the same, and also clean. If that's the case with yours as well, then definitely try a new stat. Inexpensive and easy to do for a DIYer. Only if that didn't work would you consider pulling the WP and radiator.

Right on. Our problems were very similar, it was uncanny.

My t-stat lasted almost exactly 1 year, exited warranty and failed. Nice work "Dura-Last"

Switched it out and all is right in the world.

One going bad is a fluke. Is the second one the start of a trend? Time will tell on that.

It's typical on these forums to never see a follow-up of a problem posted - happens that way most of the time.
So when a thread gets a result from the OP, plus another person posts an outcome as well, that has to deserve a
:occasion5:

My stock t-stat lasted close to 120k miles. The replacement lasted 1 year and maybe 4k. hmm

The stat I replaced a year ago was the original, only reason I replaced it was because the plastic housing was cracked (plastic housings are junk IMO) and the new housing came with the stat. It was a house brand at O'Reilly, piece of junk. I recommend Stant if you're going to replace a Thermostat or Radiator Cap.