Overheating issue

[daltron]

2008 Aveo5 98K~ miles

Over the last couple months I have been having to replace the coolant in my Aveo. I can see no leaks and no signs of a blown head gasket. It just occured to me as of writing this, maybe the overflow cap (since my 2008 does not have a radiator cap) is the culprit. I will replace that this weekend and see if it helps the coolant consumption issue.

However, on to the real problem. My wife drives the car and told me it was beginning to overheat again, so before we went out last night I filled it will coolant. Hard to gauge how much it took, but not much at all. Maybe 20-40 oz. We drove it about 13 miles to the restaurant, and I noticed the car as overheating. Here are the things I know:

1) the upper hose is very hot, but the lower hose does not feel hot at all
2) if I turn the heater on, the temperature gauge goes back into the 45-50% range and the car does not overheat
3) I replaced the cracked plastic OEM thermostat housing and thermostat last year (not that it couldn't have failed so soon, but just saying)

Thoughts? I guess the simplest fix would be to change the thermostat again, since the lower hose is not getting hot. However, if the thermostat wasn't opening would the heater being on help at all?

[USAFzac]

If one hose is hot and the other oin isn't that sure sounds like a therrmostat. Crawl underneath, check out your water pump, on other vehicles I have seen them jam up. Masks sure there is no coolant in your oil,and vice versa. You wanna make sure it isn't your head gasket

[thankful_ragamuffin]

A bad pressure cap can certainly impede circulation. That may be the first place to start. The 13 mile drive to the restaurant, was that stop and go or freeway? Is the engine cooling fan invoking? Is the gauge pegging at hot or just running much higher than normal? Does coolant appear to be circulating? Have you flushed the coolant system at any time? Can you feel the face of the rad for hot or cool spots?

[daltron]

If one hose is hot and the other oin isn't that sure sounds like a therrmostat. Crawl underneath, check out your water pump, on other vehicles I have seen them jam up. Masks sure there is no coolant in your oil,and vice versa. You wanna make sure it isn't your head gasket

No oil in the coolant or coolant in the oil. Not sure about the water pump.

A bad pressure cap can certainly impede circulation. That may be the first place to start. The 13 mile drive to the restaurant, was that stop and go or freeway? Is the engine cooling fan invoking? Is the gauge pegging at hot or just running much higher than normal? Does coolant appear to be circulating? Have you flushed the coolant system at any time? Can you feel the face of the rad for hot or cool spots?

It was a combination of streets, a little traffic on the freeway, and a few miles of no traffic on the freeway.

With the heater off, the temperature guage would slowly climb past 75%. When I turned the heater on, it would eventually drop back down to mid-level.

I am not sure about the fan, I will have to check that today. I am not sure if it was ciruculating, but the heater blasted very hot air when on but the bottom hose was not hot.

I am not sure about the definition of flushing, but I did replace all the coolant last year when I replaced the thermostat. Earlier in 2013 I also replaced the upper radiator hose and the radiator (it had a crack in it).

I have an infrared thermometer, so I'll try to see if the rad has any cool spots.

[thankful_ragamuffin]

So, no stop and go traffic, good airflow over the rad. Rad is new, so not likely plugged. It is running hot, but not to Chernobyl levels. Minor loss of coolant over time, but no noticeable oil in coolant or coolant in the oil. Final test for coolant in oil - remove the oil fill cap and test taste the condensate on the inside of the cap. If it is sweet, there is coolant in the oil. I am leaning toward a bad cap. Some parts stores can pressure test it for you before you buy a replacement that may not be needed.

[daltron]

So, no stop and go traffic, good airflow over the rad. Rad is new, so not likely plugged. It is running hot, but not to Chernobyl levels. Minor loss of coolant over time, but no noticeable oil in coolant or coolant in the oil. Final test for coolant in oil - remove the oil fill cap and test taste the condensate on the inside of the cap. If it is sweet, there is coolant in the oil. I am leaning toward a bad cap. Some parts stores can pressure test it for you before you buy a replacement that may not be needed.

Sorry I wasn't clear before, but it will get past the 3/4 marker, I just turned the heat on so it wouldn't hit the red mark. I'll check out the oil cap and replace the overflow cap, though.

[daltron]

Replaced the overflow pressurized cap, still same issue. I rented Autozone's cooling system pressure tool, but it is meant to work with traditional radiator caps/openings and will not work so I can't test that.

The next thing I can think of that is cheap is just to replace the thermostat again, although if the upper radiator hose is blazing hot, the radiator's temperature decreases from top to bottom, and the lower hose is cooler than the top, I can only assume the thermostat is indeed opening letting the coolant in.

I also left the cap off and let the car idle. No bubbles, nothing. Turning the heater off and putting it on cooling it immediately rose and splashed out all over the resavoir. Turning the car off also did this. After refilling the coolant and trying again, I could not replicate that. I guess it had air inside the system, but either way that does not seem to be the issue.

Also, unlike yesterday when the heater on would make the temperature gauge return to midway, now it's anywhere from midway to 60% ish. Just an observation.

EDIT: I also noticed that compared to yesterday when I filled the system and when I took off the cap today, the level of coolant inside the reservoir had RISEN a couple inches.

[USAFzac]

That sounds like its stuck shut... Is your fan engaging?

[daltron]

My fan is engaging.

When you say stuck thermostat, wouldn't the upper radiator hose be cool then? If the thermostat is open, then it should be hottest to coldest from upper hose > radiator > lower hose, no?

[avguy]

You have a lot going on there, and it's almost as if there are 2 separate problems. The part about overheating after the coolant has been topped off makes no sense at all. You have a coolant leak and overheating, but they don't seem to be connected. Even a broken water pump impeller wouldn't explain the coolant leak. And a bad head gasket wouldn't cause the overheat until the coolant level goes down.

Although it's far-fetched, a blocked and also leaking radiator is only thing I can think of that could be a single cause of everything that's happening to your Aveo. Something like a broken weld causing a partial closure of the rad passages inside, and also a tiny leak to the outside. Of course, even the smallest pinhole rad leak should give off that distinctive coolant smell, which (I assume) you aren't getting. But just for the heck of it, you might want to check online for complaints about the rad model that you used for the replacement. Sounds like the overheating is getting worse, so real soon you're probably going to have to begin disassembling the cooling system to find the problem(s)