Coolant temperature gauge not working properly (fixed: thermostat)

Hi everyone,

I was driving on the highway like any other workday when I realized my engine was overheating (gauge in the red).
I pulled over and open the hood: full of steam.the big hose to the radiator was bleeding steam.
There was no shop around so I waited for the engine to really cool down, refill with extra coolant I had in the trunk and some water as well.

I drove back home to the closest service center: while driving the temperature gauge was not getting over the first quarter: I stopped anyway to let the engine cool-to be sure. the engine should be pretty warm even if I waited for 2 hours.

The repair shop just replaced the hose.

But the temperature gauge is still not working properly: When I drive on the highway, the gauge goes down to the first quarter.when I am stuck in traffic, or driving in the city, the gauge goes up in the middle (second quarter) like it is suppose to be. going back in the highway makes the gauge goes down again.

Do you guys have any idea of what is going on? looks like the temperature is not read properly, or the engine is not getting cooled properly and staying at a nominal temperature (thermostat problem?). or gauge issue?

Thank you,

Ben

Quote:

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Originally Posted by sheva7

But the temperature gauge is still not working properly: When I drive on the highway, the gauge goes down to the first quarter.when I am stuck in traffic, or driving in the city, the gauge goes up in the middle (second quarter) like it is suppose to be. going back in the highway makes the gauge goes down again.

Do you guys have any idea of what is going on? looks like the temperature is not read properly, or the engine is not getting cooled properly and staying at a nominal temperature (thermostat problem?). or gauge issue?

Thank you,

Ben

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You need to bleed the air out of the cooling system. There is nothing wrong with the temp gauge. It needs to be immersed in a solid column of fluid to give an accurate reading.

First of all, why did you have coolant in the car - had anything else been done to the cooling system recently, or had you been losing coolant? Next, always give the year and mileage - there have been reports of t-stat problems in the later models, and the older ones have the POS plastic t-stat housing which have caused lots of problems for many owners.
Although this MIGHT be air in the system, my guess would be something else because Aveos bleed easily (as compared to some other vehicles), and any half way competent shop should be able to get that done correctly. My guess would be a bad t-stat, unless there had been something else going on that you didn't mention in your OP. You didn't say anything about the current coolant level - is it where it should be, with no visible drips?
But that problem (whatever it turns out to be) might be the good news, because there could be much worst news on the horizon. Having given your engine a steam bath, it's become unfortunately likely that amount of heat has resulted in the head gasket starting to go. I hope this is not the case, but you will need to monitor the coolant and engine performance closely going forward (after you fix whatever is wrong right now).

How do I bleed air out of the system? just turning the fan and heat on?
Since I was not sure if the gauge was working properly I turn the heat on to dump the heat out of the car for a good 20 miles so if it is that, I assume I already did that.

I had coolant in my car because two year ago I had an overheat and no more coolant in the tank. I had it pressure tested and flush and fill and since two years I had no issue. the car was about 55,000 miles at that time.

Today my car has 105,000 miles (my commute is 45miles one way). It is an Aveo 2008.

I drove this morning and checked the coolant level: the coolant is where it should be, no drips. the shop who replaced the hose did a pressure test to ensure no leak. I did not drive enough to see if the gauge would work properly in city and highway.

Ben

To bleed, remove the overflow cap, turn the heater on full, and idle it for maybe 10-15 minutes in your driveway. If it's air in the system, it shouldn't be long before the overflow tank level drops. If that happens top it off, run it another 10-15 minutes,and you should be good to go. I've never needed to raise the front end on my Aveos, but that's a good thing to do regardless - or you can idle it facing up an inclined driveway, etc. Naturally you need to watch the heat gauge while all of this is happening to make sure it's not starting to overheat again due to a stuck t-stat or some other problem. Also very important to check for white smoke coming out the tail pipe, which would unfortunately probably mean a head gasket problem.

update guys:

I idle the engine with the cap off. it did not work.
I went to do a flush and fill because I had to pour water when the engine overheated.
The engine still cool down when I drive on the highway.
Should I replace the thermostat?

Quote:

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Originally Posted by sheva7

update guys:

I idle the engine with the cap off. it did not work.
I went to do a flush and fill because I had to pour water when the engine overheated.
The engine still cool down when I drive on the highway.
Should I replace the thermostat?

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If it has 105K miles on it and the thermostat hasn't been changed...

Change it.

I just changed it this morning. will drive on the highway and see, I'll let you guys know.

The car is now working fine, I have good hot air coming in the engine, and the gauge is showing the right temp!
So Happy! was so easy to do!