I've been having a very weird problem with the cooling system for quite some time, but I haven't figured it out so please help. I should note I've had the coolant system flushed and replaced the water pump about 2 years ago or so.

1997 Sunfire 2.2L Auto
129,00 miles

My low coolant light seems to stay on quite a bit, but everytime I check the coolant reservoir, it looks full. Sometimes the light will turn off for a day or two, then come back on for a week or so straight.

It started overheating today on the freeway (75mph) as the temp gauge needle reached the "high" mark before the orange/red. The weird part is that if the "low coolant" light was on, the temp read about 3/4 up at highway speeds or right below the high mark. The "low coolant" light would turn off occassionally while driving at highway speeds and if I slowed down, the temp would climb quickly. Occassionally I'd come to idle in traffic for only a few seconds with the "low coolant" light still off and the temp would skyrocket. Once I got going it'd drop down, yet still read somewhat high. If the coolant light was on, it doesn't really seem to overheat while idling.

When I got home, I gave the car a chance to cool down for a few hours then checked the coolant reservoir and it was empty. It took about 3/4 of a gallon before the reservoir was full. I also noticed what looked like coolant below the reservoir. It was wet under the reservoir, but no puddles under the car or anything. There was also white residue on that side of the bay and on the underside of the hood on the passanger side. Not a lot, but noticeable. Could the reservoir be dumping coolant while driving and making a mess under there, perhaps hitting the belts and shooting it onto the hood?

I've also noticed the car exhibits weird overheating issues far more often when it's cold/cooler outside as opposed to a hot day. I hardly ever see the temp outside the center on the temp guage when it's hot outside. Heater and AC seem to work fine, as I haven't noticed anything weird there.

Anybody have any ideas what the problem could be?

The car drives fine. No power issues, stuttering, or anything like that.

I have seen it before,not very often where the plastic tanks develop a small crack in the bottom of them.

Do you have a handheld temp gauge, you need to figure out if the vehicle is actually over heating ( which it might be due to coolant loss) or if you gauge isnt working correctly.

Next time it reads towards the high side, you need to point the temp gauge at the thermostat housing and do it at the hose right where it comes out of the housing, just to compare the two of them, and see what the actual temp is.

Your low coolant light on when its full, it due to that sensor in the bottom of that tanp, which if that seal seeps, which may be your issue as well.

Heres how that sensor works, has a float if you will in tank, as the tank is empty that float, well doesnt float, and contacts what the float is connected to, and it completes the circuit, basically giving it a ground, and it turns that dash light on.




- 2004 Cavalier - 124k, owned since new

Sorry to hear about your troubles.

I hope with the low coolant that you haven't created head or head gasket problems! Keep and eye on it.

I'm going to preach at you first.
Warning lights were installed on cars to WARN you of a potentially serious problem and that you need to STOP driving now, pull over, pop the hood and visually check out what is wrong. Fix it if you can, if not get it towed to get it fixed. To continue to drive is really not a good idea. There are exceptions to this IF you are very knowledgeable about cars and their repair, they can sometimes be nursed home under their own power with no additional damage.
If you ignore the lights and continue on your merry way serious problems can and will arise. Warning lights are NOT suggestions to check it out sometime in the future, the only exception is the Check Engine Light (CEL). All the others indicate STOP NOW!!!!!

The tank looking full could just be a stain at the full mark from the coolant being in there over the years. You really need to verify that it IS full, not just LOOKS full.

That being said, you are losing coolant obviously. As already suggested the plastic tank could be the issue, it could be the hoses feeding the tank, it could be the water pump, it could be a stuck thermostat causing it to run hot thus increasing coolant pressure and causing the pressure controlled top to vent out coolant.
It could be the metal pipes that run the coolant to the heater are rusty and leaking, It could be the rubber hoses on the heater circuit or to the radiator. There is a small hose form the water pump to the heater pipe. Etc.

Sadly, it could also be a bad head or head gasket. These engine are famous for them going bad.

Whatever the problem, do one thing today.......stop driving the car until this is fixed.

Dave

I hate to tell you this, but i had the exact same issue. i had a very small head gasket leak that wasnt noticeable until yesterday when i did a coolant flush, and the head gasket let go completely. I had the same problem with the low coolant light and everything. Doing a new head gasket today...lol I also just did a new water pump, heater core and thermostat approx. a year ago. I hope your issue isnt the same as mine turned out to be, but you are having the EXACT same issues that I had. Good Luck!