leija210

I have a 2006 Equinox and coolant is boiling out of the top of the surge tank.. The temp gage never goes higher than the half way mark. There doesn't seem to be any leaks anywhere. I have replaced the thermostat, didn't work.. Replaced the sensor, didn't work.. Just replaced the fans, and STILL DIDN"T WORK! After sitting idle for a little while, out comes the boiling coolant! Anyone know what else it can be??

tech2

the symptoms you describe sound like a cooling system that is not sealed so it can't pressurize. the system must seal as the increased pressure raises the boiling point of the coolant. if it can't pressurize, it boils over at normal operating temperature.


have the system and cap pressure tested. a cap that does not seal will cause this.

Buddy0817

make sure fan is operating properly. it might be blown fuse

leija210

Turns out there WAS air in the system, and so far so good. It hasn't boiled over again, so thanks for the tip! BUT, now that is hasn't been boiling upwards, we noticed it's been going down, and I don't know where the leak is, or if there even is a leak. There is no residue on the engine anywhere, no steam, no smoke, and def no puddles or drips from under the car. I do smell a mild burning smell through the ac vents when driving. We filled it to the proper line after bleeding the air from the system and over night it was more than half way gone. We filled it up to the line again, and after driving it was down another quarter. Any thoughts?

tech2

the system should be vacuum filled to ensure all the air is out. If it is poured in at the reservoir, you may need multiple thermocycles for the system to draw in the coolant and expel air. Sometimes its very difficult to get it out.

keep filling it up and see if it settles out. if not, time to pressure test.

Communer

I experienced a different twist on this phenomenon. After I started my 2002 Malibu to go shopping, the Low Coolant light came on. As this has happened in the past with no problems, I decided to wait until I returned to add more coolant, which was unusual because I added coolant the previous week. I have never detected any leaks. During my travels, the light mostly stayed on, but went off for brief times. At no time did the temperature gauge read above normal. At my last stop before returning home as I was parking, steam came from the engine compartment. Opening the hood, I saw coolant boiling out of the hose from the surge tank, similar to what the OP wrote.

Fortunately, I was near a hardware store where I could buy more coolant. I poured in the usual amount and drove home with no problems. At home I checked the fan fuse and let the engine idle until the temperature gauge was one mark above the hottest I recall ever seeing it. The fans did not turn on and there was no boiling.

I phoned my local Chevrolet service department and the advisor opined that my thermostat was stuck. If this is what happened, it would be the first time since I bought the car in 2002. If my coolant was low according to the light, why would it boil out? I would expect the temperature gauge to go into the red zone, but it did not go near it.

Other questions are: should I replace the thermostat or never again ignore the Low Coolant light and check it soonest?

tech2

if the coolant is low, the temperature sensor is probably reading air temp not coolant temp..so the gauge will not register a overheat condition.

the first thing you need to address is the low coolant concern. If its continually low, pressure test it and look for the leak.