Thermostat and coolant

[Larry227]

Thermostat: The wife has an 01 GA 3.4 w/89000km. It overheated on her the other day. Found a broken o-ring on the rad cap so I got a new cap. Filled the resevoir with dexcool and then ran it up to operating temp to make sure the fans kicked on. (Already established they worked with the A/C). With the A/C off they kicked on about 94*c which should be about 201*f. Temp dropped a degree or two and stabilized. Both rad hoses were hot and pressurized. There was no circulation going through the surge tank though. If the thermostat opened, shouldn't I be getting circulation in there? I want to make sure it's not sticking.

Coolant: I also saw small traces of brownish gunky looking stuff in the surge tank. My first thought was someone used stop leak in the past. After browsing this forum I see where mixing dexcool with other types could cause a varnish build-up. Could that be it? We bought this car used last year so I have no idea what the first owner could have done. I will get it flushed right away.

[GTP Dad]

Have the system flushed and reinstall the Dex-cool antifreeze. I would also replace the thermostat at the same time since it should be removed for flushing anyway. The brown material you see is due to the dexcool's exposure to air. Nothing to worry about just clean it out. The tank is designed to catch overflow when the coolant heats up and expands from the radiator and it will pull coolant back into the radiator as it cools down. You will not see circulation when the car is running. Keep careful watch on the car as overheating can cause a variety of problems especially with head gaskets.

[Larry227]

Thanks