Overheating Options

[Moobit]

Not really sure what this can be. No signs of a leak.

I have 2 videos. Quality is just plain bad but it shows what i need to show.

One shows when it warms up. It is under C and then in a couple of seconds it goes up to norm operating temp.

http://www.youtube.com/watch?v=nq9B5FR-VGg

Second one shows when its at norm operating temp and then goes up slowly. Only seems to heat up at idle. As soon as the temperature goes up i accelerate and then the temperature suddenly goes back to normal.

http://www.youtube.com/watch?v=paE0S3BwTlg

Not sure if this might be a sensor problem. I have never really encountered this kind of problem where the temperature would change so fast.

Any ideas what it can be?

[Galcobar]

If I'm reading that second video correctly, the car's not actually moving -- you're revving the engine while parked.

That does suggest it's something to do with coolant circulation. However, it still might be an issue with the temperature gauge sender, which is seperate from the temperature sensor used by the ECU, or the temperature switch on the radiator which controls the cooling fan. Happily that sender is a very cheap and easy replacement, and also easy to test with a multimeter to see if it's still offering the proper resistance.

Usual first step is to check that the coolant level is adequate; with the system cold there should still be coolant in the reservoir (between the LOW and FULL lines marked on the reservoir). Otherwise, the system is sucking air into itself as the coolant temperature drops and the coolant volume falls. If the system is low, fill it up and watch the reservoir's behaviour with the car at operating temperature.

If your radiator cap is not holding adequate pressure, the coolant will boil and you'll lose coolant from the reservoir, which leads to the system getting air into itself when it cools down. That air, plus the bubbles created by boiling coolant, can block coolant flow and in turn lead to more overheating. This might also explain why your temperatures fall when the engine is racing, as the higher engine speed turns the water pump faster, creating more enough flow to force the bubbles to move.

Does the temperature gauge drop when the car is actually moving, but the engine speed is low and constant -- in other words, while cruising? If it does, that tells you the thermostat is probably stuck open. The thermostat should start opening at 80-84C (rated for 82C) and open a full 8 mm at 95C. You can also check the thermostat by comparing the temperature of the upper hose (coolant runs from the engine to the radiator) against the lower hose (coolant runs from the radiator to the engine). If the engine is hot but the lower hose is cold, that tells you the thermostat is closed.

Does the radiator fan kick on when the car is idling and the temperature gauge spikes? If not, check that the fan works by unplugging the temperature fan switch, which forces the fan to run. If the fan runs, check the resistances on the temperature fan switch to see that they're within specifications. The switch is supposed to turn the fan on when the coolant temperature in the radiator reaches 93C, which it does by losing continuity at that temperature.