Originally posted by khoerling
The fans were running after the motor temp rose, but I can't be sure they were running before that, when the temp first started rising.
It takes them a min to cut on... I think the temperature needs to be above the 3rd line for the fans to come on. But keep in mind if there is an air pocket in the cooling system, nothing is really overheating and the fans don't really need to be on.
All the air bubble does is trick the thermostat into thinking the engine is really hot. Thats why the temperature guage spikes. The engine tempearture does not go from normal to HOT to normal again in a few seconds... if it did, the block would crack or something would break under all the expansion and contraction of the alluminum.
As for your car overheating at idle... if I'm not mistaken, there are 2 reasons the fans turn on, 1 is if the car sits at idle for long enough, and 2 once your turn off the car they run for a short period after... If your fans turn on while the car is at idle, thats not where your problem. It is possible you have a very small amount of air in the cooling system, and that air naturaly rises to the upper parts of the cooling system at idle and may be causing the temp guage to rise (I have experienced my car doing this).
How much does the temp rise? and does it rise slowly? and if it does rise slowly, does it also drop slowly?