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99 Saturn SL2 overheats only in summer

The car overheats in 90 plus temps when stuck in traffic or idling in drive through. Have taken it to two different mechanics who can find nothing wrong. The fan works the coolant circulates and the thermostat appears to be working although the last mechanic offered to replace it for me though he didn’t think that would work. I think they think I’m crazy. Any ideas. Would like to keep the car running for my son.

How much does it overheat, is it a gauge or idiot light? What is the mileage? could it be normal? Might need a radiator cap, or radiator-engine flush, new antifreeze, or new radiator. If the thermostat operates normally otherwise, I would agree with the mechanic it probably would not help. A cylinder pressure test might be informative, in case of a head gasket leak that could cause overheating, maybe too many bugs on the radiator, a good mechanic should be able to help pinpoint any weakness in the system.

Those symptoms typically mean the fan isn’t coming on, but you said the fan is working. Another cause is a radiator cap that isn’t sealing, but that is usually accompanied by an elevated temp while pulling a hill or long grade.

One more thing, if you’ve never changed the coolant, or have changed it to the old fashion green stuff, not the new “mixes with all types” or dexcol, then you could have some “gelling” of the coolant. Normally I do not recommend flushing of the cooling system, but if this is the case, or at least a possibility, then I would recommend a power flush, but not a chemical flush. For that you need to see a professional mechanic with the proper equipment.

You may want a pressure flow test of the radiator. Radiators wear out especially(not sure if case) if coolant is not changed out at specified intervals.

is it over heating for sure or is the guage just going up to the red?
on saturns the fan does not kick on unitl it hits the 3/4 mark (right at the red) this is normal. normal op temp while driving is between 1/4 and 1/2. Idle and stuck in trafic will cause temp to rise to almost the red mark then teh fan will kick on.