My '98 4.0L Explorer Sport will begin to overheat if I'm in stopped traffic for more than 5 mins. on a hot day with the A/C on. I can correct it by turning off the A/C. Would a different thermostat help? If so, what temperature do I need?

 

Stay with the stock temp on a t-stat.

If it was the thermostat, you would see overheating at other times.

Check your coolant level and condition. Look for contamination such as a rainbow sheen on the coolant, which could mean a head gasket issue.

Check the fan. These fans crack. Make sure you have all the blades and that it isn't cracked so bad it flexes and doesn't draw enough air.

Check your belt. It can slip without making noise.

Check the radiator inside and out. Gunk inside and clogged tubes will cause overheating. Externally fins jammed with a billion insects will do the same.

Going beyond all that, replace the water pump. Look for signs of a worn or eroded impeller.

Have the system pressure tested to see if it holds. If not, check for leaks and again, check for coolant in a cylinder.

A failing head gasket may allow superheated exhaust gas to get into the coolant. Usually this will cause trouble at all engine speeds and loads.

Since combustion pressures are much higher than coolant pressure, you may not get much or any coolant in the cylinder, at least not at first.

 

flush the radiator, look for good flow and clean water... then go from there.

 

Thanks very much! Will follow the advice!

 

Don't forget to check your fan clutch.

 

I had a 99. I agree with the above posts.