If it was overheating on the highway, the fans wouldn't have made a difference. There is another problem. I'm not saying the fans shouldn't have been on, but at highway speeds, the air flow through the radiator is more than the fans can produce. Have you replaced the thermostat? Also, with the engine cold, remove the radiator cap and start the engine. If coolant shoots from the radiator, chances are you have a bad head gasket.

Answered by Jacobandnickolas (expert)
57,318 answers provided

Make sure wiring to fans is hooked up. Do fans run with AC on?

Answered by Docfixit (expert)
18,458 answers provided

Air in cooling system is the most common cause of overheating after repairs.

Was the system bleed of air after repairs?

Answered by KHLow2008 (expert)
39,964 answers provided

HOW DO I BLEED AIR FROM COOLING SYSTEM

Response from JCROSBYMS
2 questions asked

Top up coolant.
Turn heater to maximum.
Run engine for 5 minutes with radiator cap off.
Add coolant if necessary.
Stop engine.
Add coolant if necessary.
Start engine and if level does not drop, close radiator cap.
Run engine till operating temperature, radiator fan comes on.
Allow to cool and recheck coolant level.
Add coolant if necessary.
Repeat process if coolant level is very low when rechecking.

Answered by KHLow2008 (expert)
39,964 answers provided