[Hemicolt]

As long as there is nothing wrong with the tune, in the engine or bad clutch on the fan, you should look at these guide lines.
If your car runs hot at low speed or idle, but runs cool driving at highway speeds, it should be a lack of air flow as the problem.
Running cool at idle or low speed but running hot at highway speeds will suggest that the coolant is running through the system to quick and it doesn't have enough time to cool. Several things can be looked at to fix this problem. Pulley sizes can be one as the water pump may be spinning to fast. Also, installing a 165 degree stat. doesn't help with this problem. If your car runs at 185, this will mean a 165 stat. will be wide open at all times and the system will have less restriction. Using a higher temp stat. will insure that the stat. is not open all the way and will provide restriction which means the water slows down at highway speeds. Does your car have a cowl induction hood? If so, is the scoop sealed off from the engine compartment?