I have a 88 4.0. With 160k. She likes to get pretty close to the redline on the temp gage, only when I'm driving past 65mph on the freeway. When I'm cruising right at 65 it stays at about 190 degree. Anything past 65 it slowly starts to creep up. Around town she does great even cooler then 190. If i turn the heater on it dramaticaly helps. So far I have charged the thermostat made sure the Rez was full and bleed the system with the rear temp gage sensor. I know she shifting into over drive. Also the small fan does kick on.

 

Replace the waterpump. Mine did the EXACT same thing when I bought it. I replaced the w-p and problem solved.

 

I completely agree. The water pump is the primary suspect here.

The vanes on the pump deteriorate with age and miles.

Be sure to purchase a NEW water pump. NEVER go reman/rebuilt when purchasing a water pump.

And while you're at it, toss in a new radiator if it is long in the tooth.

 

whens the last time the fan clutch was replaced

 

My 95 did that and it was the radiator was plugged internally.

 

A bad fan clutch would cause problems at low speeds. Over about 40MPH the fan really has no effect on cooling. Not a bad idea to replace it if it feels weak though all the same.

 

Im not sure when the clutch fan has been replaced I just bought the car 3 days ago. I don't have any over heating problems at low speeds only on the freeway going up hills. I think Im going to try the water pump next seems like a pretty easy project.

 

Put a new 195* thermostat in while you're at it. I'm only buying them from the dealer anymore. Too many problems with the aftermarket ones. Part Number 83501426.