Overheating at High Speed and High Temp

[Ranger254]

My 99 Ranger 4x4 Runs great except when the outside temp gets above 95 and I'm doing 70 on the interstate with the A/C on. Temp guage climbs to max and I have to turn the AC off, open the windows and slow down a bit. I've flushed the system, replaced the water pump and thermostat. It'll idle all day like that without a rise of temp...............any help?

 

[thegoat4]

Have you cleaned off your radiator?

 

[shadetree]

Make sure you have the correct radiator cap, and it is sealing as it should. How did you flush the system? You can't flush a plugged up radiator. It has to be cleaned manually.

 

[Big Jim M]

FAN CLUTCH!! Clutch, clutch, clutch..
Big JIm

 

[shadetree]

FAN CLUTCH!! Clutch, clutch, clutch..
Big JIm

He doesn't need the fan at hiway speed in most casesshady

 

[MAKG]

FAN CLUTCH!! Clutch, clutch, clutch..
Big JIm

Not this time.

The symptom of a free-spinning fan clutch is overheating at very low speed and at idle. This one is at high flow conditions, so somehow "cool" isn't getting from the huge airflow through the radiator back to the intake manifold.

THIS one sounds like a restricted cooling system, either a plugged (or partly plugged) core or a collapsing lower hose, or a stuck thermostat, low coolant, etc.

To test the radiator, warm it up solidly, shut off the engine, and feel the back for cool spots.

If you have an automatic transmission, give it a stall test. If it's slipping, it will make a BUTTLOAD of heat, especially on the highway.

Another more remote possibility is a failing or overcharged air conditioner.