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Discussion Starter #1
I have a 1997 ranger with 3.0 v6. It only runs hot when I'm going up a hill and on the accelerator hard or when driving over 60 mph. It's like it has restricted water flow I'm thinking. I have changed the waterpump and taken the thermostat out. Does anyone know what could cause this?
 

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Welcome to the FFO!

Basic operation of the cooling system.
During low vehicle speed the system needs radiator fan operation to move enough air. And the water pump to move the coolant through the system.

As vehicle speed increases, the system no longer needs the fan and only barely needs the water pump movement. Because air is already blowing through the radiator and near boiling water moves a lot, pretty much with out the help of the pump.

As to the thermostat, it is wide open and is NOT a factor when heated up. Coolant blows through the thermostat like it isn't there, well because it essentially is not there.

That leaves only one piece - the Radiator! The radiator has a easy job at slow speeds and when the engine is not putting out a lot of heat. It only has to remove the little bit of heat that the engine is producing. Under acceleration and at higher speeds the radiator has a bigger job of heat removal. If the radiator does not remove that heat the coolant temperature goes up.

My guess based on your post, your radiator has some restrictions either externally or internally. If external you should be able to see it. If internal it needs to be flushed out OR ... if the condition has been a long time in making on your 23 year old Ranger the internal restriction can not be flushed as it is caked internally to the radiator. Replacement is needed. The cooling system needs to be drained and refilled every 3 years to prevent a situation like this.

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Discussion Starter #3
I have flushed the radiator and cleaned the outside of radiator so I will be replacing the radiator this weekend. Thanks for the help.
 

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Post back with the results. I had the same issue with an old Econoline. Did the same thing. Until the radiator was replaced I had over heating under high loads.

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