my f150 is overheating, the problem is it is not loosing any coolant and only overheats in heavy traffic, has efans (flexalite), lighting radiator, changed to new water pump (not OEM)... I can leave the truck idling all day and temp gauge never moves but when doing heavy traffic with ac on truck overheats... outside temps about 110 here in imperial valley... the radiator was cleaned last summer, when I sent radiator to clean, changed thermostat and radiator cap with OEM parts... on highway speeds does not overheat unless im going on really step hills... last time it overheated was on a wash uphill on the Baja desert... I stoped for a beer without shutting the truck and temp back to normal... already took transmission out of the equation with race tranny cooler and bypassing the OEM cooling for it completely...

hope anybody can give me a clue... thanks in advace

 

From your description it's lack of total cooling capacity.
When the motor is called on to make more power it makes more heat.
If the system can't get rid of it, the average system temp rises.
110 degree heat makes this even worse.
Are the EFANS large enough?
The radiator may still be down on flow capacity.
There is not much else to cause it.
Good luck.

 

Is the thermostat the stock 192*-195* temp? If not, that's a potential problem.

 

Are both your efans working. I found that I had fried the controller on my high temp fan and it was not coming on as a result. First confirm that. Depending on how many miles are on your truck your rad may be done. Just because it looks OK on the outside doesn't mean it is not clogged and corroded on the inside reducing the amount of coolant passages that actually flow. If it turns out to be the rad it would be a good time to upgrade to a dual core for extra cooling capacity.

 

Running electric fans on the highway reduces air flow through the cooling stack, and can burn up fan motors

 

both fans are running normal, the thermostat is the oem recommended 192, the efans are the flexalite monster 270 direct replacement... the radiator is a lightning radiator (bigger core) and was cleaned professionaly (tore apart and cleaned inside core)... the water pump is a pepboys replacement...

will look at the radiator and will install the shut off switch for highway speeds thanks for the pointers.... also thinking about buying oem water pump to be sure...

 

I believe the V10 water pump and the cobra water pump will work. they are higher flow. you just need to know if its the short or longer version. I upgraded my radiator with the 2 row from summit. O.E. had a 1 inch core and the 2 row was 2.5 inches. it's more than twice as wide and made a huge difference. If you have a programmer that cranks timing it will also generate more heat. Back flush the motor via the heater hose up front too. A old radiator hose and even some new hoses will colapse reducing flow. Good luck