OK. Read a lot on here about this, but still hoping for a better solution. Here is my problem:

2002 F-150 V-6. overheats after 30 minutes. Always.
Tried new thermostat, cap, and flushing radiator.

Only solution that works for me, and not practical when over 100, is to turn on the heater. Temp stops rising and goes down, no matter the driving conditions. I have tested it lots of times, even pulling a horse trailer.

Any hints on what I need to replace?
I have read to replace radiator, fan clutch, water pump, ect.

Just really dont want to start throwing 100 bills at it, unless it will work.

Thanks

 

Best thing to do is pressure test the cooling system with a leak down test. This will tell you if there are any leaks.

 

x2 borrow one from Advance Auto and pump it up to 15 psi and make sure it holds for an hour or so. The 4.2s are pretty notorious for blowing head gaskets and heads cracking and warping hopefully that's not your problem. With the truck hot touch the radiator near where the upper hose is and where the lower hose is, if it's hot at both the entrance and exit your radiator is fine, if it's hot at one and cooler at the other it's plugged somewhere and you need a new one. If those things are good I would replace the water pump and thermostat. At that point it should definitely be taken care of but if not it could be the fan.

 

Have you checked to see if your losing coolant. I had this problem and it turned out the hose going into my water pump wasn't tight and it was leaking coolant out. I'm sure you've checked this already but sometimes people overlook the simplest things. Just thought I'd throw that in there.

 

By using the heater, you have gained another means to expell heat from the coolant. If engine is holding temp by doing this, seems to me you have solved your problem, your system is not functioning to its maximum. As was stated above (which is near impossible with AC) place hand all around fins of radiator and look for cold spot.

Things we know about cooling systems: 1, T-stats set MINIMUM engine temps, not MAXIMUM. 2, Heat transfer or ability to remove heat from coolant needs air flow across radiator fins and complete flow of coolant thru radiator tubes.

Radiator flushes are a joke and a complete waste of money, do more harm than good. A radiator shop needs to remove one of the tanks and rod out each tube to ensure proper coolant flow.

Getting back to air flow across radiator, fan clutches aid in increasing air flow across radiator in City driving, ram air does all the work in freeway driving. Hope this helps.

 

Are you talking about trying to flush a plugged radiator or simply doing coolant flushes? Because coolant flushes are absolutely necessary, not only to prevent nasty brown gunk building up in your motor and radiator but coolant over time breaks down and becomes less efficient. Gold coolant in the 2002+ trucks is a whole lot better and doesn't need to be flushed untill 100k, but green should be done every 30k. Really old green coolant is completely disgusting and rusts the coolant passages in the motor.