Can the air get through the radiator?  Take a flashlight and have someone
hold it behind the radiator between the fan blades.  (you may want to shut
it off first).  Then stand back a few paces, you should be able to see that
light through the radiator AND condenser.  If not, you need a disassembly
and cleaning of the exterior of these items.  A pressure washer can help,
but be careful not to bend the fins on either item.  You may have to remove
the grill, to get a good straight shot.

"biker" wrote:     (1992 E150 Van Conversion 302CI with trans cooler)

I pull a pop up trailer and whenever the weather is very HOT & very
HUMID the motor overheats.    I have cleaned out the radiator,
flushed & changed the fluids, changed the thermostat, put a new
fan clutch in, changed the radiator cap, and checked to make sure
the fluids are moving when running.   But it still overheats only when
it very hot & humid out. The 80's are fine, 90's it overheats.
What am i missing, HELP?
________________________________________________________

Humidity is not the problem - heat exchangers (radiators) work
better in humid conditions than in dry conditions.

Some possible solutions:

Remove the radiator and have it boiled out by a radiator shop to
remove deposits that won't respond to retail flush chemicals.

Buy a new radiator with an extra row of core tubes.

Replace the fan clutch with a fixed spacer.

Use a hose to flush the dirt out of the radiator fins, and the AC
condenser fins if so equiped.

Be sure insulation pads in the engine compartment do not restrict air flow.

Do not use 100 per cent coolant in the radiator.    A 50/50 mixture
of coolant and water transfers heat more efficiently.

Replace the water pump if needed.

Good luck.

Rodan.