Trying to get info for a friend.

Here is the situation, he has a 74 cj5, with a 232 eng, he's replaced the thermostat 3x, new radiator, hoses, shroud, all new top and upper end, timing is dead on, ...When the thermostatin it overheats, take out the thermostat, it runs cool. Put it back in, overheats. Waterflow all looks fine,,,,,he's had many a jeep but this thing is a bastard. Maybe the waterpump????? Any advice would be helpful.

How's the raditor, how old, has it had work done to it before ?

Try another thermostat.

Flush the whole system.

If there is a by-pass hose, check to see if it is blocked.

How long does it take to overheat?
What's the CJ doing when it overheats? Highway driving, trails, etc.
Has the cooling system been flushed? Is there coolant, or just water?
Is the bypass hose there?

Since everything looks new. Here is a dumb suggestion, but ya never know. Is the thermo installed right side up?
The next thing is the water pump.

He has a new radiator, has tried a 4th thermostat, even tried it backward, it has coolant, driven on the highway. It went about 2.5 miles before it overheats.

air in the system? try drilling a small (3/32?) hole in the top of the thermostat flange if it doesn't already have one. Make sure it is installed up to let the air thru.

scott
jusy a though

Has it ever overheated bad enough to warp the head? (really HOT!!) You can test it to see if your getting exhaust gasses in the cooling system.

:confused: does it have the stock fan or an aftermarket electric fan ? If it is stock I might check and see if the fan clutch is working. There are a couple of tests you can do.
GOOD LUCK:beer:
IF IT IS ELECTRIC USE A TOGGLE SO YOU KNOW IT IS ON!!

Sounds like an air flow problem.
Pull the hood & see what happens on the highway.