rockauto says our radiator caps are 16 psi, so that's about the max you'll ever have in the system. higher pressures will release into the overflow tank. i think your 20 psi test is adequate.

i'm just asking a stupid question - you did install the t-stat with the sensor side down right ?

so, why would no t-stat allow more than adequate cooling, and a 180 tested t-stat hold back enough coolant flow to cause the temp sensor to read 210-220 ? the t-stat would create some restriction in flow, and also recirculate the flow until the 180 is reached.

well this is just another stupid idea, but if nothing else is discovered, and a 180 runs 210-220, then i wonder what a 160 t-stat would run at.

 

tstat is correct....yeah i was pondering the 160....do you think that my rad could be partially clogged?

 

not to hijack but more to help im having an identical problem, and i would help you if i figure anything out...as for me.....the truck idles a perfect 195...driving around country roads at 45-50 mph it does 195 no matter how hot or cold outside...but asoon as a load goes on the motor, hills...highway...etc...it stays between 210 and 220 and it never did this before....the only thing i read from this thread was you said you cant spin your fan by hand? i can spin mine very easily.

 

I had the same problem with my 88 xj, in the winter it would do just as you described, when spring and summer came it would overheat even on short runs. I took my radiator out and found a blanket of crap in between tranny cooler and rad. that otherwise could not bee seen, also took it out and ran a chemical cleaner through it. It was full of silicone. I also had a bad fan clutch which "felt good" but was still bad. As far as the t-stat, on this engine I couldn't tell you, but my XJ would not run right without it. It needed the t-stat to get up to operating temp.

 

fan clutch should be a little sticky feeling. you should be able to spin it by hand with just light resistance. if you give it a pretty hard spin, it should turn a round or so and stop. another good test is to watch the fan as an assistant turns off the truck. when the engine stops, the fan should stop within a few more spins. it should not freewheel.

bottom line to all this. these clutch fans are supposed to be semi-coupled to the motor. if its too loose, then you don't get enough air movement when the truck is not moving. this mostly comes into play in hot weather and with AC on.

 

well sence we are on the T-stat subject, i have a 160 in mine, itll run 160 for alil while but will slowly go up to 190-220(depends on if im moving or at a stop light).

 

if i give my fan a hard spin itll go about 1/2 a turn......earshot, was yours hot b4?

 

so you didnt find any leaks with the pressure test? If not, you could remove the radiator and hose it down...it may be clogged...

 

nope, no leaks.... i hosed it from the front and back and it looks pretty clean

 

i took off my lower hose to see if i could turn the blades but i couldnt feel anything with the screwdriver, but the spring in my bottom hose was broke, i cut it open and it was broke in 7 pieces.....got a new hose and still runnin hot.........with the truck fully warmed up should the top hose be hot or just warm.....it was only warm, you could hold it with no prob......guess next step will be water pump?