'91 4.0 - Recent (5 months ago) rad, cap, tstat, watr pmp, hose replacement and flush. I know the heater core valve is going out. I have a replacement. But it is running VERY COOL. Will not get to normal op temps at all. Its 10-20* here but it should. Think tstat is stuck open??? Or could core valve cause this?

 

10 to 20 degress has alot to do with it i bet

 

Thats what im figurin. Time for some good ol cardboard fabbin!

 

It should reach t-stat temp or very close regardless of ambient temp. Might want to shoot a temp gun at it to verify coolant temp and gauge.

 

i know you seen the tractor trailers with the covers over there grills to bring temps up

 

Think its stuck open? Today is warmer and it actually hit 210. If its stuck open i should have good pressure and some heat in upper hose before reaching temp correct? Best place to shoot temp gun to read that? Lower hose on tstat housing?

 

Yeah i would hide mine a lil better. We used to have to do that to a couple of service vans for electrical outfit i worked for.

 

It could be.....one way to find out and while it's out u can test it in a pan of water on top of the stove using a cooking thermometer. Pressure rises throughout the system as temp in the motor rises, presuming the rad cap is good. Shoot the temp gun at the t-stat cover....should see temp rising shortly after motor starts.

Big difference between big diesel rigs and the XJ. 1st, diesel burns cooler than gasolne and 2nd (main reason) big rig rads are way over built/sized and the XJ rad is way under built/sized.

 

I would assume the problem is in the thermostat. In Truckee we average negative Temps in the winter time. At the most when I'm driving to work at 4 AM in -0 to -15*, my temp gauge only drops too 200*, and the heater still stays nice and warm.

 

I get temps between 200-210 on housing. Elec fan doesnt kick on. Top rad hose is hot. ????

 

You possibly have a thermostat that is defective. I only buy them from the dealer anymore. Part number 83501426.

 

What t-stat did u install? Was it a "fail-safe" maybe?

 

is the bottom hose cold or hot? it should be just about as warm as the top!!!

 

Its 50* here now. Should be hot. Gonna swap stat out later. See if that fixes it. Other than that any ideas???????? Swapped out heater core valve already. Didnt think that would have anything to do w/ it.

 

Nope. Learned that the hard way. Its a stant.