Xsivelybad

1999 Jeep Grand Cherokee Laredo 4.0 6cyl
I was on my way home and the jeep started overheating. As soon as I noticed it I stopped and turned it off. got it back to the house and I went ahead and replaced the thermostat. Still overheating. checked fans out both working. Flushed the radiator, pressure tested no leaks found. Bypassed the heater core just in case. STILL OVERHEATING!!! Don't know what else to check or do. HELP ME!!!!

pwb

Water pump?

Xsivelybad

Water pump is working because there is flow. Also, it is not leaking from the weep hole.

tiwvr1

Alot more info needed, when does it over heat? Driving or idleing, what did the coolant look like, did u put the thermostat in right, check the radiator on the battery side, see if the cores are rotting out.

And by over heat, what temps do you mean?

freegdr

0331 head issue?

Xsivelybad

it overheats on a trip around the block or sitting still. The thermostat is in properly. The coolant looked green like coolant. How do i check the "cores"?

Xsivelybad

A little more. I realized recently that the e-fan was bad and after testing it I replaced it. Works great now but the truck still over heats. I have the water pump clutched fan and a e-fan. RED LINE temperatures. STILL OVERHEATING.

PatriotGT

are you sure the gauge is reading correctly?

Xsivelybad

tested temperature with a temp gun and the gauge is pretty damn close.

dave1123

Here's something you can try. With the engine dead cold, start it up and only run it for one to two minutes. Take the rad cap off. Is there pressure in the rad? If there is, you have compression leaking into the system, for what ever reason, be it a blown head gasket, cracked head, cracked cylinder barrel, whatever. If there isn't pressure with cold coolant, I would look for an obstruction somewhere or a broken waterpump impeller. Also check the lower radiator hose for collapsing internally. I have seen 4.0's with shattered pump impellers before, usually plastic ones. There is only about 1/16 inch between the impeller and the first clyinder barrel. You may be getting "flow" only because the coolant is boiling.

Good luck with this. 4.0's are reliable and just about bulletproof, but they are torque engines, not drag racers.

freegdr

pressure test system

sthon

Wouldn't feeling the upper radiator hose be sufficient in checking for pressure? Seems much safer to me...

freegdr

deff would make more sense

tiwvr1

run it with the cap off, Wait till the engine is cool to remove cap, run it and see if bubbles keep coming up. Also if u look at the rad and see the cooling fins coming apart, then the lower part of the rad is probably clogged.