Hi I'm new here. I have a 95 xj and sorted my heat problem.
It started after I serviced the cooling system which appears common from US forums.
This got me thinking about 70's mopar mussle cars which had common dramas with water vapor lock in the blocks.
Tried this... Got xj hot carefully removed radiator cap jambed a coke bottle full of water on top of the radiator inlet and pumped the top hose a lot. Fitted in 3 more liters of water!
This sort of fixed it.
Stage 2
Total flush. Put radiator flush in system turned heater on ( important!) and ran it for 20 minutes. Drained system, took off top and bottom hoses and thermostat, flushed in both directions at high pressure for probably an hour same with radiator. Got a heap of brown goo sort of like algea out. Got a hose joiner ( about inch and a quater i think) cut the top hose in the middle of the straight section in the middle and fitted the joiner with hose clamps. Drilled a small c/s self tapper screw in the top of the joiner
Reasembled all and filled with coolant.
Over the next few weeks just undid the screw half a turn straight after a drive and let some air out with Engine hot and turned off. You have to remember to keep the radiator top off tank full as every time it cools down it's going to suck a lot more water in
In answer to probable questions.
No the screw does not leak, you just be gentle with it and the bite at the counter sink keeps it sealed, I did this a year ago and no probs.
The problem was most evident going up a steep hill the temp would go straight up.
This is the problem I think, glycol can promote algea growth, this is why manufacturers suggest radiator flush once a year. With a older car with a poor cylinder head design you can get algea blocking the water flow, if you don't flush the heater as well there if always more algea to grow.
Being totally full of water is not critical but with a very long six cylinder with a fairly high mounted water pump I think what was happening was the system was down about 3-4 liters when just doing a standard fill. When I was going up a step hill the water flowing to the back of the block was exposing the water pump to the air in the block and causing pump cavitation ( this is when the pump impeller grabs some air and just spins this air and steam) so instant over heat as you effectively have no pump. I took the pump off and checked it and there was cavitation pitting on the inside of the pump but not enough to affect it's performance.
Stage 3
I still had a lot of under bonnet heat though the XJ was not over heating this turned out to be cracked headers and a leaking exhaust manifold gasket, I took the headers off and welded them up ... temp fix as they will crack again eventualy but ok so far
bolted all back together and it's gone from the top of the bonnet being to hot to hold your hand on, to normal road car temps !
Hope this helps any jeepsters out there with silly cooling problems
