Hi everyone - I have a 99 XJR that is building up massive coolant pressure and not circulating through the system. I replaced the thermostat already and that made no difference. It begins to overheat after 10 minutes and one radiator hose is hot and other is cold. What could be stopping coolant from flowing through? Should I buy a new radiator? Maybe just remove the thermostat completely? Please help.... Thank you.

 

Have you emptyed the coolant for any reason ?
If so have you bled the intercooler ?
I fear you may need to get the coolant tested for combustion gas leaks (blown head gasket)

 

Your water pump could be pooched.

 

Yep, perfectly sensible observation - don't worry about gaskets 'til you've checked that suggestion.

 

Thank you. I found out some idiot put stop leak in the system... I'm taking to my mechanic.

 

Before I take to the mechanic, should I try to drain the system and add in Cooling System Flush?

Will a bad water-pump do exactly this?

 

When you replaced the t-stat did you bleed the coolant (as well as remove the bolt from the S/C to bleed any air?

It sounds like a couple of possibilities:
1. system not bled- air pocket by water pump, not able to circulate the coolant
2. bad water pump- I would think you would still have a "warm" side and "hot" side
3. system blocked by stop leak- possible

My vote is air pocket.

Did you have any leaks prior (like the front of the engine)?

 

Yes! Yes! Yes! I reaplaced a hose and replaced the thermostat and did NOT bleed the system. This explains it all. Thank you guys! Now... How do I bleed the system? :-)

 

As it's an R you've a big allen type nut on the intercooler crossover on the top of the engine a nifty way of unscrewing this to top up the system and bleed is to buy a couple of nuts that fit into it and lock them together onto a bolt. Then unscrew with a spanner on said bolt/locked nut combo.

Relatively straightforward to bleed these cars, turn the engine on, switch the climate control to full and hottest setting to open the heater valve and matrix.

Fill the header tank slowly and squeeze the top hoses as you do to burp the system. Once the header is full, no bubbles, it's time to open the IC plate and top up into there. It may not need much. Button it up and see how it runs then.

If it's still happening, maybe check the header tank hoses, sometimes they get criss crossed and create this issue. And also try and run the car without the T stat. If it's still overheating then a sniff test is in order... You did put the T stat in with the nipple pointing at 12 oclock, not 6 yes?

 

It really should bleed itself if you have a thermostat with the little jiggle valve at the top and installed in the right orientation. But you need to have the heat on all the way to high, and squeezing the radiator hoses repeatedly may help.

 

The intercooler won't self bleed. As Sean says take the big hex nut out, turn on the ignition then pour in coolant until it overflows.

 

You guys have been so helpful. Thank you very much for all the instructions! I will work on the car this weekend and report back. I wish I could buy you all drinks at the bar!!

 

How about a radiator flush?

 

XJR coolant drain, fill, bleed instructions and illustrations extracted from the JTIS21 Shop Manual (covers 1998 to 2003 XJR models):

https://www.jaguarforums.com/forum/a...-bleed-r-i-pdf

Seems like the shop manual has a few more steps to perform.

Jim Lombardi