So I had a slow coolant leak somewhere but could not spot any evidence, even with a borescope. It would be a while before I could get the car on a lift to look from below so I figured buying a new radiator cap was an easy thing to try. The new cap is marked 140 kPa [20.3psi] while the original cap is marked 120kPa [17.4psi]. 17psi is already a pretty high pressure to run, but I figured that Jaguar had just superceded the old lower cap so I put it on. Ten minutes of driving later the radiator unloaded in a parking lot. After a tow to the dealer I find out that the hose on the bottom of the expansion tank popped off. Not clear how a hose 'just gets that loose' after any amount of driving but there it is. I figure the higher pressure pushed it over the edge. Anyone else have a hose 'just come off'?

Sadly the service mgr was not particularly knowledgeable about why it might have come off and generally gave me the impression he didn't care. Also listening to them talk disparagingly about other customers while I was waiting was not encouraging. While I was starting to like the service department, they are showing themselves to be a steroetypical dealership more interested in getting paid than solving my problem. That is their prerogative, it just does not win my loyalty.

SO, does anyone know why the new caps are higher pressure? Any techs out there with info on this? Anyone encountered a TSB on it?

cheers,

TonyL

 

I don't recall hearing that the pressure had changed so I wonder if you've been given the wrong one?

But... there should not be so much pressure that the cap would have vented (either the previous or current cap) unless there's a fault. To blow off a hose, particularly the one you mention which people generally have trouble removing, is worrying.

Brutal has posted that you can run with the cap loose so maybe try that?

 

I know this is an older thread, however I just bought a replacement radiator cap from Jaguar in New Rochelle NY, (Larchmont Jaguar) Very very nice people. The old cap is marked 120 kpa. The new one is marked 140 kpa. I was told by the parts manager that Jaguar has upgraded this part number three times since its introduction and he believes that the higher one is correct for the vehicle. I will try it and see how this works as I am having overheating problems.

Best to all.
Rob
XJ8 2004

 

I think that the cap that you got was defective and not venting at all like my old one that cracked my thermostat housing and heater control valve, the 20psi won't break things, if it releases pressure above that. When I first got my car the main coolant hose on top was hard as a rock when the car was up to temperature, I thought that was normal. After getting a cap that actually works you can easily squeeze the hose. How loose can you put the cap on and have it not be too loose and still work right? Where's Brutal when you need him?

 

Rob,
just keep in mind that the right thing to do before installing the higher pressure cap is to at least pressure test the system at the higher pressure. I got very lucky when my hose blew where it was easy see.

cheers,

TonyL