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This might be a common issue, but just tossing it out in case it helps someone.
My wife was heading to Denver last summer (we are Vancouver, WA) to visit our daughter and grandson. Decided to take the XJ (2008 X358). Left early in the morning, got a call in the afternoon, engine died. She had it towed to Caldwell, ID - about the closest town, and I got out of here that a hose was broken off of the header tank, car had shut down.
I had a header tank overnighted in - was a bit surprised at the easy availability in the aftermarket. Headed for Caldwell, hoping for the best - no such luck. Installed the header tank, got it to run, but it was clearly down a couple of holes, and the oil and water had managed to co-mingle. Rented a trailer, brought it home, into the garage it went. Next, the dilemma - try head gaskets, or replace engine. Jaguar wanted $20K for an engine - guessing they sell a lot of those? Head gaskets and bolts weren't cheap - and there would still be some uncertainty; so went with an Ebay engine, for $1000 or so. Engine looked a bit tatty on the outside, was a little worried - but replace timing set, shaft seals, cam cover gaskets, etc - it was absolutely immaculate inside. Installed it, car runs great, had no problems since.
Only reasons for posting are:..
Initial failure was the header tank vent line nipple. When I replaced the engine, the low coolant sensor and warning light were working..
My wife swears that she did not notice it overheat - I was not there, could not say She did say, however, that there was no smell, no rough running, A/C was still working.
I would infer from this that the Jaguar ECM did not provide much protection - for an overheat, I would have expected. A/C pulled first, then full heater selected, then power reduction, limp mode, then "Camel" mode - alternating cylinders disable, then shutdown. As far as I can tell, none of this occurred.
When I replaced the engine, many of the other plastic cooling system parts were very brittle, on the edge of failure - a couple broke in removal.
I replaced pretty well everything plastic and rubber in the cooling system.
Lastly, I made the right decision in replacing engine. I was making room in the garage to do an LS3 swap on the XJS, tore the engine apart, found this -
So - maybe best to check cooling system plastic parts. My car had about 80K on it when this occurred. Was originally from Phoenix area, I had had it for the previous three years. Opened the hood before the wife left, checked fluids and so forth, but that's as far as it went. Sorry, no pic of header tank, left it in Caldwell.
A valid point. I just touched the vent hose on the expansion tank because it looked a bit slanted when the nozzle immediatly broke off and coolant sprayed through the entire engine compartment. Luckily the car stood in the garage.
I am sure that the high coolant temperature triggers visual and audible warnings. The problem could be that the sensor does not register the increased temperature because it is very quickly no longer flushed by the coolant.
AJ34 engine failure - header tank failure.
