what exactly is a high mileage jaguar 5.3L V12 engine?
and how often does the head gasket go on the V12?

my car has 160,000 kilometers, which is 99,419 miles.

ps I have done everything possible to prevent overheating, when I take it out for a run at high speeds, I run it for awhile at slow speeds with the hood cracked, then when I park it I prop the hood open for at least an hour.
I have installed an all aluminum after market radiator, all new belts, new hoses, fan, fan clutch, spark plugs, wires, distributor, mechanical advance was renewed as it was seized, timing was set at 18 degrees, new thermostats which show the temperatures about 2/3's the way up to the N, or normal, rarely does it get to touch the bottom of the letter N.
And I change the oil regularly, I use conventional oil, 20/50 right now for summer, and I only burn high octane gas which is 91 octane with no ethanol, but lately another gas station has installed another grade of gas, it is octane 94 with no ethanol. Is octane 94 to high of octane?
So does anybody have a V12 with 350,000 miles on it? Or by that time does it need a rebuild? Donna

 

Well you're doing all the right things, although lifting the bonnet is a bit OTT to be honest. By wires, I assume you have replaced the looms around the engine and fuel injection, and by hoses, this includes the fuel injection hoses on the fuel rail. Engine fires can occur if old fuel piping splits. The mileage is not a great deal for the V12, assuming it has always been looked after. No problem using 94 octane fuel, just the extra cost.

What car is it, XJ saloon or XJS, and what year ?

Suggest you post into the forum for your model for more info.

 

Most V12 Jags are relegated to occasional use nowadays so there's little opportunity to accumulate ultra high miles. I've not heard, personally, of a 350k mile example but I'm sure there are 200k examples out there.

100k miles is still young for a V12 if it has had regular oil changes and not overheated. Of course I'm referring to the engine itself, not everything that's bolted to the engine :-)

Head gaskets do fail on V12s but, from what I've gathered over the years, not on a regular basis (as opposed to some other Jag models where head gasket failure was simply a matter of "when", not "if")

Cheers
DD