I know miles aren't everything on a car. But generally with these jag xj6's series 3, how many miles have you guys seen them go before they start hitting a rough point and may need replaced?

 

Mine has a known 150,000 miles on the clock + a number of unknown miles from a previous owner (transmission transducer was out for who knows how long). Engine, if taken care of, seems indestructible. The leaks will get you first. It will leak like a sieve first and if it dies, it would be because of neglect.

 

Don't be surprised at a head gasket failure at any time over 100K miles. Other than that 150-200k miles should be doable.

Cheers
DD

 

Our S3 6 cyl had 320000kms when sold, and the current owner, next suburb, has had it 10+ years and loks after it well, and is still as made.

Clean air, clean fuel, clean oil, coolant up to snuff, I see no reason for more than 500000kms easily.

Wifes S2 Daimler 4.2 had 410000kms when a piece of #1 exhaust valve left the building. Head studs broke removing the head, so I rebuilt and balanced the sucker. Current owner reports he has topped 200000kms in his ownership (7 years now), travels interstate in it contantly, and he claims it is the sweetest thing he has ever driven/owned.

 

Mine runs like a swiss watch, and as quiet. No idea how many miles it has done and no history on the motor. It was on 600 miles when I got it but assume it had just done it's second or third time round going by the condition of the rest of the car.
I had retired mechanic with 40 years Jaguar dealer experience help me strip the IRS and when he looked over the engine he said there is no evidence it has been removed from the car or rebuilt. Not sure what he was looking at in particular, but took his word for it.

I would be surprised if I don't get another 100,000 miles out of it at the least.

 

With proper maintainence, these XK engines will clock over 500,000 miles.
A proper cooling system and an oil cooler is very important.
Keeping the head bolts torqued is important, as well.

 

Much depends on whether the engine is a long-stud engine or not. These have engine numbers with 7L and 8L. Long stud engines up to about 1981 can suffer cracking between the bores. This is because to provide coolant passages between bores, passages were machined accessed from the bores and then covered over with thin wall liners.

Once cracked, the engine will suffer continual head gasket failures, like mine did until the block was replaced with an uncracked one. Reason for this is the strength of the metal bridge above the coolant passage is lost once cracked and the block face drops slightly relieving the gasket pressure and allowing combustion gases into the coolant jacket,

This happened to my 1980, (8L block), and my replacement was a 7L block. 7Ls crack less than 8Ls even though they are virtually the same. I was told at the time, (early 90s) by an engine builder, that Jaguar tried to speed up the engine manufacturing process in the 70s by reducing the aging period after casting. Whether this is just an old wives tale I'm not sure but it was confirmed that iron casting practice was to leave new castings for a few weeks to let them "age". This allowed the stresses induced after casting and cooling to relieve following which machining could proceed. The pressing in of the liners could also induce stress into the metal bridge above the machined passage.

It is possible to cure the problem by removing the liners, and machinge the top of the block to take lipped (or "top-hat") liners that touch each other and cover the crack.

Here's a photo of a block with a liner removed : -