I have an 02 XJR with 158K miles. It burns anywhere from half a quart to a quart of oil per 1000 miles. I can live with just a half a quart per 1000 miles but a full quart is more than I would like if there's a way to reduce it. I have used full synthetic 5W30, full conventional 5W30, and semisynthetic 20W50. Any advice?

 

Two main reasons are damaged piston rings and worn valve guides as well as leaks of course.

You can do a compression test that will give you a clue. Do it twice the second time with a squirt of oil in each cylinder.

If compression is significantly better then you have worn piston rings.

If no change then possibly worn valve guides.

 

+1 to John's response and to see if your burning it or blowing it out, your plugs will either have a oily residue and/or carbon build up on them.

 

Try Liqui-Moly Motor Oil Saver. Works wonders on busted valve stem seals.

 

Tell us if your leaking oil.

Also, the drivers side valve cover part load breather may be plugged up. Do a search on the procedure for it. It’s not hard as long as you don’t break the breather tube. The PL breather being plugged shut will cause oil leaks. It may not be “Thee” fix, but it’s a step in the right direction. I’m also going to add to the valve stem oil seals being bad at that mileage.

 

No oil leaking.

 

Inlet valve guide seals tend to wear and also harden and then let oil into the inlet manifold where it's burnt. Clearly replacing these guide seals is not trivial, but still better than dismantling the engine to replace piston rings. If you think your oil consumption is high, the original Jaguar XK six cylinder engine would burn a pint of oil evey 250 miles. Jaguar made many attempts to stop this, but it was only really put-to-bed when seals were put onto the inlet valve guides. I remember replacing mine when I did a top-end overhaul of a 2.4 litre.
Of course you also need to do a pressure test for each cylinder to check the piston rings are sealing. My money is on the inlet valve guide seals, though.

 

+1 What Fraser said about valve stem seals. If you made it as far doing the valve guide seals then by all means, for a little extra work pull the heads, have a proper valve job, valve adjustment and new fond power added along with MLS head gaskets for a little extra bump in compression. However, just need to verify that the rings don’t have a severe amount of blow by first.

I did all that when my 98’ XJR had 234K on it 6 years ago and now it has 261K miles and still running strong.

 

Would still highly recommend the Liqui Moly product to extend the life of the valve stem seals before servicing is required.

Read some of the reviews, particularly from the BMW V8 guys.

 

I already ordered it