Oil Pressure

I wouldn't do a thing until/unless you verify the true pressure with a wet gauge. It could be an electricsl fault -probably a bad sender or wire. The gauge will peg if a chafed wire shorts.

Pete

Bernie
The typical symptom of worn valve guides occurs when you start the car after it's been sitting overnight or an equal period. It will smoke - often quite badly, as it burns the oil that has leaked past the guides into the cylinder. Once that is gone the exhaust looks more normal. I have some doubts that leaking valve guides would account for the level of oil consumption you observe.
You can have good compression and bad oil control rings - worn, gummed up, incorrectly installed etc. My '68 E type when first purchased (in 1972) went through a quart every 125 miles. No smoke but a lot of dirty black stuff out the pipe even when hot. Original owner had babied the car when new - had glazed the cylinder walls - you could still see the honing marks through the glaze. Once glaze removed car ran fine. Not suggesting that's your problem but i would suspect it's an oil control ring issue.
As to excessive oil pressure - XJ6's had a stronger spring in the pressure relief valve in the filter block, and ran at 60 psi hot - 80 psi cold. Wonder if somebody put one of those springs in. I autocross my E Type and run an XJ6 housing - I just installed a 100 pound gauge so it all works. As oil pressure is totally controlled by the spring I doubt if you are hurting your engine doing this. We ran 100 psi in our E Type race cars with no issues.

Bruce

Will also try your suggestion...thanks for that idea with the 3,000 rpm coast in...that should "get em while they're hot"

The testing I was referring to above was a valve diag - it was a "vacuum test" - not sure if you were referring to a wet/dry cylinder compression test

Bernie

Bernie, you could have good compression and the guides could still leak. If the valves themselves are seating well they will not let compression loss when closed. Try running the car down the road after it warms up. run up to three thousand rpm and turn off the ignition, coast to a stop. pull the plugs and see if they are light brown (very good) if they have oil on them you will know what your problem is

good luck

Bruce

thanks Joseph...I agree completely with your thought process on the valves but the vacuum test I did on the valves was straight line perfect at all rpm's...

and then there is the motor performance - very strong smooth running car...something doesn't add up...

I am going to next inspect the relief valve...

Bernie, the relief valve is pretty simple. A brass valve held against a steel seat with a spring. If the spring gets weak the valve opens at a lower than 42psi, if the spring is stretched or shimmed or a stiffer spring is used, the oil pressure will be higher before opening to return to the sump. I have seen debris trapped under the valve when open, that didn't let the valve close. Resulting low oil pressure at idle.
Cheers Tom

Bernie,

I'd suspect oil consumption is worn valve guides.

Thomas,

Thanks for the info on the relief valve line...I will remove and inspect shortly as I am just about up to changing the oil - I've been conducting (shall I say) some "experiments" with Marvel Mystery oil with some interesting results ... but it is about time to get it out of the sump.

Do you have any knowledge of the pressure relief valve itself in terms of it's operation (or potential failure to operate correctly) or is it more or less a no brainer type of thing that if put together correctly always works?

My 68's oil PSI behaves somewhat similar to what Bernie describes going off scale high especially on colder days but then comes down into the 40-50 psi range once the oil gets warmed up thoroughly . I also run Castrol 20/50. I pulled the spring and valve several years ago but did not see anything obviously wrong so I put them back in without doing anything. Since then I always just thought it was on account of the oil being thicker when cold. I too hope to hear if this is something to worry about.

David Barnes
68 E-Type FHC

Bernie, John is correct. All the XK engines have a pressure relief valve that lets the excess oil pressure drain into the sump. There is an oil hose directly below the oil filter housing connecting the oil relief valve to the oil sump. Oil pressure was set at the factory at 42 psi. Anything more is directed back to the sump. This is accessible from under the car. No need to remove the housing, just the oil hose & unscrew the hose fitting from the housing. Should only contain a spring & brass valve. I have seen washers stacked on the spring to increase the pressure. Also check your dip stick. I have seen bent / curved oil dip sticks that caused them to read low. Adding too much oil will cause excessive consumption. Good luck.
Cheers Tom

Not sure about the 4.2 but my 3.8 has an oil pressure relief value which is located on the oil filter assembly. It is a spring and ball (I think) and will relieve the pressure if the filter is stopped up. If this is working properly you should never show too much pressure on your gauge since this relieves the pressure before the oil pressure sending unit.