Recently I started seeing my oil pressure sag down to 2 or so from 6 - 8 when the engine is hot. It started happening about the time I had bad leaking in the timing chain tensioner and distributor. Those are both fixed however I have developed another leak somewhere as I still get some drops of oil on my uncercarriage. Because of the recent leaky nature I have checked my oil every 200 miles or so and it has been low on occasion but not below the add quart mark so it has never been starved for oil.

I read somewhere the Xj40's were notorious for a 'lazy oil gauge.' I suppose I should have an oil pressure test done but is this a symptom of a huge problem or is it a normal or easy fix? How bad is it for the car to run like this( it has fine pressure while moving but at lights etc it sags.)

Thanks for the help

 

Subscribed:- mine randomly does this as well. All good after an oil + filter change, solid 6, but after quite a few months it will drop when hot at idle.

Regards the 'new' leak, have you changed the valve cover gasket, I had a dribble from there.

 

If you are concerned about your oil pressure you might want to install a mechanical pressure guage, then you know for sure what your pressure is

 

You may also want to check your oil pressure sending unit. They tend to go bad. A mechanical oil pressure gauge as mentioned earlier would be a good idea if you can find one for an XJ40.

 

Thanks, I will look into the mechanical guages. As for he leak yes i have replaced the valve cover gasket, distributor o-rings, and timing chain tensioner gasket and rings. The leak seems to be in the lower side of the car. Hope it's not the pan

 

I suspect this will turn out to be a flaky pressure sender. My own car went through a period a couple of years ago when the oil gauge would drop down to 1 at hot idle, when it had previously always sat at two kPa on the gauge. Though it quickly rose with engine revs it did concern me enough to have the oil pressure propperly measured by a garage. There was nothing wrong with it; the only fault was the sender unit. Luckily this spontaneously repaired itself when I threatened it with replacement.

Real oil pressure problems on these Jaguar engines are very rare. The sending unit however seems far less robust. In fact early in the life of the X300, Jaguar moved to a simple on off switch for the oil pressure level, which indicates half way on the dial if there is some pressure detected. This is the unit they sell for the XJ40 now, if you buy a replacement. They are a pig to fit though!

 

Just from working on airplanes, when we hook up a mechanical pressure gauge we actually hook up two, so that we can compare the readings between the two guages.

Just a thought. I've seen a bunch of guages that didn't read properly in my time.