97 XK8
92,000 miles
Cold start normal. At full operating temperature and idling, pressure gauge moves to zero and "low oil pressure" warning lights. Rev engine above 1000 rpm and everything returns to normal. What gives?

 

Well here's a secret. That and the temp gauge are idiot gauges. They always stop at midway, but they don't give out any information after that unless the engine is seconds from committing seppuku, at which point, shut it off.

 

Right. But the car is still running! Should I rather suspect a sensor issue? Apart from testing the oil pump itself for outputs, is it common for the pump to fail only at low rpms?

 

Mine exhibited somewhat similar symptoms after I installed Steve's Realguage. Turns out I cracked the OEM oil pressure switch during installation. Replaced it for under $20, problem solved.

 

+1 to comments on the gauges.

I'd suspect the sender/sender harness connection before the pump.

Graham

 

Going to try something desperate: change the oil. It's been 6000 miles since the last oil change and much idling-- possibly leading to viscosity breakdown. If that fails, step two will be the switch/sender change.

 

In a slightly relatable hijack, if we were to pull the oil pump, is there any reasonable way to bench-test it? Just curious, since it's sooooo pricey.

 

from what I gather, pricey and difficult and expensive to access. I was going to mention beyond my means but first I'm going to change the oil.

 

Went to the local Jaguar Dealer this morning after calling yesterday and explaining the problem. They said "sign here" and pay us $125 to diagnose the problem, and if it's the sender switch, we don't have that in stock, but if we did it wouldl cost $136 plus labor to install." I walked out. The way these guys operate to find out what's wrong is wrong. There should be no diagnostic charge. And they wonder why their shops are a bit empty. Sure, there is a step by step logical approach but skip a step every once in while, or lose business.

 

The oil pump is behind the chest plate running off the crank, if you were doing your tensioners you could remove it...... But to be honest they are pretty bullet proof I have never had one go...... However done plenty of senders!

 

Changed the oil and the sender but still have problems.

 

Could it be the bearings?

or could it be debris?

Next step? They changed the oil to 15/40 per my request. Slightly less likely to show low oil pressure. Should I go to a higher viscosity and or Lucas Oil Stabilizer?

This car is basically running perfect other than the low oil pressure warnings.

 

Until you are sure exactly what is going on pressure wise it's guesswork. Back in the day we had a Smiths Industries mechanical gauge test kit with a selection of adapters to check oil pressure at the sender outlet. If you can get hold of a known good gauge and connect at the sender point you will know exactly what the pressure is and that would help. Low oil pressure at idle speeds is a classic symptom of worn bearings but could also be debris( from tensioners???) blocking the oil pump pick up screen. I think I also remember a post on here sometime ago where the oil pump pick up pipe had worked loose. If it was my car and I couldn't get hold of a test gauge I would drop the sump and have a looksee.

 

5 psi at idle.

 

Tensioner crack bleeding oil pressure but not killing the car ... Yet?

 

Next step would be to drop the pan and examine the pickup and sump filter. If they are clean about all you can do next is check crank bearing clearances.




Dave

 

If I baby her, how long does she have if its a cracked Tensioner?

 

The tensioner crack could lose it (oil pressure).

 

Next minute/next hour/next day/week - no way of predicting. Sort of Russian roulette with a very expensive engine.

 

I may have one. I have low pressure. It probably isn't bearings yet.