Jaguar XKR 1999 (4.0).
After driving for a while, the oil pressure drops at idle, if the car is engaged in "D" - drive. If I shift to "N" - Neutral, the oil pressure goes back to normal. The oil pressure is also going back to normal if I just exactly press the throttle.
It does not happen right away when starting. Only after driving for a while. I don't expect it to have anything to do with the gearbox. It is just because of the idle rpm when the gearbox is engaged. Idling around 600.
I took the pan off and the oil pick up. Absolutely nothing. Not a single piece of plastic to block the pick up. Nothing in the pipe, nothing in the pick up filter.
Fresh oil (synthetic 5W30) and fresh oil filter.
Mileage 70000 km (43500 miles) from new.

Any ideas? Sensor? Oil pump?

TIA

Bo

 

What is the air temperature where you are driving the car ? For my climate with summers well over 110-115 (42-46 C) z F the driver handbook recommends 0w-40 or 5w-40. A heavier oil than your 5w-30 might raise the pressure slightly.


But first I would be checking the pressure with an accurate mechanical gauge. Then you would know for sure if the pressure is OK or not. If it appears OK, then the sending unit replacement does sound like the logical next step.

without an audible knocking noise, I’m inclined to say the bearing clearances are not the issue.


Z

 

It's normal to have the pressure drop at idle. If the red waning light doesn't come on stop worrying.

 

Did you install a 'REAL GAUGE'? https://www.thejagwrangler.com/xk8--...realgauge.html
The oil pressure switch is a SWITCH and the gauge reads mid scale. (it is not a real variable gauge)
Try a NEW oil pressure switch?

 

It is still the factory switch. Not a real gauge.
Maybe a slightly thicker oil will do the trick?

 

hooking up a mechanical oil pressure gauge before changing the oil, or replacing the oil pressure sending unit, will definitively inform you whether the oil pressure is actually low, whereas there could be one of several causes.

Conversely, if the mechanical pressure gauge shows the oil pressure to be normal, that would indicate that the sending unit is at fault.

Always best to get the most information possible before changing part(s), even oil.


Diagnostic Theory and Strategy:

Much time and money can be saved by following a specific investigative procedure when troubleshooting any issue. A successful technician, in the transportation field or otherwise, will always follow a well established diagnostic list, in the specific order of what would be most likely fault, based on collective experience. That will always save the tech the most time in the long run.

In your case, knowing if the sending unit is passing along reliable and accurate information is the first step. .

Z

 

Its not clear how you know the oil pressure has dropped ....Did the warning light come on? did it flicker or do you have real gauge,
The pressure switch that works the light turns it off at 0.45 BAR approx 7 Lb /sq in.
You need a mechanical gauge those electric ones are crap.

 

The OP’s post #5 quoted above mentions briefly that its “not a real gauge”. Inferring that he’s relying on the stock oil pressure sender & light .

I’m with you. Hook up a mechanical gauge and check the pressure at various rpm’s and with the engine fully warmed up .

Z

 

First job change the oil pressure switch ..Cheap $ 10 . Its only a spring operated switch and the springs can go weak with age etc
I have one on my desk now to put in before my next trip to france

 

A cheap obd reader ($25 off Amazon or E bay) and a phone app like Dash Commander can give you an actual oil pressure reading on your phone

 

Oil pressure cannot be read via OBD since there is no analog oil pressure sender in these cars.

 

hence the advice given in several posts to purchase a mechanical oil pressure “kit “ which will have several threaded adaptors, one of which will fit into the same place where the current sending unit is fitted. It will take all of 10 minutes to fit the gauge and bring the car up to operating temperature and then observe the gauge reading.


Z