Hello
I have a problem with my XJS V12 engine oui pressure.
After the motor dismantling, the cylinder heads complete refurbish, distribution change, motor deep cleaning, oil hoses renewing and cooler plus oil circuit cleaning, oil filter changing I reassemble the engine and put the engine back to the car.
After many tests and couple of hours of operation I still have a problem. When starting cold the oil pressure is correct, but it goes down slowly with the temperature increase. When temperatures is normal, the oil pressure gauge is about half way between 0 and 50. The low oil pressure switch and warning light never went out.
I didn’t touch the oil relief valve setting when dismantling. I put the oil quality (viscosity) recommended by Jaguar original table.
Does anybody has an idea of the possible origin of this trouble and the solution, please?
Thanks in advance for any advice.

 

The V12 runs at very low pressures compared to some cars and that confuses some owners When warm, pressure at idle is just 7psi. If your gauge is reading 25psi at warm idle, everything is fine. Maybe your light is just rather sensitive?

Try connecting a mechanical gauge and compare that pressure to your gauge pressure.

Cheers

Paul

 

As Paul wrote, the oil pressure is fine, 100% normal, on the guage. No worries about that.
If you are saying that the oil pressure warning light is always on, then I would first replace the warning light sensor on the small oil distribution tower at the rear of the V. BUT be VERY careful to support the tower against the torque of undoing the sensor, as it can easily snap off, otherwise.

 

Adding to the above:

I suggest unplugging the Oil Light Switch. The light should go out. If it does, the switch is the problem, as said.

The Oil Light Switch is NOT unique to Jaguar. I use a Toyota spec switch (old corolla from memory), same thread, same spade terminal, the engine is happy, and the light is out.

If the light stays ON when unplugged, that wire is earthed somewhere, and that is quite common now. Easily fixed.

 

Hello
i see there is a misunderstanding- the Light warning is NOT on, thus the it is not a problem of the SWITCH it is a problem of the analog measurement or maybe really the pressure control problem. As the pressure is normal when oil is cold and go down when hot I first thought it is oil viscosity issue, but I used the standard recommended one….
Maybe I will replace the oil pressure sensor (not the switch) to see if there is any difference.
The engine was dirty if the oil sediments inside - especially on the top gallery when I removed the top middle cover between the heads and under the distributor.
All outside oil circuit was removed and either cleaned or simply replaced by new. Also in the area of the timing chain there was a bit accumulation of the oil dirt. I also took of, clean and reinstall the oil sum with new seals etc.
can this
Is there any setting to be done or changed (oil relief valve for example)?



QUOTE=Grant Francis;2617280]Adding to the above:

I suggest unplugging the Oil Light Switch. The light should go out. If it does, the switch is the problem, as said.

The Oil Light Switch is NOT unique to Jaguar. I use a Toyota spec switch (old corolla from memory), same thread, same spade terminal, the engine is happy, and the light is out.

If the light stays ON when unplugged, that wire is earthed somewhere, and that is quite common now. Easily fixed.[/QUOTE]

 

MAAAAAATE.

Your oil pressure is fine, maybe better than fine.

ALL mine have had that kind of reading, and the one now at over 700000kms, is still the same. That engine is untouched since 1976.

Worry NOT, the dash instruments are ONLY a GUIDE, and have NEVER been promoted as anything else.

Time for a beer, its 42C here at 7PM, Bugga.

 

Grant 100% correct, as always. My car runs at about 25psi on the guage when the oil is hot at about 20o0 RPM. Leave well alone!
It may interest you yo know that Jaguar got so tired of people fretting about the V12 oil pressure that they changed to sensor so that it ALWAYS read 50 psi unless the pressure dropped below 10 psi !

 

It's also perfectly expected for the pressure to read (sometimes much) higher when cold. As it's settling back to 25psi on the gauge when warm, I'd suggest all is fine.

Paul

 

Oil gets forced through small jets and galleries inside the engine, and when oil is cold its thicker thus creating more resistance to flowing through. You get high pressure when cold. Once the oil is warm and runny it goes through the passages more easily and the resistance to flow decreases and the pressure will settle in what you would call its normal reading. If over time that normal reading drops and drops you've got wear and clearances increasing. Engine oil is like honey when cold, and almost like water when hot.