Hi again

On my recently purchased 92 XJS V12 which has 50K Miles only, I am facing issues with the oil pressure.
With a cold engine, at ticking over engine RPM (850), the oil pressure gauge registers full reading, all the way up the gauge.
As the engine warms up towards normal running temp, the oil pressure starts falling down and eventually reads almost zero.
If I engage the gear, the RPM naturally falls down a bit, then even the oil pressure warning light starts to flicker.
If I raise the engine RPM, the oil pressure reading goes up a bit and may reach to the middle reading of the gauge at about 3000 RPM.
I hear no bearing noise at all which makes me feel that no engine bearing issues there. Am I right?
And how can I fix this low reading issue. Oil recently changed as well as filter.

Thanks for any suggestions.

 

What Viscosity Oil did you put in?

Did you have the Same problem Before you changed the Oil?

 

Actually it was worse before as the oil pressure would barely show on the gauge and the mechanic said something was clogged and they cleaned it?!
The oil used is 10-40.

Thanks for commenting.

 

Every XJS V12 I have ever had, had the same problem. It would be best to install a mechanical gauge, see what the real pressure is. I think what happens is that the sending unit sends a bad signal over time, the dash cluster contacts need to be cleaned. I just did my cluster on my 89, and the gauge reads higher now. I plan on installing a small mechanical gauge in the engine compartment, so I can know for sure.
As a side note, I have a 98 Jeep with a 4.0 and 300K on it. It shows 0 oil pressure at idle on the gauge, but the mechanical gauge on the engine shows 10lbs hot. It runs great, doesn't leak or smoke, so I keep using it as a spare.

 

All you can really do is replace the sender and install a different gauge for peace of mind like superchargedtr6 said. The gauge just isn't accurate. If you had 0 psi it would be dead. If the light is coming on I would check your connections and the sending unit though. Mine came on when I got the car because it leaked and since that is where is is measuring pressure and the pressure is lowest due to a leak, the light stayed on.

If you want you can go to the trouble to remove the pan and make sure the pickup screen is clean. These ARE old cars, so POs may not have taken care of them and gummed them up, but based on my experience and the experience of everyone else, the just plain read 0 psi on a hot day and go up when you rev the engine. Nothing wrong with them.

 

If its the Oil Pressure Sender as has been suggested this might help

Sean's Jaguar Tech Pages - Jaguar XJS (V-12 HE) Oil pressure sender and idiot switch location

 

Thank you all for your input.
Actually my mechanic did say that all these Jaguars had this problem, but i did not believe him!
Now you all make me feel much better about this, and I will install a mechanical gauge to double check.
I don't believe it is poor or gummed connections because the readings are very consistent every time. When cold, top reading on the gauge at slow RPM and as the car heats up the reading goes down accordingly. I have taken photos at varying temperatures and did so again, and they are always the same.
At stand still, with no gear engaged, the red light does not flicker, but when I engage gear, it flickers very lightly.
As such, I believe that the sender units are not accurately manufactured or loose their tension to read accurately, thus the poor reading.
Alternatively, it may also be a charachter of these engines that they do not have much pressure at slow RPM??
My 190 SL even when engine is warm, has about 50 lbs of pressure at about 650 RPM.
My 450 reads at full gauge (has 1-3 on it).
My 70 Aston Martin reads 45 lbs also when hot at slow RPM
These are the only cars I have that have a graduated oil pressure gauge, thus what I can relate to.
Is it possible that the oil pressure pump is worn out??
Anyway, I will find out more when I fix a mechanical gauge to the system.

Cheers
Farouk

 

The only V12 I ever had that had exceptional oil pressure was my 71 E Type. Easy 45lbs hot and idling. I think it was a anomoly. What I have found out however, that a new Honda engine may only have about 9lbs of oil pressure at idle when brand new. Oil pressure robs power. The japanese manufacturers figured this out long before we did. Even if we only have 10 lbs of oil pressure at idle, this is plenty to lubricate the engine. I feel that it most likely is a combination of several factors, most likely being the effect of heat on the sending unit being buried where it is.

 

Is anyone else here running 10w-40 in their V-12? I run Castrol 20w/50. Pressure always reads zero at idle on mine after its warmed up, nothing unusual.

 

Just FWIW

My V12 always had low O/P at idle when hot, even with20/50. The gauge needle would 'just' touch the zero line.

Drove it like that for years.


Cheers
DD