I got a different 1993 XJ40 a couple of days ago and gave my girlfriend my red one. I drove this today in an interminable line with about an hour of idling. It heated up slightly but would go back to the middle very easily. But whenever I was at an idle the oil pressure would fall into the red and the light would come on.
I asked my parts guy what he thought and he said that he never sells oil pumps for these cars but the sending unit can leak and cause that.
Itīs at the repair shop now. They said the sending unit is dry and not leaking. Right now they are changing the oil with the 20w50 castrol that I bought for the car. The car was not low on oil. I donīt know what viscosity was in the car.
Any ideas? I hope I donīt have a disaster on my hand. The engine runs perfectly. No smoke, noise, etc.
I saw another thread about the oil pressure light on X300s and Doug indicated that they can have a bad sensor. Is there a separate sensor on the XJ40 and where would it be? Could I just be getting an inaccurate reading on the gauge?

I guess I should have kept my 1993 and picke up that V12 XJS I was thinking about.
Panza
2002 S type 4.0
1993 XJ40
1993 XJ40 Sovereign (with girlfriend)
1992 XJ40 Sovereign
1985 XJ6
2004 Lincoln LS

 

No dash gauge on this one also?

The sender can syill be bad.
The idiot light sender is just a switch.
It is "calibrated" to a spring.

Hopefully, your shop screwed a mechanical gauge in the hole and ran it to SEE what the pressure is.

I keep a couple of them around with various adaptor fittings just for this purpose.

20/50 is what you should be using.
My MK2 came with 20/40, sticker still on fill cap so stating, and at 95K, I went to 20/50 Kendall last change.
World of difference.
Holds 20 hot idle, 50 on the Interstate.

 

This has a dash gauge and an idiot light. When the gauge goes to the bottom of the red, almost at zero the light comes on the dash.
They put in the 20w50 and have been running it for a half hour. At this point he feels that there is a problem with the gauge. With the brake lights on the pressure drops. When the fan comes on the pressure drops. In other words with an increase in voltage the gauge goes down. In park with the brake lights off the pressure increases. Sounds like a bad gauge if not the switch. Tomorrow AM heīs going to messure the oil pressure with his own gauge and weīll know for sure. He wants to do that with the engine cold.
Meanwhile for some reason the trunk wont open for him no matter what he does.
It opened for me this AM when I tried to see why my antenna stopped going up and there was zero AM radio and barely any FM.
Iīm already opening negotiations with my girlfriend to get my red Sovereign back.
Thanks for the feedback. If you have any more thoughts please let me know. I asked the mechanic if there was a sensor as well as the pressure switch and he says that he does not see that and there is just one wire from the pressure switch to the gauge.

 

Oh, one of THEM gauges!
The red light senses off the gauge.

Could be the gauge.
Could be the instrument regulator if it has one of those (but fuel and temp would be way off too).

Fan coming on loads the alternator, could lower RPM's enough to trigger it.
Brakes, if vacuum boosted, could do the same.

Tell me what cold oil pressure is.

Hopefully, he will leave the gauge on and run until hot and see what it reads then.

 

I have to wait until Monday because the mechanic needs an adaptor to make his oil pressure gauge fit the jaguar.
I started the car and the gauge went right to 4 (40?) on the oil pressure reading.
The problem seems to be only when the motor is hot (thinner oil) and when in drive and the brakes on. (lowest revs)
I was told by another Jaguar owner that the gauges are actually run by a computer and there is a transducer, rather than the pressure switch telling the gauge what the pressure is. I have no idea.
The car had sat for a long time and now thereīs all sorts of weird electrical problems. The trunk will not unlock no matter what. With the remote, with the inside release button, with the doors unlocked, with the key etc.
The radio antenna stopped going up and down and I opened the trunk yesterday to see if I could get a look at it and no problem then.
I was told that if these cars sit a long time it may be necessary to pull the fuses and relays and reseat them. The relays possibly may need to be lubricated with wd40.
Anyway if the gauge was reading correctly with the motor cold, maybe there really is a flow problem at high temperatures and low engine speed. I donīt know what would cause that if the oil pump is working properly. Donīt know if the low mileage car has a lot of wear on the motor. Perhaps I could do a quick remedy by having the idle raised.
Iīm getting a bit upset by this. I have to use the car to cross the border and it requires one to two hours of creeping along and idling. I canīt do it if the oil pressure will go to zero and certainly canīt do it if I canīt open the trunk for the customs inspectors. At this point I donīt have the slightest idea how to get the trunk open. Iīve tried everything that I can think of. When I open everything with the remote I hear the solenoid click in the trunk, but the black button is stuck shut and you canīt even open it with the key. Weird stuff.
I may have to take back the red XJ40 from my girlfriend. She only drives locally and the car wouldnīt have to tolerate one to two hours of idling.
I donīt know what to do at this point.

 

Could be.
With the newer computerized stuff, I have no doubt they went to something more complex and less easy to fix with the oil pressure going through the confuser.
Maybe the confuser is not allowing the boot to open because the oil pressure is low.
(Joke, son, just a joke).

You hear the solenoid clicking in the boot latch?
Tried bouncing the lid whilst someone is busy cycling the release?

 

Thanks for the feedback. There is another possibility. That the gauge is correct and there is a slight blockage in the flow of oil. The car sat for a long time and just got fresh oil today. Maybe something is gumming up the works slightly and it only causes the pressure drop at the lowest rpms.
Perhaps the new oil and some usage will clear this up.
Monday the mechanic will measure the oil flow. Heīs thinking of calling a locksmith for the trunk. Another mystery. Weīve pretty much tried everything at this point.
Meanwhile my girlfriend returned the red xj40 and Iīm happy to get it back. She doesnīt need two cars. But then again I donīt need six. If one is always in the shop it solves the parking problem. Maybe Iīll give her this new one when itīs done. But the interior and body is nearly perfect and only 69K miles. So what if it will blow up when I idle it and I canīt open the trunk?

 

Seriously doubt oil flow.
Not at the gauge sender.

 

I hope youīre right, buddy. I should know tomorrow and Iīll post the results. Thanks for the help

 

dmarcos, I started another thread about this problem entitled I think I was screwed. This is because I just drove the car one day when I found this problem.
It turned out that the oil pressure sending unit and the gauge are reading correctly. With the engine hot and at very low rpms the oil pressure is insufficient.
The mechanic also found water in the oil. Heīs going to see if by putting in an oil additive the oil pressure will improve. In that case we believe that a head gasket repair will fix the problem. I am assuming this is the case because if the oil had water in it that could cause low oil pressure when the oil is thinnest and at the lowest pressure (hot temperatures with low revs).
If the oil pressure doesnīt improve weīre going to have to dig deeper and see if there is any low end bearing damage to the motor before we proceed. However, Iīve been told by my Jaguar parts guy that he believes this is unlikely since heīs never sold an oil pump and these motors are pretty strong. He very rarely sees lower end engine problems.

 

these cars have a low volume oil pump and only pump what they need. It is very important to have the correct oil and make sure it is changed regularly. Oil will break down over time whether it is used or not. The oil pump will have a hard time pumping thined out oil. Did the oil change make the light go away?