Hi,
I have a question/concern about my xjs. When I start the car the oil pressure is about 58 psi which I think is great. It stay at 58 for a while. Then after the car has been driving for a while (30+ min) the oil pressure oscillates between 58psi and 40psi. Never in between, just one or the other.
Any idea why this is happening?

 

My 94 six cylinder oil pressure was vibrating. I put on a new sending unit. Solved.

 

My oil pressure gauge misbehaves too, but in my case it just starts out at 50psi and then after a half hour drops to about 10psi. Under load, it rises a bit, but otherwise it just reads low and makes me nervous.

 

Jomo,

First of all, I would establish if you have the earlier or replacement type of 4 litre oil sender unit. As you probably know, Jaguar had to bring out a replacement sender unit to pacify American owners who complained that their oil pressure gauge fluctuated at different revs and temperatures (which it should do!). The replacement type has the same part number but it acts almost as a on/off switch in order to hold the gauge at the mid-position, irrespective of the actual oil pressure. The pressure has to be very low before the gauge will drop.

I would suggest that you first measure the resistance output reading of the sender gauge to see if it's giving true variable readings or the "fixed" resistance reading. Then you'll work out which type of sender that you have and also possibly diagnose if the sender is at fault.

Good luck

Paul

 

I changed mine every year because the after market ones were rubbish.
The vast majority of modern cars do not have an oil pressure gauge so nobody frets about it; you are supposed to rely on the low pressure warning light.
If the warning light stays off then you should be fine.
As long as you are completely, absolutely and firmly convinced that the bulb is still working of course.
Which you can't test whilst you are driving along.