Just installed a 99 AJ27 engine from another XK8. The process went fairly smoothly. Had an issue with the fuel rail so I took the one off the engine that was removed. Started the engine and runs smoothly. Oil pressure came up immediately, or the usual delay after changing the oil.
Took it out for a test drive and found no issues.
Gave the car to my daughter to drive. Two days later she informed me than the oil pressue would drop while stopped at a traffic light with the car in drive.
This engine had been sitting for about 5 years and thought I should check the oil pickup for any blockage. Dropped the pan and the pickup was caked with old oil that looked like it had dried or deposited on the screen. I cleaned the pickup and reinstalled it with the oil pan. Installed new filter and added new oil. Restarted engine. The oil gauge on the dash came to the normal position. Put the car in drive and the gauge will fluctuate between normal and low. What I unserstand is that the gauge will show low if less than 5 lbs and normal if above 5 lbs.

I'm thinking I have a bad oil pump. Thinking that its sitting so long and the stress from trying to suck oil through the restricted oil pickup may have damaged it.

Plan on changing the pump this weekend.

 

Let's hope the new oil pump indeed resolves your issue. Keep us posted....

 

Have you considered a possibly bad low oil pressure sensor?

 

Bob, I installed the Real Gauge for the oil and that was a concern on the oil pressure drop at idle.
After talking to a few, this is normal, well, I was raised on cars that if they showed under 15 PSI at idle there was a problem.
Still don't like it, but with out a red light going to try and get over it.
Thanks for the heads up on the oil screen, I may do that just to make sure.
I'm surprised you are getting a reading if you don't have the Real Gauge, as mine just stayed in the middle after running.

 

I ruled that out. If it was the sensor why would it show low oil pressure while idled in drive. If it was bad I think it would show low pressure under varying conditions. I also took the oil filler cap off while car was idling. I noticed less oil when it was put in drive compared to park.

 

I read in a post somewhere in the forum that under 5lbs is where the gauge drops and the red light comes on. I think mine must be on the edge of where it is a little under, causing the gauge to drop and the light to come on , to just over 5lbs. I think that is what is causing the gauge to jump back and forth.
Not an expert, I'm just guessing.

 

Bob, thanks and yes you are right to have concern.
Like others, hope a new pump will solve the problem.

 

Hi Guys,
My Light was coming on at idle.....Stop Lights and such......Replaced the sending unit...all is now OK!

Billy Clyde @ Cinco Ranch

 

I forgot to post the solution. Turned out to be the oil pressure sensor. No more problems since changing the sensor.