I have thoroughly abused 97,000 mile 1998 XK8 convertible (AJ26 motor) that has over 50psi of oil pressure on a cold start and around 30psi warm on a warm start, but it gradually dies to near zero as it reaches operating temperature, and no amount of engine speed makes it recover.

Has anyone else experienced this, and knows what it could be a symptom of?

It came as a non-runner full of clean new oil after a "top end rebuild" - I've since got it running, but don't know what oil is in it. Could the wrong oil type be causing it, or is it more serious (oil pickup or pump)?

TIA,

 

Where are you getting your oil pressure readings from?

 

Oil pressure test kit from Hobo Freight: https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html

 

If the top end rebuild didn't include the primary tensioners and guides, it's possible that the primary slipper guides could be shedding plastic.

If the sump wasn't removed and cleaned out, the detritus can find it's way into the oil pump pickup strainer and restrict flow.

Appreciate that's a few ifs, but it has been reported before.