THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

Yes ~ these unrelated things happen but I still think it's good counsel.

It's all well and good saying that Glyn but in the past I have had a fully running functioning engine then I have changed a rear bulb and the engine no longer starts. Sat for ages scratching my head wondering what the hell I could have done at the back of the car to stop the engine from starting.

Turns out nothing and I was just unlucky that at the time I was changing the bulb for no connected reason my coil gave out.

Took me ages to sort that one out.

Rob ~ as you well know ~ always interrogate what you touched last.

Could be as Glyn has stated either gauge or sender unit playing up as you have not done anything to the engine itself.
I have a similar same problem in that my oil pressure gauge stopped working. Got under the car to check that the terminal was still connected to the sender and found the wire had wrapped itself around my steering arm and had snapped. I repaired the wire and re routed it so it would not happen again but now my oil pressure barely gets above 20 psi on the gauge where as it was running at 40psi.
I am not too concerned as I have not touched the engine so the problem must be with the electrics. I now plan on changing the sender unit and I have a spare oil gauge which I am cleaning and then I will fit both to see if anything changes.
I might even send one of the gauges away to Speedy Cables to have it calibrated correctly. Details of Speedy Cables at https://www.speedycables.com/instruments/ I have used them before with the gauges in my Lotus Seven so know they are good.

Have you disturbed any wiring?

Your oil pressure should be between 35 & 45psi at 3000RPM hot dependent on oil viscosity ~ most run at approx 40psi max on an SAE 30 (remember an SAE 10W-30, as an example, is a 30 at operating temperature). Sender units on top of the oil filter housing are notoriously unreliable. Gauge might be suspect.

Have you done an oil change recently?

At the numbers you quote your pressure has been reflecting nonsense for a while. No XK engine runs at 60 psi. It's not an Aston Martin that runs at 100psi. This due to aluminium Block with dry liners & steel crank ~ variable expansion rates of materials used.

The XK engine needs flow ~ not high oil pressure.

After fixing my electrical issue (new dizzy cap & rotor) and going for a test run, I noticed to my alarm that my normal good oil pressure (50-60psi running, 20psi at idle) all of a sudden is all over the show and nowhere near the previous figures.
Any ideas please ?