Several days ago, I started the car in the garage and noticed a low oil pressure message together with a zero indication on the oil pressure gauge. The low oil message wasn't there the last time I started the engine which was a almost a week prior. Now, for some unknown reason, I succumbed to an inclination to rev the car engine up a bit. In any case, the warning and gauge didn't change, so I killed the engine immediately and left the car in the garage. Hoping it was a sender or wiring problem, I ordered a new sender to have it ready for further investigation during a warmer bout of weather. Well, the sender arrived and I thought that before I got under the car I would see if the low oil pressure message was still there. So, today I started the engine again. This time, there was no low oil pressure message and I saw the oil pressure needle start to move up towards the center of the dial. However, just then the idle became rough and the engine stalled. I tried again and the engine turned over roughly for a few seconds, but then just turned freely without starting.

I'm thinking bore wash from the previous low oil pressure start, rev and engine kill. So, I'm about to go out and remove plugs to put some oil in the cylinders.

In explaining to my wife what was going on, she asked why this has never happened to any of the other cars we've had.

Which is a good question. What makes this engine so susceptible to bore wash??

And why did I get a low oil pressure message almost a week ago, but I got (apparently) oil pressure today?

 

Many questions, the answer being it's a Jaguar. In a case of bore wash the engine usually doesn't start at all. It usually occurs on nikasil lined engines which don't hold oil as well as iron or steel.

Shutting down after starting and running rough makes me suspect the fuel pump. After tuning the ignition on check for fuel pressure by pressing the schraeder valve stem on the fuel rail. There should be 40 psi so a good spurt should be observed.

The oil pressure issue may be a failing sensor or bad connection.

 

It's a weakness of the early V8's. You may have noticed when starting the engine from cold that tickover is at higher rpm than normal.

Immediately after firing, the engine management system sets rich fuel and high rpm to accelerate the warm up period. The logic behind this is it causes less wear.

The cooling system is "low volume/high circulation rate" and it only takes a few minutes for the temperature to rise to the point (determined by the ECT sensor) where mixture and tickover rpm are then returned to normal.

If you switch off too soon, whilst the rich mixture/higher rpm is operating, the the next start will be with the rich setting. Too much fuel can flood cold plugs preventing spark and can also wash the thin film of oil from the cylinder bores.

The recommended method to get round this is to attempt starting with the throttle prressed fully to the floor. This temporarily stops the pump from delivering more fuel.

Graham

 

The throttle to the floor worked this morning. It started right up and the oil pressure was OK again and stayed OK for a 4 mile drive.

However tonight on starting, the oil pressure went up (and seemed a little slow doing it) for only a couple of seconds and then went down to zero with the warning message appearing. But a quick blip on the throttle and back up it went and stayed there. So, a failing sensor maybe as RJ237 suggested?

Someone asked this in a past thread but got no answer: - do you have to drain the oil to change the sender? Or, if yes, any guesses on how much oil would drain out of the sender hole (with the car jacked up on that side)? Or, again, with the oil cap on, would the oil drain slowly enough to allow a quick swap of senders with just a little oil lost?

 

Good to hear you got the vehicle started and running again.

The oil pressure sender is screwed into the side of the filter mounting. Here is the illustration from the Parts Catalogue showing the sender and washer top left with the location arrowed in red:



Not necessary to drain the oil to replace it although you should take the precaution of first waiting for the engine to cool.

Another cause of slow pressure build up and erratic pressure can be the wrong oil filter. Are you using an OE Jaguar filter (which has a non-return valve) or an aftermarket filter with a non-return valve?

Graham

 

Had oil changed fairly recently by local Indie and not sure which filter he used. Will wait until we have another spate of milder weather to change the sender - and maybe the filter as well.