Oil Warning Light 89 V12.

[Flappers]

Hi, not posted for a while, things have been fine on the car for most of the summer, new injector & EAV fixed all my issues. Thanks Bob if your reading this

I was driving back from taking my girls out and we stopped for treats. As i started the car again I noticed that the oil warning light stayed on. I panicked thinking it had let go on a seal so I stopped, checked for big puddles of oil and nothing. I drove very gently home, got the lead lamp out and checked the oil. Oil was at a mid level on the marked part of the stick, I topped it up to just below full and started her up again and the warning lamp stayed on. I havent tried today but had done probebly 15 miles round town so the engine was at running temp for over an hour. The oil presure gauge is still showing the same as allways. It drops to low at idle and improves when the engine revs, I have flagged it up before but was told not to worry about it so i diddnt. Had a few series 3's and the oil presure gauge has never been reliable on any of them from memory.

Can anyone suggest what to do next please ?

( Daimler Double Six - 1989 - 102000 Miles )

[davidr]

Sam - this is more likely to be a failure of a pressure sensor than anything more serious. The sender for the instrument pack is entirely separate from that for the low pressure warning lamp.
If you're showing pressure in the instrument pack then that's what should give you comfort. It will drop quite a bit at idle and rise as the revs do. I can't remember what the high and low pressures are (despite having a 1989 V12 myself!) but there is a fair difference.
I would be investigating the low pressure switch which is on the oil feed pipe at the back of the cylinder heads.
Hope that helps
David

[Flappers]

This is what the oil pressure is this morning after 3 min of running on a cold morning. No warning light and a healthy number on the gauge? Is the sender for the light at the bulk head side of the engine please.?

[davidr]

Hi Sam - that looks a healthy oil pressure. How many revs to get that pressure?
The sender for the pressure gauge is in the vee behind the throttle pedestal and the sender fir the light is on the oil rail behind it that goes between the 2 heads.
Regards
David

[Flappers]

Thats on a cold start at about 13/1400 RPM. I left it running in the garage and when I checked again when warmed up it was at just a smidge under 40 at 2100 RPM and at idle - 900 RPM - I'd say 15 at a guess. I'll link images.

[mike020150]

As has been said, the oil pressure gauges on these cars are not noted for their accuracy or reliability. Added to those issues are the vagaries of how you take the readings. It takes at least 20 miles for a V12 to thoroughly warm the engine oil. Therefore, any pressure readings after lower mileages will be higher than the 'true' readings you need to judge if there really is a problem. When thoroughly hot, a V12 should show between 60psi and 70psi on the gauge at 3000 revs depending upon wear and tear and the grade of engine oil used.
Many modern oil filters (including Jaguar badged ones) do not have sufficient oil flow capacity for the V12 at high revs and potentially can cause problems. Although physically smaller, the modern 4.0 litre V8 filter (EAZ 1354) has a higher capacity well suited to the V12.
Badly leaking fuel injectors can dilute engine oil reducing its viscosity and pressures, the same effect as very old and dirty engine oil.
Additionally, the V12 has an oil pressure relief valve (luckily, external to the engine) which can jam partially open, causing lower oil pressures.
So, there are several relatively easy to solve issues which could have a bearing on low oil pressure readings. The best thing to do is to test the car (thoroughly hot) with a good old fashioned wet oil pressure gauge of known accuracy. Any good garage should have a decent gauge and be able to test the car's oil pressure at a modest cost or buy one yourself. Then, armed with the results, a better diagnosis can be attempted. Mike.

[Flappers]

Much appreciated, many thanks