No Oil Pressure at Low Revs

[SimonR]

Chaps - I'm hoping that disaster hasn't struck!

Took the '40 down to Cornwall (from Cambridge) and half way there, as I slowed down from 70 to 50 for some roadworks, the oil light came on and the gauge dropped from where it normally sits (one stop above middle) to nil. A check of the oil level reveals that it's actually a little over the optimum level (about 2mm above the hatched mark if left over night), not empty as I'd dreaded.

I've ben driving the car all weekend and also just drove it 350 miles home but at anything below about 1,500 revs there's no indicated oil pressure. It's been fun trying to keep the revs from dropping the whole time!

On startup, however, the needle swings rapidly to the normal place but very soon then drops to nothing and only picks straight back up the the normal position over 1,500 revs.

I reckon that it's probably a faulty sender but I guess it may be the pump. Any ideas?

Many thanks!

It's a 4.0L Daimler 6 with 193k on the clock.

[robv12]

the only real way to check is to connect a 'wet line' pressure gauge into the sysyem and check a true reading

gut feeling tells me that the sender on the side of the engine has failed, late 40 and all 300's have a habit of doing this, I well remember the feeling of dread when the same thing happened on my first 300 XJR 10 miles after purchase in the dark, on a Friday at 5.00pm on the M42,

These are easily bought and replace, if a little fiddly, beat got at from underneath, left hand side towards the front half of the engine, it's a brass/silver coloured unit about 40mm in diameter

hope this helps

r

[SimonR]

Rob,

Thanks for the reply - that seems to be the conclusion that others I've spoken to have come to.

Thanks also for your help with the location of the sender - saves me a lot of time searching of it!

I'll replace the part and see what happens. The Duchess is actually about to be decared SORN because the XJ-S is due to be back on the road as of March 1st but I know that she'll be back on the road sometime this summer so I'll let you know how I get on.

Can't wait to be in the XJ-S again - after a 15 month wait it's going to be a very sweet feeling

[nortonjaguar1]

I had exactly the same with my 3.2 Sport. It is common and especially so if you use fully synthetic oil. Provide your Jaguar dealer with your engine number to obtain the correct switch as they were modified internally.

Very easy to get to from underneath the car, use a close fitting spanner so as not to round off the edges of the switch.

Hugh.

[nortonjaguar1]

I had exactly the same with my 3.2 Sport. It is common and especially so if you use fully synthetic oil. Provide your Jaguar dealer with your engine number to obtain the correct switch as they were modified internally.

Very easy to get to from underneath the car, use a close fitting spanner so as not to round off the edges of the switch.

Hugh.

[phirou]

I think an XJ40 with 193k on the clock should run on nothing thinner than 15W-50 (15W50 and 20W-50 are in compliance with the Owner's manual prescriptions). Otherwise, you'll get low pressure under 1500 revs., especially on a hot day.
You might possibly run a low mileage 40 on 10W-40, but even in that case, you might have low pressure at idle.
I'd rather try a 15W-50 first, before doing anything to the car - I am no expert, I tell only from experience.

[SimonR]

I finally got round to replacing the sensor today with a replacement from eBay and it's good news - the oil pressure is back to normal.

In case anyone reads this and wants to know how to do it, you have to remove the following: Air filter box, Air flow meter, air in-take pipe as far as the large rubber bellows bit that is jubille-clipped to the aluminiun throttle body with really long jubilee clips.

You can then reach down under the inlet manifold from above and get a 19mm spannner onto the sensor from the left hand side. It's a bit of a faff because you can only move the sensor about a 6th of a turn and then have to turn the spanner around and go again but it's soon hand-tight and can be unscrewed by hand.

Many thanks to all for your replies - it's nice to extinguish another warning light

[robv12]

excellent, job done then!!