One thing not mentioned in this thread is the location of the sender or the switch!

The unit is attached to the block a few inches forward of the oil filter.

The sender is a cylindrical can about 2-1/2" inches long and about 1-1/2" in diameter while the switch type looks like a 3/4" brass nut with an electrical connector attached, very similar in form to the water temp sender on the thermostat housing. Both the sender and switch have a single male "tang" or "blade" type push-on electrical connector. Ground is through the body of the unit to the block.

Larry

 

Oil pressure switch (LNA5642) compared to the OEM Oil pressure sender (DBC5513)

 

Here's a photo that shows the switch-type sender in situ (intake manifold removed):




Cheers,

Don

 

My '91 XJS V12 does the same - oil pressure reading on the gauge gradually drops to zero after about 20 minutes of driving, oil level is good, yada,yada,yada. Does the V12 use the same sender?n How hard is it/how much has to be removed to get to it?

 

I have no idea how accessible it is on the 12, you should ask the guys over on the XJS forum maybe?

However, AFAIK the unit is the same part across the range of cars - Rockauto shows an aftermarket STANDARD MOTOR PRODUCTS unit with a list of alternate part numbers/fitments,

Cheers

Larry

 

There was a service bulletin for the V-12 engine (I think XJ-S) concerning pressure gauge problems, specifically when using 5W-20 synthetic oil but it has been about 10 years since I read it, I think it said what resistor to use to get a center reading. Might be easier to use a rheostat than find the bulletin though.

 

From another source I have been informed the correct resistor value for the V12 engine is 1watt 49K ohm.

BUT - with that in mind, personally I would make up a 49, 75 and a 90 ohm resistor and try each one. The 5.3 XJS engine and the 6.0 litre gauges react differently, so I have read.

Larry

 

I uploaded all these TSBs on this forum. They are here somewhere but Gus has all of them on his site also because I sent them all to him. He has additional ones from others as well.

bob

 

A few months ago I got my Jag back, with new seals and gaskets, all the ones I bought anyhow, but I've noticed with the warm weather, that when coming to a stop after driving for 20+ minutes, the gauge reads 2 bar or lower, and I can smell oil. It is a "new" sender unit that was replaced around a year ago or so, and has a resistor on it, but it reads at 6 bar on cold starts. Not sure if that's normal or not, especially considering I can smell hot oil somewhere..

 

Very interesting thread. I'll have to look into mine, as when I swapped motors, I used the later sender (rockauto showed the same part number for both).

However with the later sender, the VFD oil pressure display sits on 8 bar the whole time it's running, hot or cold. Some time today I'll have to look and see if it's got a sender or a sensor on the block, as I just don't remember.

 

I only use Castrol Syntec oil which might make a difference but in my experience all 6 & 12 cyl Jag engines show rather low oil pressure at idle when at operating temperature except as below.
There is a Jaguar service bulletin concerning low oil pressure at operating temp with synthetic oil. Their "cure" is to replace the sending unit with one that is essentially a switch & resistor so if there is any oil pressure the gauge reads at mid-point.

 

Anyone had any luck with fitting an after market sensor with a sandwich plate?

I have two spare Jap pressure senders and they fit into a sandwich plate, one is 10 ohms and the other 200 ohms?

 

Sandwich plate with pressure sender and oil temp sender.

 

I ordered an aftermarket, (generic rather than Jaguar specific) 10 bar/1/4 NPT transducer today, as my replacement fitted back in 2015 at the beginning of this thread finally gave up the ghost, giving me the oil can dash light syndrome once again.

After re-reading this thread, perhaps I should have ordered an 8 BAR transducer, but at CAD$17 I'm ok to give the 10 BAR a try ...If my math is correct, this unit should read lower than the old one, (even without any resistor) as the range will now be 0-10 bar(0-145 psi) instead of the cabin gauge range of 0-8 bar (116 psi)

No doubt, fitting it will be the usual palaver!

Incidentally, I bought the thing from Walmart online!

https://www.walmart.ca/en/ip/Oil-Pre...d/3WG7HQX131P2

Larry

 

Nice find... Looks like I need the oil pressure sensor as well.

Is it going to be as difficult as it looks to swap this out? Heck, even getting at the oil filter looks like a pain in the backside!

 

I think I always used a metal-band style oil filter wrench with a handle that could pivot to any angle necessary for clearance.



Most of the times I replaced the oil pressure sender or switch, I disconnected the intake manifold, tied it back, and replaced seals and sealant at the various common oil leak points on the left side of the engine. With the manifold tied back, access to the sender/switch is easy. But it is possible to replace the sender/switch from below, or even from above by "feel" if you know the correct wrench size to get the old one off. A crow's-foot wrench is especially handy for loosening the old sender/switch and tightening the new one.

One thing to be aware of is that the sender/switch is a one-wire device, so the ground path for the electrical circuit is through the threads of the sender/switch body to the threads in the engine block port, through the engine block and engine ground strap, through the body monocoque. Any oil contamination of the threads in the block port will add resistance to the circuit and throw off the gauge reading, especially if you have the transducer-style sender. I use a battery cable terminal brush wetted with zero-residue electronic cleaner to clean the threads in the engine block port prior to installing the new sender. It is also well worth the time to disconnect the engine ground strap and clean the corrosion and oily gunk from both ends and from the point at the engine/starter and body where the cable bolts on. Any added resistance at the ground strap connection points can throw off the signals from any of the engine management sensor signals grounded through the strap, such as the coolant temperature gauge, and the ground strap is also the ground path for the spark plugs.

Cheers,

Don

 

The oil filter swap is pretty easy using an oil filter wrench, you can access it from under the car but because the XJ40 is so low, you will have to get the car up nice and high so you can get under easily.
Also, be careful with the oil filler plug in the sump. Just get it nice and snug as it's possible to crack the sump threads if you go all armstrong on it. No power tools!!

Larry

 

The replacement sender I fitted a few weeks ago was the incorrect type. It was a "European" or VDO gauge compatible type, causing the oil pressure on the cabin gauge to rise at idle and drop at cruising speed, opposite way to the OEM/Jaguar or "American" style part.

In OEM transducer / gauge pairings, as pressure increases the resistance drops, but in the VDO style the opposite happens - as pressure increases, so does the resistance. So instead of the gauge reading lower when revs drop, it does the opposite - moves up.

To add to the confusion, both transducers can have similar outward appearance with single connector and same thread.

I removed the "new" unit and fitted a C46272 sender, ÜRO brand. It did read high, as I expected. I’d planned to fit a resistor to get it to match the cabin gauge so I had a 75Ω I’d made up a few years back and also the 60Ω resistor that’s fitted in conjunction with the switch.On the drive home (about 30 mins from the workshop) the gauge showed almost at max and dropped slightly at hot idle as I expected so planned to fit a resistor next day, however about 2 blocks from home the pressure on the gauge dropped down to just above zero.

After parking, I noticed oil stains on the wet road surface that seemed to be coming from my car …so I guessed I hadn’t tightened the sender enough so had a small (well not so small) oil leak.

Today after checking oil level and topping off, headed back to the workshop. Removed the unit again and added teflon tape to the threads, reassembled and started the car. Leak was now worse, dripping oil every second.

Removed it AGAIN and pressure tested it with an airline. It wasn’t leaking at the threads, oil was pouring out of the back of the unit where the connector was mounted on a plastic grommet.

The original sender had been sitting in solvent since I originally changed it the previous week, so I decided to refit it and even if it didn’t work properly at least it wouldn’t spew oil all over the place.

Of course after I refitted it, it worked just like new again. Was probably gummed up.Today I'll be returning the defective unit and do not recommend that particular aftermarket replacement, construction/design not up to the job at all.

Good thing I noticed the dripping oil and didn't go for a long drive - at the rate it was leaking combined with the non-working gauge I could have easily lost all the oil and seized the engine.

The lesson learned? The oil transducers can be cleaned and do not necessarily have to be replaced.

Larry