My XJ40 had sat for 10 years. 80k miles. Oil pressure was quite low, 20-25% of max reading.

Put Seafoam additive in the oil in the quantity specified on the can. Run car for ~20 minutes you can idle it at 1000-1500rpm. Be VERY careful that your oil pressure does not drop catastrophically or that the engine temperature is not excessive.

Next change the oil and filter. The oil sump nut is 1-1/4"; very big. Use synthetic Mobile 1 0W40. To get to the filter, remove the left front wheel (US Driver's side) and jack the car up. It is then easy to get an oil filter wrench in there. My oil came out as thin milkshake.

Your oil pressure should radically improve but check the oil every 30-40 miles as there may be more crud loosening up inside the engine after the oil change. When/if your oil pressure acts out again, replace at the very least your oil filter and probably also the oil. You should now be in good shape.

Next, run Seafoam product in the gasoline to clean the injectors.

 

Hi High123bid!

I don't know if you have an owners manual for your XJ40, but if I recall correctly, Jaguar specifies 20W-50 oil for the XJ40 in most climates, and 10W-40 in cold climates. The specified oils are conventional, not synthetic. In my experience, using oil of lower viscosity or synthetic oil will contribute to low pressure indicated on the instrument cluster gauge and may also promote increased timing chain rattle at start up as well as increased oil leakage.

The AJ6 is not known for low oil pressure problems, but it is known for problems with the oil pressure sender/transducer/switch. It's a single wire unit whose ground path is through the block. Oil contamination of the sender threads and/or electrical connector (spade terminal) add resistance to the electrical circuit and cause false low pressure readings on the gauge.

False low readings may also be caused by sludge formation on the tip of the sender, which your cleaning procedure may have dislodged.

In any event, I would not recommend 0W-40 oil, or synthetic oil, in an AJ6, even in Minnesota, and certainly not in Arizona, since the engine was designed for oils of higher viscosity.

My two cents.

Cheers,

Don

 

100% with Don on this. Synthetics with their smaller molecules will also form leaks where no leaks were before ...stock up on GTX 20W-50 on sale!

Larry

 

There are pros and cons. Personally, I already had an upper chain tensioner leak and a crank inspection leak. I described in a past post how to fix those. It was very simple. Cost about $40 in O-rings and gaskets/gasket in a tube. No other leaks have developed. Regards, Bo

 

If possible, always use products recommended for the designed technology.

Oh and BTW, never had to remove front wheel to remove/replace oil filter. It is quite accessible, at least on my car. I use WIX filters with Castrol GTX 20W-50.

The oil pressure sender low reading problem is well known issue, several threads about this in the archive incl. recommended aftermarket replacements and resistor values etc.

Larry

 

Greetings, fellow sufferers of Jaguar dementia! Regarding oil pressure indicator problems, I'll share my experience of today. My late-'94 XJ6 just came out of hibernation yesterday. It always had a flaky reading on the gauge, but no idiot light. Yesterday was the exception. I noticed no indication whatever after firing her up for first time since last fall. Removed the filler cap, sure enough, oil flinging all around in there. Took the chance on driving the 6 miles from storage to home, parked it. After poking around on this site & researching the subject a bit, I commenced to finding that pressure switch. In the connection from wiring harness to switch I found a pig-tailed-in resistor which indicated 150 ohm, 1/2 watt, 5% tolerance based on the color code (brn/grn/brn/gold). Upon checking this with a DMM, it indicated a bit over 700 ohms, a considerable difference. I dissected said assembly, replacing that resistor from my junk bin collection of resistors & such via soldering-in & shrink-wrapping. Meanwhile, I tested dash indicators by shorting the sensor wire to ground, all systems go, gauge pegged as I believe it should. Reinstalled the renovated pigtail, problem apparently solved. Now, I wonder about the accuracy of the oil pressure gauge which may never have been accurate to begin with. Would it benefit to remove the resistor altogether from the circuit? Researching it via schematic of wiring diagrams shows the feed wire going to an ECU of some sort. Any knowlegeable input appreciated, and as I start revisiting a few issues with the car, I'll likely become a nuisance on these forums, so I apologize in advance!

 

Try it without the resistor, see what the results are ...easy peasy

Larry

 

Larry,

For catmanboo's benefit, can you tell us if your oil pressure gauge is pegged at the top of the scale or does the needle stay near the middle?

Cheers,

Don

 

No it's not pegged or pinned, seems to read somewhat normally, rises with revs, about 1/4 or so on idle

Larry

 

Mine is hanging steady at 10 lbs after the resistor replacement. but at least I know the oil's flowing without having to pull the filler plug & watch the cams flinging oil. No idiot light. I suspect it's time for a new sending unit anyway. Doesn't vary with rpm. For the record, my car was made in may '94, last 6 of VIN 706184. Mileage just a bit over 113k. It sits for 6 months of the year, don't want to subject it to Ohio's crappiest weather. Yesterday, prior to firing her up after the long snooze,I pulled off the coil wire prior to starting. Cranked for about 20 sec. to bring up oil pressure. Reconnected the coil wire, touched the key, BAM! running like a beauty after sitting for 6 months. Wish it would do that on a hot start after sitting for a bit, like when running errands. I suspect fuel press. regulator. Cold starts usually ok, hot starts crank for a bit before the fires light. After the obligatory blue cloud, all's well!

 

Larry and catmanboo,

It's certainly possible that your '94s are equipped with the original transducer style oil pressure senders whose signal varies with oil pressure, but at some point, I think during 1993 or 1994 production, Jaguar changed to an "idiot light" switch style sender designed to keep the gauge's needle in a steady position - I think in the middle of the scale. The resistor on catmanboo's car clearly indicates that his sender is the switch type since the original transducers did not require a resistor.

A quick search didn't turn up the TSB for the six-cylinder cars, but here's the TSB for the V12s describing the change from the transducer to the switch and the "harness link lead" that was part of the kit. This short sub-harness placed a resistor in series with the sender:

Jaguar V12 Engine Oil Pressure - Incorrect Low Pressure Warning Repair Procedure 88-20

At some point, the transducer style sender was discontinued and only the switch style senders were available for replacement.

Cheers,

Don

 

With that late VIN# and resistor setup, you have a pressure switch fitted rather than a pressure sender. Very late models were fitted with switches rather than variable senders due to complaints of (apparent) low oil pressure readings/oil lights on etc.

Your gauge reading will be constant and centered when the engine is running - not fluctuating with RPM

It isn't really a variable unit, just an on-off lookalike. The X300's have the same switch system as the very late 40's.

My parts car @ VIN 703632 has the switch system like yours, while my Daily @ VIN 701729 does not, so I imagine changeover was somewhere in between.

Your oil pressure is probably just fine if the dipstick reads full.

Larry

 

Update: Today, fired 'er up for a trip into town, around 16 miles. Immediately on starting, gauge indicated 10 lbs. Well into the trip, it's now reading 30 lbs, varying ever so slightly if at all with RPM fluctuations. Maybe that bottle of STP cloud-suppressant I dumped in yesterday finally got diluted in the oil & the sending unit started seeing normal flow, I don't know, but I'm calling the resistor replacement a success. Gauge readings were always fluctuating, now are steady. Was likely that resistor crapping out all along. How its value jumped from 150 ohms to 730, I don't get. I learned something about the subject, I hope this experience helps someone pinpoint a similar problem with less screwing around than I went through. Thanks, guys for your input & replies! Jerry