Hi Folks on my 1986 xj6, the oil pressure reading would drop to the lowest point on the gauge when she sat at idle when warm, so I changed out the oil switch, and now she reads fine at idle —a little before the 40 mark, but when I drive her she will all of a sudden go beyond the 0 mark and then jump back up to the 40 mark, so in other words she is jumping back and forth, no stalling , no overheating no nothing , running just fine, just an erratic reading on my gauge, and my oil level is fine
Three theories:
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A jumpy sensor. They are kinda weird.
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A poor connection at the sensor or at the guage.
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Bad wire/s.
A. Power source the guage
B. Sensor to guage wire.
Try.
With great care and engine running, and an observer in the cabin, wiggle the wire.
Carl
1 Like
I agree with Carl. First look at the wires. The wires in that area take a beating over the years
Cheers
DD
Dieman,
I hope you kept the oil pressure sender that you removed. It sounds to
me that the one that you removed was acting properly. It should read it’s
lowest when at idle after the engine is warmed up. I suspect that the new
sender you installed is bad. If this happened to me I would first inspect
for any obvious wiring problems around the new sender but absent that I
would reinstall the original sender to see if this makes the needle jumping
around goes away. If it does, just leave your original sender in there and
return your new sender for a refund. Just because it is new doesn’t mean
that it works properly. I have had brand new parts fail for me right out
of the box. Others have reported on Jag-Lovers about failures of new
aftermarket oil pressure senders.
The normal behavior for the oil pressure is for it to be higher right
after you start the engine from a cold start because that is when the
viscosity is the highest. The oil gets less viscous (thinner) as it heats
up and the oil pressure should drop particularly at idle once warmed up.
The oil pressure gauge Jaguar selected to install in these cars is not a
precision instrument. If you want a precise reading you will have to hook
up a modern sender and digital gauge. As long as you are getting some
reasonable consistent readings and the oil pressure light is not on when
the engine is running (and illuminated when the engine is off), your
original sender and gauge are fine. The only oil pressure test that I am
aware of for the Jaguar 4.2L XK engine in a Series III XJ6 is at 3,000 RPMS
after the engine is warmed up. The reading in that state should be at
least 40 PSI. This test can be found in the Series III Handbook owners
manual. Practically speaking I’d say that 40 PSI would be ideal, but if it
was a little lower than than I would not be concerned especially since the
gauge isn’t that accurate and pressure will drop as the engine wears with
use. BTW that 40 PSI is with the correct oil which in my location is
20W50.
Paul
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I second Paul, Dieman - idle oil pressure low in idle is normal, the same oil pressure both in idle and at speed is plain wrong…
The ‘proper’ procedure with a suspected low oil pressure is to measure it with an external gauge - to verify readings. Changing the switch does not alter pressure itself - it may just give false security.
If the original set-up gives minimum 40 psi, or thereabouts, at 3000 rpms - it implies acceptable pressure, and a properly working set-up. If in doubt, a separate pressure check is advisable - but to let he matter rest because the ‘new’ switch gives 40 psi in idle is premature…
Certainly, there may be a separate fault causing the intermittent readings - or a plain faulty switch, as Paul implies. And his advise is good…
Frank
xj6 85 Spv Europe (UK/NZ)
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Thank you for the valuable info, I did reorder a new switch and am having the darness time locating the original switch which I put in the new senders box and placed it somewhere in my garage, hope to locate it soon, but Thanks you very mucho Paul
Paul,
I have a 74 Series II that is giving me similar issues, good pressure at start, and then drops off below zero as the engine warms up to temperature. Unfortunately, the sensor was replaced by a mechanic and I don’t have the old one to put back.
I have the Series II manual and the Haynes manual but am unable to find any info on how to perform this pressure check, which port to use, what tools are required, etc. Paul, Is the Series III manual you speak of available online through JCNA or other clubs?
Appreciate the help.
-Kurt
Kurt,
That test, 40 PSI at 3,000 RPMS is shown in the Series III XJ6 Owners Handbook, the owner’s manual provided to the owner of the cars when new. This is not the Service Manual or Repair Operations Manual (ROM) although it might be found there as well.
I have a problem similar to yours with the high mileage 4.2L XK engine in my 1969 E-Type. Decent oil pressure at start but once the engine is all warmed up the original oil pressure gauge appears to read “0” when at idle when I am sitting a stop light. I purchased a modern aftermarket oil pressure sender with a digital display and installed it with a “T” plumbing adapter to the original sender fitting on the right side of the block. I installed the gauge in the dash in place of the clock. So now I can compare the original analog and new digital oil pressure readings while driving. This is especially comforting to me while sitting at idle with the engine warmed up since the analog gauge show maybe 0 or 1 PSI but the digital gauge show a fluctuating range of from about 7-12 PSI. Because it is not 0 and fluctuating I am confident that there is oil being supplied to the engine. At 3,000 RPMs they both show oil pressure in the high 30s which I am living with for now.
If I were you I would consider installing a modern oil pressure sender with a digital display and see what you get for oil pressure readings.
Paul
Paul,
You describe exactly what is going on with my car right now! I had an oil analysis done and the results were cautionary. The presence of these materials could be explained by the introduction of oil additives, which I understand were added, but it could also be symptomatic of worn bearings.
Were you able to purchase one of these modern units at an O’Rielly’s or Autozone, or is it more “boutique”?
Thanks for your reply.
-Kurt
But if the values are like that (okay when cold and very low when hot) I would check, re-check and shim the relief valve that can get stuck open. It dumps oil straight to the sump and failed me twice in a year ond the S3. I had 40 cold, 0 hot idle and 10-20 when driving. Now it’s at least 15 at idle and about 45 at any other time again.
Of course it can be the gauge or the worn engine, and certainly you already considered the valve, but maybe you or someone else missed something. Don’t ever try to clamp the little return hose, it will just blow off.
Kurt, there is not much “botique” about it, it gets a voltage from a sender (thread sizes…) and translates that into pressure. People will tell you to get a good one though!
David
New oil pressure switch did the job, they switched it out for me, and she is doing fine now
Kurt,
I added the digital oil pressure gauge a while back but it seems to me I purchased it online, possibly through JEGS Autoparts or JC Whitney. It wasn’t expensive or high tech. I was simply looking for a redundant oil pressure sender and gauge to see if I had an oil pressure problem or an indicating system problem.
The attached pictures should help. One shows the gauges with the car at operating temperature at speed with the digital gauge showing 32 PSI and the original gauge showing about 16 PSI. The second shows the gauges at idle with the digital gauge showing 13 PSI and the original gauge showing about 0. The third picture shows the “T” adapter with the two senders connected up. The original sender has a pipe thread and I shopped around at a local hardware store with the senders in hand to find a threaded “T” that fit.
I suppose that I may simply have an original oil pressure gauge or sender that is out of spec. But for now I am satisfied with the side by side readings and will continue to drive the car this way unless I get secondary indications of an engine problem.
Paul
Dieman,
So it looks like the first replacement oil pressure sender failed right out of the box and your second replacement oil sender worked properly. Is that correct?
If it is it is another example of brand new parts, specifically oil pressure senders, failing.
Paul
Yes that is what happened, they gave me a replacement and it works fine now
Paul,
Can you confirm for me that what you have pictured is the “Oil Pressure transmitter” which sends a signal to the “oil pressure gauge?”
I’ve submitted two pics, in the first pic I have some questions about the relief valve that can be prone to being stuck open. I’ve had the encircled piece off, and indeed there is a valve and a VERY heavy spring. I removed that assembly inspected, cleaned, and reassembled. Even if it was “sticky” I can’t imagine that it would be the issue.
Of note, even though this is a Series II, I’ve fitted the engine with the spin on adapter.
Really appreciate all the advice from the forum
.
Dieman,
Ok, thanks.
Paul
The most reliable way to get an accurate oil pressure reading is to use a wet line gauge. There’s far less to go wrong on a wet line gauge. Any XK engine with 15psi on tickover at NWT needs some serious inspection of crank bearings and oil pump.
It’s not going to get better - only worse maybe until there’s a big bang and a rod peeps through the side of the block!
**
A separate external sensor should be used for testing, Kurt - the one you have may be faulty or the wrong type…
There is also a secondary indicator; the oil pressure switch - which nominally lights the warning light below some 3 - 5 psi. If it comes on with the key to ‘run’ before cranking - and is not on while the engine is running; the pressure is likely OK.
As Paul says; specs are ‘minimum 40 psi at 3000 rpms’. It’s then perfectly normal that oil pressure falls as the engine heats up, and is low at low idle hot - but without a verified gauge; all pressure readings are meaningless…
The oil pressure ensures that the journals are supplied with oil, to provide lubrication and cooling by circulation - with adequate oil supply to the journals the pressure itself is immaterial.
You do not mention the viscosity you use; one counter to low pressure is to use thicker oil - up to a point. The higher viscosity with cold oil reflects this effect - but with excessive wear, or a leak, it may reach a point where higher viscosity is counterproductive.
Be also aware that the pressure is measured after the oil filter - a clogging up filter will reduce fuel pressure.
You can hook up an external pressure gauge either at the transmitter tap-off, or at the pressure switch tap-off. But actions taken before oil pressure is independently confirmed are premature…
Frank
xj6 85 Sov Europe (UK/NZ)
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Frank, Thanks for your reply. I am convinced now that the next step is to get an accurate oil pressure reading, before any more analysis can be done.
-Kurt