The car runs great, just barely can tell it's running at a stop, in drive when fully warm. My oil pressure gauge is driving me crazy. It's at 5 when driving at 3k rpm as it should. When she is cool running, before it's ideal temp is achieved, the gauge appears normal. At a stop it's at maybe 2. But when it's hot 90+ degrees and in stop and go traffic that gauge sits below 2, and just a bit in the red. No oil light though. Oil is fresh and full. Why is this? She goes right where it should while driving though.

 

I presume you mean "50" rather than "5" ?




As far as I know your 1992 will have the old style barrel gauges, yes? If so, these are very flaky. The sending units can give trouble, as can the gauge itself or the printed circuit on the back of the instrument cluster.

All that being said....

It's typical for the Jag V12 to have very low oil pressue at idle when hot so you could very well be chasing a non-problem. Mine used to just touch the "0" on the gauge at idle but zip up to 50psi when the throttle was opened a bit.

Attaching a hand held mechanical oil pressure gauge to verify the readings is one option.

Cheers
DD

 

Hi
I have a late 1993 4.0 litre Coupe and I am having to fit a new oil pressure sender every year as they keep failing; all of a sudden the gauge will drop a bit and then go up and down like a yo-yo. I would recommend as a matter of course taking your car to your nearest friendly garage (unless you can do it yourself) and have them put a remote gauge on the sender take off just to check that you do have pressure.
If their gauge shows a good reading right through the rev range then it is probable that your sender is at fault. If their gauge does the same as yours then you may have pump or flow problems.
I get my oil pressure checked manually at every service as I don't trust the sender.
Don't totally rely on the warning light as damage may already be happening by the time that illuminates and of course the bulb may be blown!
Steve

 

Nope...don't change any parts, what you are seeing is completely normal. In fact if you read your owners manual it even mentions that low oil pressure on the gauge, hot at idle is normal and nothing to worry about. In later years, they "fixed" this problem by fitting a sending unit that makes the gauge read normal, or nothing. As long as your light works (comes on when you turn on ignition, but goes out after start, and doesn't flicker, or come on while running), then everything is fine. I agree it is bothersome, but I have had 3 Jag V12's over the years for long periods (my curent XJS 6.0L has a shade under 200K miles), and they all behaved that way after about 65K miles or so.

Dave
Atlanta

 

Hi Dave
I'm not disagreeing with you but how come my gauge always reads correctly (i.e .consistently) whenever I have changed the sender?
I would still get the pressure checked for peace of mind.
Steve

 

Two issues are being confused, I think.

What Talkradio is describing is most likely not a fault at all but, rather, normal behavior for a V12.

What you've described on your six cylinder car is a different matter.

Cheers
DD

 

@Talkradio

Your condition sounds perfectly fine for a 92 V12. Mine does exactly the same thing as yours.

I also have an oil temperature gauge in the car, with the sender braised into the sump...... basically my oil pressure gauge and the oil temperature gauge are inversely proportional to each other at idle, ie when the oil temp is high (It can get up to around 190degrees when idling) then oil pressure is showing pretty much zero on the gauge. It's also an interesting exercise to compare the water temp and the oil temp...... it takes much, much longer to get the oil up to temp than the water up to temp. I used to think it was ok to use full performance once the water temp was up, but at that point, the oil is still far from warm......

 

I thought the '92 and later had the "all or nothing" oil pressure sender, i.e., as long as there is adequate pressure the gauge will read the same. The gauge on mine and I assume all facelifts is the traditional style (not barrel) with a scale of 0 to 8. Mine reads right at 5 all the time, idle or full out, cold or hot.

 

AFAIK early face lift cars still have the "real" oil pressure gauge. However, Jaguar (and, eventually, outside vendors) no longer offered the original style sending unit.....and replaced it with the "dummy gauge" type sender. So....cars that had originally had a true presure gauge generally end up with a "dummy gauge" a few years down the road when the sending unit fails and needs to be replaced.

The early 1995 X300 sedans had a true o/p gauge but Jaguar went to standard fitment of the "dummy" sender early-ish in the model year. I wouldn't be surprised if the same change was made to the XJS at about the same time....probably late in calendar year 1994.

Cheers
DD

 

I can't say for sure...but I am fairly confident that the XJS always had the real sender, and that the dummy was only fitted to later X300 sedans as you mentioned.

Dave
Atlanta
1994 6.0L

 

I have a real sender for sure..... This dummy gauge thing is annoying. On newer Jags they even did it with the Temperature gauge !! Whats the point of the gauge then ?!

 

Sadly, Sarc, (as I am sure you realise) it is just marketing. People like gauges, but it is cheaper to give them idiot lights disguised as gauges, so that is what they get. And, of course, the majority do not know they are being short-changed, and why should they?

Just another example of amoral corporate behaviour.

Greg

 

The mechanic said that they are basically on/off switches and just show that there is some pressure there. On my late '93 Coupe I am sure that the gauge goes up to 10 and the reading sits at a constant 8; or maybe it goes up to 8 and sits at a constant 6. Anyway, every year so far it has started wobbling around so replaced the sender and it is back to steady again. I am guessing shoddy reproduction parts.
Steve

 

Heh heh. Where does that leave us with nylon that looks like wool, vinyl that looks like leather, plastic chrome, wheel covers that look like alloy wheels?

I guess anything disguised as one thing but being another can be discussed as a morality issue....although far worse examples of corporate immorality can be found. But now I'm getting into "moral relatavism"....oy ! Danger, danger ! :-)

But, back to gauges.....

I reckon dealer personell were tickled when Jaguar (among others) went to the "dummy" gauges. Thus endeth the almost daily phone calls from customers who go into freak-out mode every time the temp or oil pressure needles moved a fraction of an inch! I spent years dealing with these customers.....scared, confused, sometimes angry. What a time sponge ! I truly think this was the motivation behind the dummy gauges.....to assuage the worried minds of confused consumers and putting an end to decades of their hand-wringing.

But, yes, manufacturers who simply eliminated oil-temp-volt-amp gauges entirely were being more honest. More honest = more moral so, at the end of the day, you're right :-)

Cheers
DD