Atlanta-area XJ40 experts (who like beer, ideally)

I’m a new Jag owner … 91 XJ40.

I just drove this car up the interstate to a work meeting 30 minutes away, and then back home on the back roads, and it was pure joy.

Well, except for two things: The AC doesn’t work so I had to go windows-down (which I don’t mind personally, but most passengers would), and when I stop at a light the oil pressure drops to zero and usually the oil dummy light comes on (I’ve recently started ignoring this as there seems to be no other indication of any issues, plus I’ve read about some sensor issues that are harmless).

There are other issues, like the occasional transmission light and limp-mode issue that seems random and usually goes away upon a stop and re-start of the engine, but nothing else really bothers me much.

If you are an XJ40 person in the Atlanta area and you would like to have a beer sometime, please let me know … I’m buying.

(Edit: Whisky works, too.)

I seem to recall in my distant Jaguar memory that the very low oil pressure did occur in hot ambient temperatures if the thin grade of oils were used. The factory fix was to go to 20W 50 and the issue went away. What oil viscosity are you using? The very thin oils were, I believed, specified to eek out a few fractions of MPG to get better EPA ratings and maybe reduce gas guzzler taxes. What is your oil pressure at say 2000 RPM hot. On my 73K mile 1990 XJ6 pressure is about 4.75 bar running 20W 50.

Funny you should say that. I just asked my wife to pick up some Castrol 20w-50 today while she was at the store … but she came home with 0w-20. Close, but not really!

The oil that’s in there now was in there when I bought it, but it does seem thin. I’ll try the 20w-50 and see how that goes.

It only dips to zero when it is warmed up and when it’s idling. The red oil light of doom comes on sometimes, too.

It idles ridiculously smooth (my first inline 6, so I’m still amazed by that) and there is no indication there’s any issue. Not sure what signs of trouble I would be able to observe, though.

At 1500 RPMs or above, the oil pressure reading usually hovers around the midpoint and I can relax and enjoy it.

Bill …

First don’t worry about the oil pressure. The XJ40 pressure transmitters are notoriously unreliable (that’s why Jaguar eventually replaced it with an off/on pressure sensor idiot light). I honestly in my 30 years of owning my '89 XJ40 can’t recall of anyone actually losing oil pressure in this bullet proof engine.

As far as your a/c system goes, although fairly complicated it’s extremely simple to troubleshoot.

1… When you turn on the climate control system (rotating the left knob from off) do the two fans under the dash come on and does the panel light up? If so …

2… Does the a/c compressor clutch engage. If you don’t know where the clutch is you’ve probably gone as far as you can troubleshoot.

3… If the clutch isn’t engaging make sure the control panel isn’t set to economy.

4… The clutch not engaging means either a bad clutch … or … the system is out, or very vey low on refrigerant.

Check on this and let us know what you find.

P,S. Castrol 20w-50 is the recommended oil.

Thanks, Grooveman.

I’ve read several comments about the oil pressure gauge issue, which is ther only reason I no longer freak out about it. Although it is still a little disconcerting. Hopefully I’ll feel better once I get the oil changed.

I’ll check out the AC as you suggested and report back.

(I do know what the compressor clutch is, by the way … and if I didn’t, I wouldn’t admit it.)

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OK, so I’ve been traveling a lot lately and only recently got around to changing the oil. The first time I started it after that, I heard an awful squealing noise coming from the engine, which went away after several seconds. It was similar to the classic fan belt squeal, except not quite; it sounded somehow more substantial, more like a screech, and far more menacing.

After the noise stopped, I took it for a drive and all seemed fine. I even got on it a little and it responded well. It seemed to run as strong as ever.

After a few days of sitting I checked the oil and it’s once again runny, dark and above full. It has a bit of a fuel smell, too.

I’m thinking the rings are bad. Does that sound about right? If so, is that a death sentence for this engine? And if so, are we talking about a slow death or should I be making arrangements asap?

Your harmonic balancer has delaminated (probably) - search archive for tests etc.

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Thanks for your reply. I’ve done a quick search around related posts re: the harmonic balancer, and you may be onto something.

My only question is whether the low oil pressure and oil issues that I’m having (oil thinning, level rising, smelling of gas) would be related to that, or if that would still potentially be a ring issue.

If your oil level is rising, but the oil is not milky and the coolant level not going down, and you don’t have blue smoke when you push on the gas, just watch it and see what happens.
The oil level increases slightly over a few days in most engines, as it all runs down over time.

Fuel smell is normal I‘d say and it will always be black quickly on all but new and well kept engines. Don’t worry about the rings.

The screech, balancer or belt most likely.

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If it only flickered, a change of oil to something thicker as soon as possible - damage is unlikely. At idle pressure is not that important and you still have a little bit of oil remaining in the bearings. After three seconds (an eternity) I tend to reach for the keys.

Unless the light flickers again I‘d leave it and it‘ll get a bit better at the next change, etc.

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Low oil pressure light on an XJ40 usually means nothing. Almost all sender units are worn out in a very short amount of time. Your oil pressure is probably fine.

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Oh, it’s not a separate idiot light in these? Then sorry.

Fresh oil change
9 quarts 20/50
Transmitters were terrible , clean contact or just get a new one about 20 dollars?
The a/c charge and pray if it holds your lucky if it doesn’t it’s a BIG BIG deal
Drive on the winter😃
Top off the transmission fluid
Low fluid can do that
Flush and change filter and screen
It wil help biggly
If not clean contact wires and ground at casing👍🏾
Enjoy the 30 year old ride!

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No David. It’s an actual sender. They get plugged up and show low. Almost all of us have replaced them at least once. Some owners replace it with the X300 style idiot light, not me though, I like to see the actual pressure.


I’ve checked this out a little more and I’m thinking I do indeed have an issue with the harmonic balancer – specifically, the outermost pulley that drives the AC compressor.

I can see that AC belt wobbling a bit while idling, and it doesn’t appear to be caused by the compressor itself, which appears to engage as it should and rotates evenly. I also notice it tends to steady when the engine is revved to mid-range RPM, whereas the other drive belts move nice and smooth throughout the full range.

As an interim step prior to tackling the harmonic balancer, I’m thinking about removing the AC drive belt to see if that alleviates the embarrassing screech that happens upon startup and maybe helps confirm my diagnosis.

Is that a bad idea, or is it safe to try?

My only worry is about having tension on only one side from the two remaining drive belts, but I’m not sure if that’s a legit concern or not. (I’m not worried about losing the use of my AC because it doesn’t work well enough in this heat anyway, dammit.)

Yep, most of us wishful thinkers removed the A/C compressor belt and some, (such as yours truly) even removed the compressor and bought compressor rebuild kits before a acknowleging the stark reality of replacing the balancer. YMMV.

So are you saying that removing the belt might temporarily stop the screeching upon startup, but that the harmonic balancer will continue to get worse until some miles down the road replacing it will be unavoidable?

I think you will find the screech will still be there.

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I’m afraid you’re right. Took the AC belt off and it’s just as bad.

This sucks.

I once had a belt screech on my 1990 XJ6 (circa 65K total miles) on start up and high RPM up around 4,000. Turned out to be a seized fan clutch that caused the fan to put too much load on the belt. Changed fan clutch and no more screech.