Oil pressure

[glenno]

Lads, (and perhaps girls?)

I've been advised of low oil pressure when hot! 4.0 litre XJ (1989). Everthing's fine when moving, needle drops when idling (but only when up to running temperature), is this electrical? Dodgy sensor? Or serious? Engine sounds fine. Anyone else experienced this? Feelin' a little edgy.

[triple7]

Have you got oil in it?

G :d

[rapidpete]

Hi, if the gauge is similar to the XKR it does not represent oil presure......it's just the same as the low pressure warning light..!! They are often faulty and pretty cheap to replace.
That doesn't mean don't check your pressure is OK it's just to say it's not a pressure gauge, just a switch..good luck
Pete

[Prof Beard]

What reading are you getting on warm idle? The oil gauge on the XJ40s is a real one. (The phoney ones were introdced later because the yanks were constantly going into their dealers asking why the readings kept changing - NOT a joke BTW)

Prof Beard

[glenno]

Prof Beard
Thanks for replying. I'll let you know what reading I'm getting tomorrow as I couldn't start it today!! Not having a great time with it at the mo, but very laid back about it - only way to be.

glenno

[railtracksport]

hi what milage has the engine done this is a comon problem with high mile engines but as long as its only at tick over do not worry to much unless you are prepared to give the crank a grind or a polish with new shell bearings

[glenno]

110,000 miles. (not warranted). That's helpful and quite positive though, thanks! I've a fuel problem now, likely to be the fuel pump as uncharacteristically noisey. (that must be one of the longest words I've ever written). Will know tomorrow. I will also know if I still have the oil pressure problem. Keep you posted.

[Prof Beard]

glenno - how's the oil pressure? My old 1990 4.0 Daimler sometimes droppoed as low as 10 on hot tick-over (as opposed to 40 on cold tick over), but ran nicely "in action" at between 50-60psi, and even on hot tick over would "pick up" to 30ish if you blipped the throttle. Never caused me any problems - engine was still fine at 140K when I got rid of it. (Sadly the self levelling suspension died and I could justify the cost of sorting it as tin-worm had got a bit of a hold as well)

[glenno]

Prof Beard. The garage are still sorting my fuel prob. It starts with an extremely rich mixture and then won't idle for long. The fuel pump is very noisey. They've put on a new fuel filter, I'm waiting for a call. Probably a new fuel pump to come. What do you think? I spoke to a Jag breaker who suggested 'sooting up' normally points at the airflow meter or the ECU. So can't comment on the oil pressure just yet, but will let you know soonest.

[Prof Beard]

glenno said:

Prof Beard. The garage are still sorting my fuel prob. It starts with an extremely rich mixture and then won't idle for long. The fuel pump is very noisey. They've put on a new fuel filter, I'm waiting for a call. Probably a new fuel pump to come. What do you think? I spoke to a Jag breaker who suggested 'sooting up' normally points at the airflow meter or the ECU. So can't comment on the oil pressure just yet, but will let you know soonest.

Take care - the fuel pumps on the XJ40s ARE quite noisy - also where they are sited means you can hear them more than in most cars. I guess the acid test is - does it pump properly? Someone with the kit can test the airflow meter or ECU.

[glenno]

Prof Beard

Picked car up today. Sorted. Fuel pressure regulator (£70) was the problem. The pump is now almost inaudible and the car goes like it should - fast and effortless. What a machine. I can see how owners become attached to them. The oil pressure guage seems to have sorted itself!

Glenno

PS mpg improved immediately.

[glenno]

Oil pressure drop returns!
Below 1000 rpm, the oil pressure guage drops to zero and the oil light comes on. The car is fine and shows no other problematic signs - temp stays constant ( middle of guage) and car idles fine. This only happens when the engine has warmed up, not before. Stil goes like a train if you want it too.
Prof Beard? Or anyone else of course.

[John Millar]

When was the oil last changed? Noting your fuel problem, the rich running could have dumped excess fuel in the oil, causing low oil pressure. Are you using 20w50 grade?

[Prof Beard]

glenno said:

Oil pressure drop returns! Below 1000 rpm, the oil pressure guage drops to zero and the oil light comes on. The car is fine and shows no other problematic signs - temp stays constant ( middle of guage) and car idles fine. This only happens when the engine has warmed up, not before. Stil goes like a train if you want it too. Prof Beard? Or anyone else of course.

Mine only ever did that when it was VERY hot (eg traffic queues on hot days) and only did it when I was stopped in gear with my foot on the brake, I never got below about 20 on idle even at 140K miles on the clock. The suggestion of changing to a different oil may be sound. How much below 1000 rpm are you going? I forget the normal idle speed but it wasn't much under 1000 if I remember right. If you "blip" the throttle on idle (out of gear) does it pick up or just drop straight back down?

[glenno]

John M
I don't know when the oil was last changed. No idea what grade was used. Perhaps an oil change is on the cards? It would certainly rule out your notion. What do you think?

Prof B
Idles around 750 to 800 rpm. I haven't tried blipping out of gear, not consciously. I'll have a play tomorrow.

Thanks for the response lads.
Glenno

[john millar]

I think you might do well to get some good quality 20W50 in there.
See if the oil that's in there seems very "thin" or smells of fuel.

[glenno]

John M
Haven't had chance to check the oil viscosity/ smell yet, but will do.

Prof B
The oil pressure guage drops only when engaging 'drive' at idle. In 'park', it rises back up to normal with no help from the throttle. Verdict?

Glenno

PS Please don't say "sell it"!

[Prof Beard]

glenno said:

John M Haven't had chance to check the oil viscosity/ smell yet, but will do. Prof B The oil pressure guage drops only when engaging 'drive' at idle. In 'park', it rises back up to normal with no help from the throttle. Verdict? Glenno PS Please don't say "sell it"!

Unless changing the oil solves it, I would be tempted not to worry, but to put the car in "N" whilst standing. ie in a queue of traffic, put you foot on the brake as normal, them move the stick to N, on moving off, stick it in D and then prees the accelator. It should leave the car at low proessure for any significant amount of time that way. I used to have to do that with mine in jams in hot weather, never got worse that that.

[w824gb3]

Your low oil pressure is probably just a bad sender. It's very commmon on the later x300 models & I guess yours uses a similar unit.

[glenno]

How would I test a sender unit?
I'm about to change the oil anyway as it looks rather black and thin. 20w50 grade was suggested. I have also been advised to use 15w40. Is one more suitable than the other? What about synthetics, are these OK? All suggestions welcome!