89 XJS Running on the Hot Side, No Oil Pressure at Idle

So what filter did you use? Make and number?

I don’t know that the filter type matters, (Mahle, Bosch etc.) I believe it is the filter size (larger) and the ability to flow larger volumes of oil. The larger filter I used recently I purchased a bunch of them off of one of the auto part websites as NOS clearance items and they are not name brand so I doubt one could find any more. The difference is if the gasket is up against the edge of the filter, or there is a half inch of space between the gasket and the edge of the filter (larger size).

When I get a chance, I can take pictures of both sizes for comparison. Thanks

Thx Matt. I knew you were talking about bigger size…more volume. I was curious to which filter you purchased. It is easier for me to go buy a known entity, such as repeating your purchase, than to just “go buy a bigger filter” only to find out it is too long or too fat to get it mounted. I was being lazy :grinning:

I agree with the bigger is better in this case

If you visit Rock Auto’s site, most filters size is listed in the “Specifications” Charts. The AC PF964 seems to be the longest at about 5 inches.
I have used Hastings LF 404 and LF 105, both of which are large filters, but they seem to be obsolete now, replaced by Baldwin 40120, which looks like the biggest filter available.(Longer than five inches.)

Thanks for your feedback. So what would the correct oil filter be for a 5.3 ltr xjs ? There are so many sites that show different filter. Which would be the correct one?

I can see this is an old post, but given the viscous clutch was free-wheeling, did you check to see if the bimetallic spring was exposed and clean.
The springs face forwards so become clogged with dirt so then fail to read the correct temperature so the viscous clutch fails to create the drag needed to drive the fan.

This is a fairly common issue with viscous fan clutch units.

Assuming the warning switch and gauge are accurate, you will only be able to see by physical inspection of each of the items.

Is the engine making any bearing type knocking noises?
You might be able to detect them better if using an engine stethoscope, after that, it’s sump off time.

Thanks Dave.

1 Like

I just bought a replacement one, but haven’t installed it yet. I plan on swapping out before it gets warm. Thanks.

Oil pressure is a function of a reasonably decent oil pump and tolerances between the bearings and the crank etc. As the bearings wear they get sloppier so instead of showing higher pressure, the oil is leaking out of the bearings quicker. Kirby’s book says that you , should not fear lower oil pressure on the V12 too much. As long as you have some pressure, oil is circulating around, though showing none at idle is a bit disconcerting. When I rebuilt one of my V12’s last year which had about 70k on it, the bearings looked fine, but the oil pressure prior to tear down wasn’t anything to write home about. When I had the engine apart, I ported and polished the oil pump housing as there was a lot of casting roughness and bumps. After figuring out the oil filter situation, I have a “lot” of oil pressure with that engine, in fact maybe too much as a leak has started where the filter housing mates to the block, this despite tightening the bolts which is really hard with the engine in the car. For my older engines, another thing I am doing is running 20w 50. Not a good idea if you are in a really cold climate and the car is not in a warm garage. That coupled with swapping out the fan clutch and a larger oil filter, I believe the problem likely will be solved. Thanks. P.S., on that engine rebuild, I had the crank polished at a machine shop and they also ovaled out each oil passage on the crank bearing surfaces. The theory on that is an ovaled hole is better than a round hole for getting oil to the bearings. It would be interesting to tear it down at 100k and see how the bearings look, though I doubt I will have time to put 20k on the car!

Thanks for your feedback.

No knocking at all. Engine is very smooth. Sump has been off because of suspected sludge on oil pickup but is was clean. I doubt the bearings were inspected.

Yet someone passed a comment about having the wrong /smaller oil filter which is my next suspicion which could make sense. Not enough oil flow therefore not enough oil pressure. I doubt it’s an oil pump because it’s such a big pump that I doubt it. Yet it still could be but a worn pump would give constant low oil pressure and not after oil warms up. After that I guess it’s engine out. Let’s see.


Undersize oil filter is a new one to me, but quite possible.

Shame the main and big ends weren’t checked, they are ultimately what causes low oil pressure.
The main and big end shells can probably be changed with the engine in situ.
Polish the crank journals and roll new shells in.