Strange oil pressure, help please

[malcolm]

In my post on my Ireland tour, I mentioned that the gasket between the oil filter head and the block blew out, resulting in all my oil being dumped. As well as pressure dropping to zero, there was a horrible mechanical noise on tickover as I pulled up before switching off. The engine probably ran for a few seconds? without oil.
New gasket fitted, and car runs well again. Engine sounds good with no horrible knocking or noises, but the oil pressure is not quite as it was. Two things happen:

Firstly, on a motorway at 3000 revs, (70), oil pressure was always 50-55. Now, it will run at 40-45. Then, after a while, it will move up to 50/55 and stay there. If I slow down so oil pressure reduces, and then speed up again, it will go to 40/45 again. Then after a while (ten mins or so) it will probably rise back to 50/55

Next, tickover was always 35/40 when hot. Now, it's 25/30 or could be lower on a really slow tickover.

I know oil pressure guages (mine is standard) are unreliable, but mine was always consistent and it's a bit of a coincidence that this started after the oil dump.

So, could I have damaged the engine? If so what? Although it sounds and goes great.

Could I have damaged the oil pump?

Or what else?

Later this year I'm driving the Spanish Pyrenees, and I'd like to resolve this before I go

Thanks in advance for any advice.

[1954Etype]

Malcolm,

first thing I would do is change the gasket for the correct type. There are lots of different gaskets used on the XK engines between oil filter housing and block. Get that right first then check. There could be a small hole covered, partially covered etc. Might not be the problem but best to baseline first.

[christopher storey]

Provided that the engine only ran for a matter of seconds after the total loss of oil, then although damage is possible, it is not very likely . Often, when the oil is drained for a change, and the filter is removed and changed, it will take up to 15 seconds for the pump to circulate oil through the filter and bearings, and you will get that nasty sound of bearing knock, but this does not result in damage. The new found variability in pressure is a bit strange, but could be accounted for by a number of factors e.g.

1. a different grade of oil e.g. 5w/40 compared with 20/50 would easily account for the difference

2. The makeshift gasket : this I would definitely change for the proper one, and make sure that you do get the correct one as different gaskets were used at different times with different filter heads

3. The pressure relief valve : again, I would definitely check this over or perhaps more desirably replace it, because something caused your filter gasket to blow, and it may have been a jammed PRV

If you are still concerned about damage, take off the filter and saw the element in half and look for metal particles in the oil and or the filter folds. Presence of metal is sinister, but if the filter is free of metal then you can be fairly confident that there is no damage

Good Luck

CTS

[malcolm]

Thanks both! The oil is 20/50, but not "classic" 20/50 that I normally get. Is was all that was available. It is mineral oil, and labelled for "older engines", made by Comma.

I'll get the gasket; I'm still running on the frosties gasket we made in the hotel car park! Maybe that is partially blocking something? The pressure relief valve - do you mean the one in the filter head? That is no longer available from SNG. Don't know where I might get one elsewhere. I'll look around.

[Heuer]

You probably don't need a new one, just verify the existing one is working. To do that put a clamp on the bypass pipe and check the gauge moves with engine running. All the pressure relief valve comprises of is a balance valve and spring but be warned that whilst removing it from the housing is easy, getting it back is a nightmare. The balance valve allows oil to be passed to the engine if the filter is choked with dirt. When this happens there will be an oil pressure drop of about 10psi. The balance valve is easy to dismantle and check.

[christopher storey]

Malcolm : the dissassembled filter head is shown at B.47 or the workshop manual . The PRV assembly is nos 15 - PRV , 16 - spring , and 17 - spider ; the balance valve , which is the by-pass valve, is 13 and again from recollection is a spring loaded valve, in this case a ball. You need to make sure that all of these are undamaged, have no breakages , burrs or the like which would make them jam, and that there is no particle of swarf etc which would interfere with movement. My guess would be that somewhere in these, there has been a foreign body which has blocked one or other orifices, thus leading to a sharp rise in pressure in one of the chambers which has blown the gasket

PS This crossed with David's post which says much the same

[Heuer]

[malcolm]

Thanks again both! Sounds like I've got a job to do. I'll have a go next week.