Oil Pressure

[470HW]

I'm worried about the oil pressure on my MKII 3.8 litre. I've read from various sources that the oil pressure gauge should read 40 psi at 3000 revs/minute. When the car is hot the gauge just about makes it to 40 psi at 3000 revs but when the car is ticking over it reads 0. A slight blip of the throttle brings it up to 20 psi. Should I be worried about this or is it normal.

[oldtimer]

40psi at 3000 rpm is fine. Done put too much faith in the gauge. Can't remember off hand if it is a wet gauge or electric. Electric ones can be a bit iffy

[PPV]

The electric gauge is a bit iffy. Does the oil light come on also? The only way to check is to connect a wet connection gauge to see exactly what is happening but can you hear any noises at present that would indicate wear in bearings etc? It is unlikely oil pressure has just gone unless there has been a catastrophic failure somewhere. It is usually problems with the sensing end but not sure how you check it.
Regards,

[peterdpps]

On my 240 it is an electric gauge. Original sender showed lowish pressure especially when hot. Had pressure checked by a wet test unit then replaced sender with a new one. The new electric sender tends to read high, up to about 70psi I think at 3000 rpm.

[grumpypete]

I had (have) exactly the same issue with my 3.8. As peterdpps says, the gauges and senders can give very inaccurate readings. I have heard horror stories of people spending thousands rebuilding their engines because of low oil pressure, and getting no improvement because it was a dodgy gauge or sender all along. I bought a mechanical gauge to check, and it also showed quite a low pressure. I know now that I should have replaced the 57 year old oil pump when I had the sump off! For the moment I am running on 20/60 which seems much better, especially in hot weather. I consider anything above zero quite acceptable at tickover hot, and 30 psi at 70 mph a bonus, but then the engine has done 115 k miles. What we should bear in mind is that very few cars have had the luxury(gimmick) of a pressure gauge, and relied on a pressure switch and light. To my mind, much easier on the nerves. Perhaps that should be my next modification!
Regards,
Pete.

[Tintin]

Does anyone know if you can get a "wet" gauge with an identical face to replace the Jaguar electric gauge? The nearest I have seen is a similar Smiths unit reading in both metric and imperial with a maximum value on the printed scale of 100 PSI.

Robbie

[470HW]

Thanks for the responses. Now I've driven the car for a few hundred miles more it seems worse than I first described it. When the oil gets properly hot the gauge reading stabalises at around 20 psi @ 2500 revs. Doesn't go much above that and hovers just of zero at tick over. Given the comments so far and given that the engine sounds happy I don't think I'll take any drastic action at present. I'll probably get a reading from a more reliable wet gauge and replace the sender at some point in the near future though as it seems like the most sensible first step. Will post the results and thanks once again for the advice.

[SimonF]

Does anyone know if you can get a "wet" gauge with an identical face to replace the Jaguar electric gauge? The nearest I have seen is a similar Smiths unit reading in both metric and imperial with a maximum value on the printed scale of 100 PSI.

Robbie

Yes Robbie, mine has a correct 60psi wet Smiths gauge.

Simon

[Tintin]

Yes Robbie, mine has a correct 60psi wet Smiths gauge.

Thanks Simon. Where did you get it - or did it come with the car? I would like to replace my electric gauge with a wet one but only if the appearance is identical.

Robbie

[PPV]

I have thought about changing mine and perhaps buying one from one of the specialist suppliers and change the face over from my current gauge. Such suppliers as : http://www.jjcraceandrally.com/kit-car/ ... cal-gauges or https://www.carbuildersolutions.com/uk/ ... tubing-kit could have something that fits, is reliable and accurate. I know the back of it is not original but perhaps that is a price you have to pay for accuracy.
Regards,

[PPV]

I forgot to mention the likes of Holden do original types also : https://www.holden.co.uk/displayproduct ... m+Quadrant
Regards,

[Ronniebiggs]

Many aeons ago, some Standard Triumph cars were fitted with oil pressure gauges. They were pestered by service complaints of low oil pressure at high revs; investigation showed that the oil was being 'centrifuged' out of the bearings but full lubrication was maintained.

They stopped fitting gauges. Service complaints stopped too.

Oil temperature would be a more important reading...

[Tintin]

Oil temperature would be a more important reading...

I (and I think most folks) use oil pressure as a rough indicator of engine wear - a significantly incorrect pressure reading may be misleading (hence my quest for the more accurate wet gauge). How does oil temperature indicate engine condition?

Thanks for your suggestions, Paul - I will look into this.

Robbie

[Ronniebiggs]

Oil temperature getting too high can be a symptom of a few things - over-filling (windage puts a lot of energy into the oil) and bearing surfaces picking up are two, but low levels in the sump mean the oil you have is worked harder. Extending an engine before the oil is up to temperature is inadvisable as it indicates the engine internals are not fully up to temperature and therefore not at correct running clearances. I know it's rare for an XK engine to run too cold, but if the engine isn't run fully up to temperature you also don't boil off the water which can collect inside. This is more of an issue when cars are only run to move them out of the garage and back again, in the misplaced belief that starting it up occasionally is good for it. If you're going to start it, drive it - get it up to temperature quickly by driving it under a light load rather than ticking over in the drive. If I want to move mine out of the garage temporarily I use the overriders and pull...

In period it was said, with good reason, you did more wear on the engine starting it up than you did on the 100 mile drive which followed.

Generally I'm of the opinion too many gauges give you things to worry about. A good speedo to keep within the law and warning lights for things amiss will generally suffice. If the engine's badly worn you'll hear it; on old engines in the past I've known of 'healthy' oil pressures with one big end making enough noise to waken the dead! My 3.4 has 117 k miles on it and rarely gets to 40psi but then it's rarely above 3000 rpm. In overdrive top that's more than enough...

Jay

[Volvo]

Greetings, pardon my ignorance, but can anyone tell me where the oil pressure sender is located on the 3.4? All of the posts about oil pressure are familiar to me - the engine has done only 7k since a complete professional nut and bolt re-build - runs beautifully and no worrying noises.
Richard