Is my oil pressure too low?

[GeordieDave]

From cold, the oil pressure drops from 50psi down to what looks like 10psi at idle when warm. Is it time to take action or am I OK? [frame][/frame]

[liammonty]

That is low, to be honest. At normal running temp after a good long run, my recently-rebuilt engine holds around 40 psi at idle, but that is with very little wear. I guess your engine is tired, but if it is still running OK, with no knocking etc, I wouldn't worry about it. If you didn't have an oil pressure gauge, you wouldn't even be thinking about it! That said, it may be time to put some money aside for an engine swap in the future.

Two other things - are you using 20W50 or similar (i.e. not a very thin oil, and not a monograde), and do you know if your oil pressure gauge is accurate?

[GeordieDave]

Hi liammonty - thanks for the quick reply. The engine idles very quietly and I don't hear any knocking at speed - above all the other noises! Also, there's no blue smoke from the exhaust. The car has been off the road for a few years until recently, but I remember the pressure was always low, it hasn't dropped in the last few months.

I don't know what oil has been used as the car was serviced at Millennium Minors in Manchester so I would have to ask them. When they MOT'd it last week they said it was very well tuned and running well.

I have no idea how accurate the gauge is - it came with the car. Is there a way of getting an accurate reading? The car is a 1962 948cc.

[bmcecosse]

The pressure when running along at 50 mph in top gear is what matters - as long as it is 50 psi then it's ok. Not 'fantastic' but a good few miles in it yet.

[liammonty]

Hi liammonty - thanks for the quick reply. The engine idles very quietly and I don't hear any knocking at speed - above all the other noises! Also, there's no blue smoke from the exhaust. The car has been off the road for a few years until recently, but I remember the pressure was always low, it hasn't dropped in the last few months.

I don't know what oil has been used as the car was serviced at Millennium Minors in Manchester so I would have to ask them. When they MOT'd it last week they said it was very well tuned and running well.

I have no idea how accurate the gauge is - it came with the car. Is there a way of getting an accurate reading? The car is a 1962 948cc

I really wouldn't worry if it's running nicely. I suppose the only way to check the gauge would be to swap with another and see if that read the same, but there's really no need if it's running well - as I said, if the gauge wasn't fitted, the thought that there might be a problem wouldn't have even entered your head, and you'd be merrily driving around with no worries. Don't worry regarding the oil either - it wouldn't make that much difference. The main thing is that it has oil in it!

[dalebrignall]

as long as you have some pressure at idle its fine

[biomed32uk]

May be worth a check of the pressure release valve, sounds a bit low if its only 50 cold. My engine was fairly worn and would still do the 75 cold, falling away when hot at idle.

If the pressure relief valve is worn, weak or not seating properly then it will low right across the range which it seems to be.

Easy to get at and be worth a cursory glance

[twincamman]

I would try replacing the spring in the relief valve and see if that improves matters.

[bmcecosse]

Highly unlikely....still to hear what the hot running pressure is.

[MikeNash]

A few thoughts, Geordie.
The electric gauges are cheap, reliable and easy to fit but not so accurate as the capillary and pressure gauge type. And further, the sector of interest, 0-60/70 psi is squashed on yours into about 45 degrees whereas my Smiths pressure gauge covers some 180 degrees for that pressure range. So yours is inherently more difficult to read. But that said, the blow-off pressure of the relief valve is almost always about 60 psi when the oil's warm and about 65 even 70 with a dead cold engine, and if we take this a true for your engine then we might guess a calibration for you, i.e. your reading of 50 psi equates to a true reading of 70, and if so, then your idle of an apparent 10 might a true 14. If all this is true, I'd be content.
But that said, if your engine isn't knocking or otherwise noisy, like Mr Liammonty I'd recommend you don't worry. My previous engine which only gave 42 psi when hot and which would fall to 8 psi when idling, while not the quietest it had no obtrusive noises and could cruise for hours (literally) at 60-65 mph without distress. (But it drank oil!)
Regards, MikeN.

[liammonty]

One of my biggest mistakes was fitting gauges to my T2 (air cooled) VW, which has none bar a speedo and fuel gauge as standard! It had always run well, and I'd never worried about until that point, but then I found myself constantly worrying about it being too hot, or the oil pressure too low. The best thing to do with your gauge is just to pay attention to its 'normal' range, and the day it starts to read significantly differently to how it normally does, take that as an indication of a potential problem. Otherwise, don't worry, as MikeN says!

[bmcecosse]

And hopefully the engine you have now Mike holds good pressure, and doesn't burn oil now that you have finally sorted out the breathing problems !! I wouldn't be so sure about that calibration reasoning....it may not be linear... STILL KEEN TO HEAR THE HOT RUNNING PRESSURE!

[GeordieDave]

Thanks for all your input. I'm working away at the moment but when I'm back home I'll have a good read through and take the car out to get it warned up for the all important hot pressure. Thanks again

[bmcecosse]

Ah right. Let us know in due course!

[GeordieDave]

Hopefully I'm in the clear? This is the pressure at 50mph after 30 mins [frame][/frame]

[Boomlander]

That's about the same as I get when driving.

[bmcecosse]

If the gauge is accurate - then sadly a big fail. It should be 10 psi per 10 mph up to 50/60 mph... You could try another gauge.....but I suspect the bearings are worn.

[biomed32uk]

Agreed, if the gauge is right then its way too low if thats what you are getting running along. I get about 60 PSI hot at 50 mph or so, and thats on running in oil which is straight 30 grade.

Surprised you can't hear it complaining some when you push it a little, I did with worn mains.

[MikeNash]

Dear Geordie,

I'd like to know what you get on first start up when the oil's cold. If you blip the throttle what does it ready then? Like I said in my piece above, I'm trying to "calibrate" your gauge. If I read you photo right and you're getting about 30 psi AND my previous suggestion is correct that your gauge is under reading then you might have about 40 psi. Not the best by a long way, but more "liveable with".

As I said before, my previous engine ran like this for years (on Wilkinson's SAE 20/50) and if your engine doesn't make much noise I'd live with and steadily collect the bits to do an overhaul or replacement when it suits you.

Regards, MikeN.