13 replies to this topic

[Robert]

Model: Cooper
Year: 1998

I've done a search, but I can't seem to find out the answer. I guess I am probably not looking hard enough!

Last time my Dad came to visit, he presented me with a Smiths Oil Pressure gauge that he had found laying around in the shed, with the comment "This is probably of more use to you than to me". He'd bought it years ago, and it came complete with the T-piece, pipe, unions, everything.

I've fitted it today, and it is working beautifully - but the (rather embarrassing) question is, what oil pressures should I be getting? I'd like to think they are Ok because she's just had a complete rebuild - but it would be nice to know what I should be expecting!

[Ethel]

The pressure doesn't really matter, it's just an indication that the oil is being pumped into the bearings faster than it escapes. Ideally it will very quickly rise to whatever opens the pressure relief valve (30psi would be sufficient, most make 50-60) and stay there. If the pressure drops at low revs or when the engine warms up it tells you more.

[dklawson]

What is "good" oil pressure is always a topic of discussion and debate.

What you should be aware of now that you have an oil pressure gauge is that the pressure is not going to be constant. You can expect the pressure to be high when the engine is cold, high when at speed, and possibly quite a bit lower at idle when the engine is fully warmed up or hot. The pressure is influenced quite a bit by the engine speed and engine temperature.

Keep this in mind and don't panic when this summer you observe significantly lower oil pressure when sitting at a stoplight.

[Robert]

Thanks very much.

When the engine is cold, she's idling with around 70psi, this drops to around 60psi once warmed up.

Of course, the pressure fluctuates while driving - but I am keen to keep a close eye on oil pressure, as I don't want my new engine to go the way of the old one. (Although that was probably more to do with oil change frequency by the previous owner )

[Cater_Racer]

Over 50 psi when over 2500 rpm warm is good enough, dropping to 20-25 psi at tick-over (1000rpm) warm is fine, using 20-50 oil.

Lower than that means wrong oil/lower oil/warn bearings/ tick-over set too low.

If it's very warm HOT, then @ tick-over down to 15 psi, still nothing to worry too much about.

HTH

[starletman]

Thanks very much.

When the engine is cold, she's idling with around 70psi, this drops to around 60psi once warmed up.

Of course, the pressure fluctuates while driving - but I am keen to keep a close eye on oil pressure, as I don't want my new engine to go the way of the old one. (Although that was probably more to do with oil change frequency by the previous owner )

Have you also fitted the 23lb oil pressure switch.That way if theres a problem the oil light will come on before any damage is done.

[bmcecosse]

Your pressure is fine - that gauge is essential kit for any A series engine!

[Robert]

Have you also fitted the 23lb oil pressure switch.That way if theres a problem the oil light will come on before any damage is done.

I haven't - but to be honest, the gauge is easier to see than the light!

The gauge has been mounted where the clock used to be, but the light is hidden behind the steering wheel.

[dklawson]

I am not a big fan of using higher set point pressure switches.

While it is true that you will get a low pressure warning earlier with a different switch, note Cater_Racer's comments earlier that idling with 20-25 PSI with a hot engine would be acceptable. If you fit a 23 PSI switch you might see the warning light coming on at idle even though all is well. That's OK... but subliminally it teaches you to ignore the light.

I had this problem last year with our Triumph GT6. It was a particularly hot day and my wife and I were returning from a car show. My wife freaked out when the oil light came one. I had installed a 20 PSI switch in her car and the idle oil pressure was hovering around 18 PSI. It was safe enough to drive as the oil pressure came right up when the engine was revved... but the light still scared my wife to death. There is a reason the car companies selected the pressure switches they put in our cars when new.

[Sleepy Stu]

I am not a big fan of using higher set point pressure switches.

While it is true that you will get a low pressure warning earlier with a different switch, note Cater_Racer's comments earlier that idling with 20-25 PSI with a hot engine would be acceptable. If you fit a 23 PSI switch you might see the warning light coming on at idle even though all is well. That's OK... but subliminally it teaches you to ignore the light.

I had this problem last year with our Triumph GT6. It was a particularly hot day and my wife and I were returning from a car show. My wife freaked out when the oil light came one. I had installed a 20 PSI switch in her car and the idle oil pressure was hovering around 18 PSI. It was safe enough to drive as the oil pressure came right up when the engine was revved... but the light still scared my wife to death. There is a reason the car companies selected the pressure switches they put in our cars when new.

While I agree with some of this; say you didnt have a gauge to check. Would you want to be warned when you pressure is below 8psi. By the time you have actually seen the light think of the damage that could already have done? For piece of mind I have both the higher pressure sensor and a gauge that way if I should catch the light popping on its a prompt to look at the guage and see if there is a problem or if its just a hot day.

Edited by Sleepy Stu, 23 January 2011 - 01:11 AM.

[Spitz]

Haynes even lists normal oil pressure at idle ( hot ) at 15lb's.....so don't woory too much if it drops beloew 20Lb....especially after a long run....absolutely normal.
My owner's manual states 15lb also.

[dklawson]

Sleepy Stu, I have only the gauge in the Mini, gauges and lights in both Triumphs. I don't disagree about low oil pressure at speed causing damage. However, where do you draw the line when fitting a higher pressure switch?

[starletman]

Sorry to change subject slightly but is it possible to have too much oil pressure and if so what would be to much.

[bmcecosse]

Yes - it is possible if the relief valve has been set too high or is jammed shut(unlikely!). Withe cold engine the revs should be kept down to allow the oil to thin out - and to keep the pressure below the max reading on the gauge. If the gauge goes higher the mechanism is likely to be stretched and lose it's accuracy. Unnecessarily high pressure also absorbs power and heats the excess oil as it's dumped over the relief valve.