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MG TD TF 1500 - Oil pressure

Hi All,

Can anyone tell me the acceptable oil pressure expectations of a completely rebuilt XPAG engine, at temperature, for both idle speed and "running" speed?

I've just completed this rebuild, and am suspicious of the oil pressure readings. My first thoughts were regarding the new "adjustable" pressure relief valve from Moss, and/or either a faulty gauge or collapsed oil flex line, but I don't want to start looking for trouble where there may not be any.

Thanks, as always, for any advice, suggestions, or comments.
JR Jim) Ross

Jim, my car's oil pressure ( newly overhauled engine ) reads cold: 40lbs hot 22 lbs

Hope this info is helpful,

Gerard Hengeveld

FWIW from the Operation Manual:

The oil supply is carried in the sump below the cylinder block and is drawn through a gauze internal filter and renewable external filter before circulation through the engine. It will be found on first starting the engine from cold that a high-pressure reading will be obtained on the oil gauge. This will gradually drop as the engine warms up and the oil becomes more fluid, until a normal pressure of approximately 25 to 40 lb./sq. in., (1.75 to 2.8 kg./cm.2) is indicated. Avoid racing the engine when first starting up while the oil is cold. On the other hand, do not let it idle too slowly. It should be allowed to rotate at approximately 1,000 r.p.m., an engine speed equivalent to 15 m.p.h. (24 k.p.h.) in top gear.
Christopher Couper

Jim, this is one that's well worth doing an archive check. There have been many discussions about this issue. A comfortable reading at idle is in the 20 psi area and in the 40 psi range at speed. Are you concerned that your readings are too high, or too low? There's a school that says that readings of 10 psi per 1,000 rpm are fine. Bud
Bud Krueger

Thanks to all for the info.

My concern is this:

While "bench testing this engine after the rebuild, oil pressure at about 1200 RPM, was 35 lbs.

After first starting the engine, after installing it in the car, the oil pressure was about 35 lbs. at 1,000 RPM.

Since then, having made no changes to the engine other than valve adjustment, the oil pressure is about 10 lbs. at 1,000 RPM, and about 25 lbs. at 3,000 RPM. These readings remain pretty much constant, regardless of temperature.

Having spent countless hours over the past 45 years, working on MGA and MGB engines, perhaps I'm expecting too much from this one.

I still can't understand why the drop in pressure, beginning with the second time the engine was started.

The engine starts and runs beautifully now, but I am concerned that there may just be a shoe up there waiting to fall on my head.
JR Jim) Ross

Jim, If I may suggest have another pressure meter connected to check the meter in the dash and let's go from there.

Gerard Hengeveld

Those readings don't seem bad to me with my non-rebuilt engine, But my question is, I assume you were getting an oil pressure reading on the bench from a meter attached either to the head or the block?
Did you change attachment when installing? There is a considerable pressure difference between the pressure readings obtained from those two points. My oil pressure meter in the car attaches to the head and thus got lower (but acceptable) readings of 10psi idle, 25 at 3000 rpm. Interestingly, a new oil change and filter raised those to 20/40.
Geoffrey M Baker

Pressure relief valve in the oil pump stuck open?
Lew Palmer

Thanks again to all who responded. This is why I love this site. You can ALWAYS count on getting useful, positive feedback.

I changed the oil and filter, took the new Moss Adjustable Pressure relief Valve out and cleaned it, then started the car again.

I had re-adjusted the Pressure Relief Valve to the half way position when I put it back in.

I'm unsure of what corrected the concern, but the car now has around 40lbs. at cold idle, 60lbs. at 3,000 RPM, and theses readings change downward only by about 10lbs. at temperature.

Thanks again.


JR Jim) Ross

Much better. I'm sure that you're relieved. I tend to run about 75-80 psi at warm cruising speeds and have considered the $100 adjustable valve but can really think of no reason to do it. Bud
Bud Krueger

40 to 60 psi at cruise speed in a warm engine sounds good to me. I would be worried if the pressure ran too high as I once chewed out the cam gear / oil pump gear in an engine which ran higher oil pressure. I assume the high pressure was the cause of the problem although it WAS under extra stress in a racing engine. I have seen one race prepared XPAG with an extra oil supply to these gears! An experienced engine builder who works on lots of XPAGs (e.g. Tom Lange?) might be able to say if this is a common problem. Remember that the grade of oil might also affect pressure. Isn't it amusing that some gauges (e.g. TC) are calibrated up to 160 psi!
Bob Schapel
R L Schapel

This thread was discussed between 10/06/2014 and 12/06/2014

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