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MG MGA - oil presure?

I have a 5 main 1800 engine in my A which has covered 14500 milesand runs very well, when the engine is up to temp (170 ish) and at about 2200 RPM (which is about 50mph so yes! I am a flying machine) the oil pressure shows around 45 lbs, it does increase with higher revs but does this sound about right and what is yours? Thank you, Vin
Vin Rafter

Vin

I have the same engine. Mine only ever sees about 45 lbs at idle. At all other times it sits on the plus side 60.

Steve
Steve Gyles

Vin,

Don't necessarily believe the gauge. The oil pressure on my engine improved no end after I got the gauge rebuilt.

Malcolm
Malcolm Asquith

Ditto what Steve said.
Andy Bounsall

There is a tried and true automotive "rule of thumb" that says 10 psi per 1000 rpm up to the pressure relief setting. Search on "10 psi per 1000" and you will see many articles and discussions. I've never seen that rule stated here nor would I recommend it. But it is out there for discussion. My belief is that high oil pressure at hot idle (say greater than 30) is just a waste. It actually increases wear in the oil pump, increased heat in the engine from doing all that unnecessary work, and lower performance of the engine.

The Workshop Manual states that the min oil pressure for the 1500 MGA engine is 10-25 PSI at normal running temps and idle. For the MKII, thay state 15 psi is normal at idle. Add another 15 psi for ~1500 rpm over idle and 30-40 psi at 2200 rpm seems to be within requirements.

I have just found the MGB 1800 specs: Oil pressure idle: 10 - 25 lb sq in, normal: 50 - 80 lb sq in for all models.
I assume the the 50-80 is the relief valve limit.
Chuck Schaefer

Mines a 3 bearing MGB engine Vin so it has a different bottom end ( less bearings to lose oil pressure from !) and my oil pressure is approx 20-25 psi at tickover but runs at 55 to 60psi at all other revs. 3500 miles since a rebuild so it will probably lose some oil pressure after a few more thousand miles.
I think your oil pressure is no real cause for worry if it stays in that region. IMHO, not worth investigating until its next rebuild is due, or if ever you take out the engine in the future for other reasons.

The time to look at a bottom end rebuild is when you hear the main bearings and big-ends rattle for a few seconds when you start up from cold. Its very distinctive and it means that there is not sufficient oil pressure at first to maintain the gap between bearing and journal. Then once enough oil is pumped into the bearings, the noise disappears.

Are you using 20-50 oil Vin or thinner than this?
A 10-40 oil for example may possibly not reach at as high an oil pressure as the thicker 20-50 would.

Colyn
Colyn Firth

I agree with the point on unreliable pressure gauges. It might be worth getting/borrowing a reliable gauge screwed directly into the block or oil pressure hose. At least you would get a second opinion so to speak.
J H Cole

This thread was discussed on 21/05/2010

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