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MG MGA - Help Oil Pressure

My questions pertain to oil pressure : how much (or little) is acceptable without inflicting damage to my 1600 series A engine, and what steps should I be taking to remedy this problem.

The guage reads 45lbs at start up (cold) and drops to 20 at hot idle. While driving, the guage never reads beyond 45lbs. Having sifted through the BBS archive, I understand that there probably is cause for concern, however my understanding is I am still within reasonable limits. The engine was rebuilt about 3 year ago and have since run it a total of 100 hours. I cannot say for certain what the rebuild involved. There is no perceptable knocking or other foreign noises.

I suppose the first thing to rule out is the guage...what comes next ?

Thanks for your help.

John.
John Donovan

John:

The grade oil are you using would impact the reading some. Are you using 10W30 or 20W50?

Regards,
M.D.
'57 Coupe
M. D.

good question. I can't say for certain. Would the grade make that much of a difference ?
John Donovan

Hi John. Yes, the grade of motor oil can make a significant difference. 10 W 30 is thinner than
20 W 50 particularly at higher temperatures. You should therefore run 10 W 50 motor oil in summer weather. You may find a 5 to 10 pound increase in oil pressure just by switching to thicker oil! If you drive your MG in cold weather, you may find that 20 W 50 is too thick for cold weather starting. You may need to change back to 10 W 30 for cold weather starting. Thicker oil (such as 20 W 50) in cold weather can make the engine difficult to turn over.(cranking speed is slower) Hope this helps. Glenn
Glenn

I think Glen meant to say use 20W50 in summer (he typed 10W50) and 10W30 in winter.

However, as I reread your original post, it was not clear to me whether your guage EVER reads higher than 45lbs. Right after you start the car, when the car is idling at 45lbs, does the guage read higher if you rev the engine a bit?

Regards,
M.D.
'57 coupe
M. D.

The workshop manual gives normal running oil pressure for the 1600 engine to be 50 psi maximum and 15 psi minimum so you appear to be in the ballpark. My oil pressure on start up is 60+ and then settles down to around 50 running. Idle is about 20 psi once the engine is up to temperature. I have an oil cooler fitted as well.

If you are still concerned, don't forget about the possibility of a problem with the oil pressure relief valve. It is supposed to start relieving at 50 psi on the 1600. If the spring is weak, it would relieve at a lower pressure or the valve itself may be leaking by. The problem is the location of this little ditty. It is located on the left side of the engine below the tachometer housing and just above the oil pan. There is a drain plug just above it. I am not sure that you can get a wrench on it without pulling the engine or at least removing the exhaust mainfold and everything else that might be in the way. In any event this should probably be the last thing that you try given work involved for at most a $15 part.
D. R. Carlberg

Never reads above 45. Be it while driving or revving (hot or cold). Guage ???
John Donovan

I would certainly think you'd be seeing a higher initial pressure...being a "rebuilt" engine. Is it possible the builder re-used a worn oil pump?
Perhaps the oil hasn't been changed since the rebuild...you may want to do so now. Isn't something like 30W used to help seat the rings? In any case...it has been a long time now (3 yrs), even though there's but 100 miles of run-time. At what point should the rings be considered seated?
Suggested is 10 W 30...given that winter is coming. I don't know how cold it must be to consider this lighter oil. 20 W 50 has always been my preference, but then again...I'm in CA.
Jon Bachelor

Hi Jon. Piston rings and other moving parts should be seated or "worn in" after 500 miles. When I rebuild an engine, I run it relatively gently, but increasingly harder as the 500 miles is reached. At that point, I change the low grade 30 wt "breakin oil" with a fresh lot of breakin oil. I then run the car another 500 miles, during which I push the car to faster speeds and higher revs (close to redline). After 1000 miles of gentle to hard breakin miles, I change the oil over to synthetic, and drive the car normally. M.D. Yes, I meant to say 20 W 50 in the summer, NOT 10 W 50 as I posted. Thanks for the eagle eye, and guessing my intent with accuracy! Glenn
Glenn

John:

I think that if the car idles cold at 45lbs, revving the cold engine should increase the pressure beyond 45lbs - so the guage may be faulty.

Regards,
M.D.
'57 Coupe
M. D.

John,

I would go along with testing the pressure with another gauge first after changing the oil to 20/50. Next step have a look at the pressure relief valve (as above). All this is fairly simple.

Having said that, the pressure you are getting, although on the low side, is more than I was driving on for a couple of years. I was going down to 35 at speed on a hot day and about 10 at hot idle with no knock. It worried me for a while until I had built up a spare engine and then I forgot about the pressure even when it was idling at around 5 psi one hot day.

Got the new engine in now and it runs at 60 all the time (above 1500) and idles 60 cold 45 hot.

Chris
Chris Currah

Thanks you all for your input. First things first, I will change oil and filter using 20/50. If readings persist, I will validate using a known working guage. Next step will be the relief valve. If remedy not found, I suppose I will return to the BBS for more precious advice !!! I hope I have time to get the work done before she goes into storage for the winter so I can give you all feedback. Temperature in my neck of the woods has been consistently hovering around the freezing mark for the last couple of weeks...looks as though winter is setting in early...

Thanks again !

Cheers,

John.
John Donovan

John
The MGA Workshop Manual says: "Under normal conditions the oil pressure should not drop below 30psi on the gauge at normal road speeds, whilst approx. 10psi should be shown when the engine is idling. New engines with new oil will give considerably higher readings at low speeds."

This would have been with the old recommemded S.A.E.30 Castrol XL, but it does seem pressures can be quite low. Still prefer the top end at 50/60psi though don't we!
Peter
Pete Tipping

This thread was discussed between 01/11/2004 and 03/11/2004

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