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Low oil pressure

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Low oil pressure
#1
  This topic is about my 1980 MG MGB
Camper66 Avatar
Camper66 Silver Member Tyler Smith
Columbia, SC, USA   USA
1980 MG MGB
At a cold start and even 10-15 minutes into running the engine, my oil pressure is around 50-75 at idle or speed. However, after that time, at speed the oil pressure is fine, but at idle it drops to 15-20.
I am using 20W50. Of course it is really hot here in SC, so maybe my oil is thinning out a lot.
Should I be at all concerned?
Thanks.

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dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
If your idle speed is in the neighborhood of 800 rpm +/-, then 15-20 psi suggests well-worn rod and main bearings and is uncomfortably low...

Dick


In reply to # 3552510 by Camper66 At a cold start and even 10-15 minutes into running the engine, my oil pressure is around 50-75 at idle or speed. However, after that time, at speed the oil pressure is fine, but at idle it drops to 15-20.
I am using 20W50. Of course it is really hot here in SC, so maybe my oil is thinning out a lot.
Should I be at all concerned?
Thanks.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Camper66 Avatar
Camper66 Silver Member Tyler Smith
Columbia, SC, USA   USA
1980 MG MGB
That would make sense. I have over 111K on the car and to the best of my knowledge, the engine too.

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nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
The oil is thinning out, though. Do you have an oil cooler? My oil pressure went up a few pounds during the summer when I installed one on my '72.

dipstick Avatar
dipstick Kenny Snyder
La Center, Washington, USA   USA
1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie"
1970 MG MGB GT "Pat's GT"
1971 MG MGB "Gifted To Me"    & more
The low hot idle oil pressure indicates that the rod bearing shells are worn down too far. Replace the rod bearings now before the crankshaft journals are damaged. Given your 111K worn out rod bearings is very common.



Be safe out there.
Kenny

Camper66 Avatar
Camper66 Silver Member Tyler Smith
Columbia, SC, USA   USA
1980 MG MGB
Thanks for the info. I sure don't want to damage the engine.

Nick, I don't have an oil cooler. Probably wouldn't hurt in these SC summers.

Rod H. Avatar
Amity, Oregon, USA   USA
1964 MG MGB
1968 MG MGB GT
It's not a really fun job, Tyler, but doable for a DIYer, and not very expensive considering that it could postpone an expensive rebuild. Make sure and disassemble and inspect the oil pump when in there.



I can't understand why people are frightened of new ideas. I'm frightened of the old ones. John Cage

'63 MGB
'68 MGBGT
'80 VW Vanagon Kombi
'09 Mazda 3 with 5 speed manual

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nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
My experience, after changing the rod and middle main bearings, was about 15-20 lbs. more oil pressure at all RPMs. The least fun part of the job, besides lying on your back under a greasy engine for a couple of hours, is removing the oil pump gasket. Of course I didn't have a crossmember under the pan, so that made it a little easier.

What's your oil usage like? I also changed the pistons at the same time I did the bearings, because I was using a quart of oil every 100 miles. Oil usage with the new pistons is half a quart every 3000 miles.

Camper66 Avatar
Camper66 Silver Member Tyler Smith
Columbia, SC, USA   USA
1980 MG MGB
Very minimal oil usage. I rarely have to add very much between oil changes.

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dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Oil consumption is not the issue here; rather, the uncomfortably low oil pressure when hot. It all points to bearings...

Dick


In reply to # 3552972 by Camper66 Very minimal oil usage. I rarely have to add very much between oil changes.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

terryke5hwe Terry Halbert
Rogers, AR - Arkansas, USA   USA
1978 MG Midget 1500 "Midge"
1979 MG MGB "Money Pit!"
I rebuilt the oil pump along with the bearings, nice increase in pressure... The front pan bolts were a p.i.t.a!

Camper66 Avatar
Camper66 Silver Member Tyler Smith
Columbia, SC, USA   USA
1980 MG MGB
I think Nick may have been referring to the oil usage to see if more than just the bearings need to be addressed. Like the pistons.

In reply to # 3552985 by dickmoritz Oil consumption is not the issue here; rather, the uncomfortably low oil pressure when hot. It all points to bearings...

Dick


In reply to # 3552972 by Camper66 Very minimal oil usage. I rarely have to add very much between oil changes.

1st77mgb Avatar
1st77mgb Scott Mervine
Cleveland, OH, USA   USA
1977 MG MGB "Duthess"
1984 Ford Mustang "Maude"
Definitely worn bearings. Cam, crank, rod bearing are in your future.

nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
Yes, thank you. Replacing pistons is one of those things I think about whenever I have the pan off, but it's a lot of work. It sounds like your rings are fine.

In reply to # 3553022 by Camper66 I think Nick may have been referring to the oil usage to see if more than just the bearings need to be addressed. Like the pistons.

In reply to # 3552985 by dickmoritz Oil consumption is not the issue here; rather, the uncomfortably low oil pressure when hot. It all points to bearings...

Dick


In reply to # 3552972 by Camper66 Very minimal oil usage. I rarely have to add very much between oil changes.

spikerj Avatar
spikerj Josh Spiker
Provo, UT, USA   USA
1973 MG MGB MkIII "Little Red"
Definitely sounds like you need to atleast replace the rod bearings and oil pump. I just recently did the job myself, and actually restarted the engine for the first time yesterday after doing the job.

Before I took the engine apart, I was getting about 50 PSI at speed and 10 PSI at idle.

Sure enough, when I took the engine apart, the rod bearings showed some wear and the oil pump actually showed significant wear. I already threw away the rod bearings but I'll take a picture of the old oil pump.

Now that the engine has been reassembled, I'm getting 50 PSI at idle and 75 PSI at speed, so I had a very significant jump in oil pressure.


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