lowest oil pressure for engine to survive 1942 Mercury engine, starts out with good oil pressure 50#, slowly decreases to about 15# as it is being driven, 20w50 oil, added some lucas extender and op went to 18# driving. Worn bearings? bad oil pump? bad relief spring? other wise runs great. no blowby. oil pressure was done with mechanical gauge
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Re: lowest oil pressure for engine to survive Not really an answer to your question but those readings are quite good for a used 33-34 motor . NO CAM BEARINGS 32-34 and that does not help oil pressure .
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Re: lowest oil pressure for engine to survive You don't say about the age or condition of the engine, or your intended usage.
If an older higher mileage motor and you're not going coast to coast those figures sound ok to me. The 59a in my truck and my crusty flatty both have similar or lower numbers than that. Mart. |
Re: lowest oil pressure for engine to survive That sounds about right for 20/50 when it warms
up. You are going to get "stories" of 3 or 4 lbs is OK but don't believe them. It takes a fair amount of oil to get a good flow into the bearings. A good flow also cools the oil when it splashes off the crank shaft. With an oil temp gauge on an open highway you can watch the oil temp go up as the engine works going up hill and cool down as it comes back down hill. Had fun watching it in my motor home on long trips. G.M. |
Re: lowest oil pressure for engine to survive I'm fighting sort of the "same" issue.......I'm running straight 40 here in Florida and this is strictly going by the pressure gauge on the car as I have not plumbed in a manual gauge at the block YET!!! SO that would be my first suggestion is to plumb a manual gauge at the block for a more confirmation and possibly accurate information. My next move is on the "next" oil change, drop the pan and maybe work the spring in the oil pump to see IF it will increase the pressure any OR possibly go to a higher pressure pump!!! Mine starts out at around 20lbs but once warm and running I get about 7ish going around 45 -50mph and "0" at idle!!! It runs spectacular!!! We have a "long time" friend who has been an engine mechanic going on 60 years now and as he told us a long time ago...."IF" its running good and has oil pressure when you are "rolling" down the road, run it till you either "have" to pull it OR until you can afford to pull it and rebuild it!!" SO following others comments and or suggestions here!!!
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Re: lowest oil pressure for engine to survive I've always heard 10 pounds per 1,000 RPM. Don't know if that's just some old wives tale or not. I do know that I had an 8ba in a '40 big truck and when it got warm it had 10 pounds or less at warm idle. Didn't have it long enough to really know how the low idle pressure affected engine life but it made me nervous looking at the gauge at warm idle.
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Re: lowest oil pressure for engine to survive are you talking at idle and hot? you should be closer to 60 on start up but its not bad, I think the main thing is when you rev you see the oil pressure go up.
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Re: lowest oil pressure for engine to survive It could be a combination of all the things you mentioned. How many miles on the motor? If this is an older or un rebuilt engine it could have run a significant number of miles with old parafin based crap oil and just have a lot of wear. If it runs quietly I wouldn't worry.
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Re: lowest oil pressure for engine to survive i used to work in a Body shop in High School, they has a 1964 Ford F350 Tow Truck with a 292, on a cold start it would have 50 lbs, after it wormed up the gauge would drop to 0 lbs. there was oil flow because it did that for a long time
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Re: lowest oil pressure for engine to survive Its best to have at least 10 pounds of pressure per 1000 RPM. Theres certainly an issue inside the engine however what on your list is causing the issue is impossible to pick. A low reading like you have will work fine around town since your not really turning very high RPM. Just go easy until the cause is determined which will mean getting inside the engine.
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Re: lowest oil pressure for engine to survive Since you get a higher reading at start relief spring is probably ok...what you lack is flow.
So either worn so flow needed is higher then pump can deliver when hot...or pump worn. A new pump may take you up to a level you can push on for a few more years... |
Re: lowest oil pressure for engine to survive there is a mechanical gauge on engine and the old electric gauge ran about the same pressure at the same time frame. think we need to pull oil pan and inspect the pump for wear and plastigauge the mains. the engine is of unknown mileage/lineage, runs smooth, does not over heat more than normal, good compression, good vacuum reading. relief spring is under intake.
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Re: lowest oil pressure for engine to survive Quote:
build a little test fixture and using a 1/2 inch electric drill and a mechanical gauge test the oil pump and relief valve to see where it dumps. Some will slowly drop and not come back up until the engine is increased. This way when you install the pump you know it works. I wouldn't put any pump in without testing first. G.M. |
Re: lowest oil pressure for engine to survive While those numbers aren't very high, my '47 has similar numbers and has been that way for years. Startup I get close to 70# but after warmed up going down the road I might get 20lbs, it drops down to about 5 at a slow idle warmed up, that's with 15w40 oil. I've driven the car from NJ to MD three times, I wouldn't hesitate to drive it anywhere. That said, at some point I plan to go through this engine.
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Re: lowest oil pressure for engine to survive GM, you are right about the oil temp, for a long time I hade one on the 33,it would get to over 100deg C on long uphill pulls , ran around 75-80C on the flat in summer here.
Lawrie |
Re: lowest oil pressure for engine to survive Hey, old Chevies of that era didn't even have any oil pressure. Strictly splash!
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Re: lowest oil pressure for engine to survive This, from Ron Bishop's book "Rebuilding The Famous Ford Flathead" - Page 51 - "Ford used 40 non-detergent oil (Summer) in all of the flathead motors. The flathead oil system ran between 10-15 pounds of pressure, but is not considered a pressurized system by today's standards."
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Re: lowest oil pressure for engine to survive Quote:
My rebuilt 258" engine with a stock Ford pump runs 55 psi at anything over 2000 RPM. My 1967 L79 Corvette 327 runs at it's factory specification as well. That specification is 45 psi. |
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