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

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 .

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!!!

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.

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.

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.

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

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.

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.

Re: lowest oil pressure for engine to survive
 

Look up a couple posts I did a few years ago that describe how to
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.

Re: lowest oil pressure for engine to survive
 

Would that be the one you did with the "plastic tube" and "100psi Gauge"???

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!

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."

Re: lowest oil pressure for engine to survive
 

I find this to be an amazing statement and quite hard to take seriously. I think I have Bishop's book (I bought every flathead book I could ever find) and have not looked at it in years. I guess this helps explain why.

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.

Re: lowest oil pressure for engine to survive
 

The ol' 'Lucky Dip'.:rolleyes:

Re: lowest oil pressure for engine to survive
 

I run a 286 CI 8-BA with 20-50 oil. Runs about 50 psi at start up but when hot about 10 psi at idle. Have not had any problems in 10 years or more. I've been told that it isn't about oil pressure with a flathead it's about flow. Just my experience and I run it hard.

Re: lowest oil pressure for engine to survive
 

Old chevies of that area had 14 lbs. to the mains and to get oil up to the rockers.
The rods had dippers that were dipping into puddles that were full and running over with oil.
My dad had an old Oliver 70 farm tractor with a Continental 6 cylinder ohv engine.
The shop manual said, “remove the little oil galley plug and with the engine running the oil should barley trickle out. We worked hell out of that tractor and it never did quit and never showed any oil pressure. But those are different engines. Our V8s need at least 20 lbs. at speed
I’d drop the pan and check or replace the inserts. I’d also install an 80 lb. oil pump.
These engines are getting scarce.
Aaron Griffey
Hayward, CA

Re: lowest oil pressure for engine to survive
 

anything above 0 to quote Bruce Lancaster. 50 hot is interesting. 5-10 hot is not out of normal and good.


Flatheads are not a high pressure oiling system. model A four bangers where just a oil delivery system.


If it's stockish... All that high pressure does nothing. Well it washes bearings. Relax it's all good.

Re: lowest oil pressure for engine to survive
 

Pressure and flow is what you need to get sorted out...as long as you have flow you usually get away with it.
With the exact same reading on a pressure gauge you can have very different scenarios...
You can have a good oilpump that is able to put out flow with a worn engine...it will run until the knocking and rattling scares the heck out of you no issues.
But the other way around a poor oilpump in fair engine will end up bad fast...
So just saying as long as you have a little pressure all is fine is a course diagnose.

Re: lowest oil pressure for engine to survive
 

A gauge is a gauge it reads whatever. If you have a worn engine and a bad oil pump, well no flow or pressure.... If you have pressure you have some flow. Bearings help to create pressure... if the pump is bad as well... 0 is bad. But without pressure you have no flow.



Saying flatheads need more oil pressure then "we think they do". High pressure oil pumps are neat but not necessary. Hot oil pressure at a reading of 5-10 lbs is not a rebuild or bad motor scenario. It's just stock normal hot oil pressure.

Re: lowest oil pressure for engine to survive
 

well we changed out the relief spring under the intake to NOS and also added a 1/4 washer this helped with the initial oil pressure but about the same running down the road, think we need to rebuild another engine--not sure a new op would help but at the cost of a gasket we might try. I do have a few used pumps ,including some 80 lb pumps, if I did this should we block off the reief spring under the intake or what?

Re: lowest oil pressure for engine to survive
 

What you just said makes sense. The 80 or 50 lb is a maximum. When warm, running down the road or at idle you are nowhere near the blow off pressure of the valve, so beefing it up makes no difference.

Personally I'd leave both valves in place so the oil feed to the timing chain area is regulated properly. But that's just me and I've never had to do it.

Re: lowest oil pressure for engine to survive
 

If it has the original pump putting in a 80 lb pump raises the flow so it will be able to maintain pressure better when hot.
The relief valve in the gallery should be left in place it serves dual purposes.

Re: lowest oil pressure for engine to survive
 

I usually use a piece of 1/4" pipe 3/8" thick for a spacer. If it also
has a valve in the pump the valve with the weakest spring will
determine the pressure. G.M.

Re: lowest oil pressure for engine to survive
 

GM how did that 3/8" spacer affect the oil pressure?

Re: lowest oil pressure for engine to survive
 

If you really want to know where your oil pressure goes use a pressure pot of oil to pressurize the oil gallerys before you put the pan on, then look where the leaks are, the bearings should drip, any missing plugs will make a big leak, and a steady stream out a bearing probably means too much clearance or a defect

I had to fix a Mercedes engine that the owner said had no oil pressure showing on the dash,that the gauge must be bad, it had 3 lbs at 2000 rpm on external gauge, it had been driven a month that way, I found 1/2 a bolt on top of the oil filter, upon removal of the pan 1/2 of the oil pump housing laying in the bottom,a windage tray bolt had been sucked in, no bearing damage, just a new oil pump

Re: lowest oil pressure for engine to survive
 

So 80 to 50lb is normal, hot or cold...... hmmm

Re: lowest oil pressure for engine to survive
 

NO...…...80 or 50 lbs. MAXIMUM is normal, hot or cold. ALL words matter! DD

Re: lowest oil pressure for engine to survive
 

Is the hydrodynamic principle fulfilled?once that occurs oil pressure doesn't matter..model a engines relied on 3 inches of gravity to satisfy the bearing demand.

https://i.imgur.com/1yVa48j.jpg?1

.001 bearing clearance per inch of journal diameter,,10 inch diameter battleship crankshaft? .010 bearing clearance..any oil pressure beyond whats needed cools and cleans the bearing,but isn't necessary for function

Re: lowest oil pressure for engine to survive
 

It's a unicorn. Most flatheads are low pressure oil. It's not right to say a motor at 10lbs hot is a goner. I have a tight rebuilt that runs 50 at start and hot idle at 20. It's a good rebuild and no I didn't put a high pressure oil pump in it.

Re: lowest oil pressure for engine to survive
 

Are you kidding me? Factory specs say 55 lbs at 2000 RPM and 25 psi at hot idle. My engines meet these specifications. I can't help it if you have a bunch of worn out boilers.

I thought one of the the purposes of this forum was to promote quality builds. I hope I'm not wrong.

Re: lowest oil pressure for engine to survive
 

Tub you first to get at me. In a perfect world you will be the first to put another motor in it. Sure you can tell me how to convert to 12 volt too.

Flatheads will always be a low pressure system. 10-20 at hot idle is normal.

Re: lowest oil pressure for engine to survive
 

You are right. Share your rebuild. I've shared a couple rebuilds here and on the yblock forum. Have at it.

Re: lowest oil pressure for engine to survive
 

It was done by a guy named "Dave" who runs the machine shop at the NAPA in Baxter. He told me that he had never done a flathead, but had worked for a Ford implement dealer and had done a bunch of 8N's and 9N's. That was all I needed to hear. Everything went great (and it didn't break the bank, either).

Re: lowest oil pressure for engine to survive
 

Ya stop telling me how it is, show me.