Technical High flathead oil pressure

Gents, this is my first flathead, so I'm still figuring certain things out. So forgive the stupid questions from time time.

Is there such thing as too much oil pressure on a flattie? Mine idles around 25 after warm up, and traditionally ran around 45 cruising. I tuned it up a few weeks ago and changed the oil (Rotella 15-40), and now everything is the same, other than at highway cruising the oil pressure gets up to 60-65.

Am I good to go or wat?

Thanks guys.

 

Were you running the same oil brand/viscosity before the oil change?

The typical oil pressure rule of thumb is 10 psi per 1000 rpm. 60 - 65 is a little high, I don't know that it will hurt anything, but I'm not a flathead guy, so maybe there's something peculiar about that engine; but typically higher oil pressure than needed is due to high volume pump, possibly particulates or varnish/sludge causing sticking of the oil pressure relief valve, which could be bad if the valve sticks in the open position and you lose pressure. I'm a little concerned on why the sudden jump in pressure.

 

I would change to a 10W30 to lower the pressure which is on the high side. What is your cruise rpm?

 

Drive it down the hi-way about 50 miles on a 90 degree day and check back in with us.

 

That's kind of what I was getting at when I asked about what oil he was using before. He's located in Michigan, and I ***ume it's pretty cold up there this time of year, and a 10W-30 probably would be a better viscosity recommendation. But I'm still wondering what oil he was using prior to the recent oil change.

 

I don't know what oil was in it previously, first change since I've owned it. (I chose that oil based on opinions in threads on here from flathead guys)

It was 65 degrees yesterday.

I'll take it for a spin this weekend and see what she's feelin and report back....

 

I don't know the flow paths in a flathead lube system, but the basic thing to remember is: pressure is the RESISTANCE to flow. Are you trying to push too much oil through p***ages and clearances (high volume pump)? Is the oil viscosity too high? As stated above, try a 10W30. Did you ***emble this engine? If so, how were the clearances in cam and crank bearings? Also as asked above: what rpm are you turning at 60-65 mph?
Are you using a mechanical or electric gauge/sending unit? If electric, do they match electrically? If mechanical, try adding an auxiliary gauge to double check your existing gauge.
Find any 'shiny stuff ' in drained oil? What temp is it (both engine temp and ambient) when you are recording these pressures?

 

Sorry, I'm a slow typist, so I repeated/missed some posts while I was doing the one-finger dance on my keyboard!

 

Oil Filter ? Modern Oil filters some have a rubber flap to prevent oil draining out of the filter.
One time I put one on my Flathead Banger that usually idles at 2lbs and is 10 psi at speed, with the modern flow flap filter it had 25 lbs at speed and ruptured my old Rex-A-Co 12 lb pressure gauge.

 

Normal filter. No metal in the last oil change. I didn't build the motor, no. Electric gauge, I was thinking of checking it on a gauge. Engine runs great right now, at a rock solid 180 degrees. 60ish degrees here all last week, and the car lives in a heated garage, so it's always warm.

Did some reading on the barn and some flathead guys there don't seem scared by that number.

That's really my question, is this even a problem? I'll take her for a spin asap and note the tach/press.

 

First of all, it sounds like your engine is in pretty good shape (at least the bearings). It's really not a good idea to run heavier oil than needed as it makes the oil pump work harder and generates heat. At this point in time, I would go back to 10-30 automotive oil and see what happens. I would be willing to bet it will be just fine. I'll do a little editorializing here and say that there is no benefit in using oil with an additive package designed for diesel truck use in a spark ignition engine in an automobile, and it may even be detrimental.

There may be a problem with the relief spring in the oil pump being a little too stiff, but I don't think the difference (10 psi) is a good enough reason to tear the engine down to check and/or replace it. I would expect a flathead in good condition to idle at 25 psi and run at 55 psi, so you're still in the ball park and I don't think you have a problem.

Someone in the past probably shimmed or stretched the spring to achieve just such a result, which also is not a good idea.

 

I'm just getting ready for another oil change soon, so I'll follow that advice. The motor has 2000 miles on it since rebuild, only about 600 of those are me. The guy I bought it from built it, and hardly ever drove it. I believe it was built in like 2006? Ish? He had 4-5 cars and used this kind of like a show queen. So I think she's still getting used to how often I drive her....

 

If I remember correctly there is a spring and a ball that goes inThe block in the. Valley right front corner I think on 8ba’s that was for oil pressure. Check that . If I didn’t remember correctly someone will soon straighten me out.

 

Well I drove it today real quick. Ran great. About 35-40 pounds at idle, and sits at a rock solid 60 at speed, pretty much any speed. Rpm at 50-60mph is about 1700-2000.

Im thinking it's the new oil as well. I'll change it and see what that does.

 

Many and I mean many use Rotella in non Diesel applications. This includes motorcycles...It' s got a stout additve package for Diesel or gas..
I have changed viscosity like the OP and after a good run to warm the oil the engine had about 5 psi more pressure...

 

Just a question, seems you didn’t ask what type of oil the PO used. All good, but when you went to change it, did it flow out good?
Or take it’s time?
I just changed the kids oil the other day in an OT car, uses 0-20, damn it went fast and quick. My OT DD I run 10
-30 and can tell the difference when I pull the plug.

 

During the war we could get drain oil for 3 cents a quart. We let it sit a week to let the black gook settle out and then ran it till it was gone. Never pulled the pan plug till VJ day. Never lost an engine because of oil or lack of it.

 

I still don't see a problem. Lippy

 

I can't ever remember changing the oil cause it had too much oil pressure!

 

I believe the Motors manual list 50-55 psi as normal for an 8BA at rpm,,,cruising .
So,,,,sounds like the engine is good inside .
I would suspect the oil myself,,,,these engines don’t need a very high viscosity if the bearing clearance is good .
Don’t sweat it,,,,,,I think the engine is fine .

Tommy

 

I run an 8ba and use 15-40 Rotella, no filter, year round and I drive it year round in New England. I change the oil once a month. My oil pressure ranges between 45-55. I like a mechanical guage better myself but whatever it doesnt matter.
I'm no expert but I think your fine

 

I like 5W30 Mobil 1. I use it on everything even the lawn mower lol... I always thought 15-40 was diesel oil...

 

It is. Ive used Mobil 1 for years also.

 

The early flathead blocks 1932 to 1948 have that check valve ***embly. The latter 8BA style block dose not.

 

There's absolutely nothing wrong with those oil pressure readings. As others have written when you get into really warm weather you will see a drop in your readings. I decided to add to this post not based off of theory but true real world experience for a very long time now.
Ronnieroadster

 

Hey 210,
Don’t think anything of it,,,,your pressure is fine,,,Ronnie knows what he is talking about .
So,,,,you can always lower back the viscosity on your next change,,if need be .
At least you have a sound engine,,,that is comforting to know .
Sometimes you read about people that have bought hot rods with freshly rebuilt flat heads and they realize they only have about 20 pounds at speed and less than 10 at idle .
Which doesn’t speak well for the rebuild or the clearances inside .
I know that these engines can run on that low of pressure,,,,,however,,,,after a fresh rebuild,,,that cost thousands of dollars,,,,,no way in my book .
An old engine yes,,,,,fresh rebuild,,,no !
Maybe that’s just my way of thinking,,,,,but,,,,,I believe that is what these engines are capable of .
If built right ,,,,,they can last past our lifetimes.
Yes,,,,,,you must change the oil,,,,and,,,,,you must keep antifreeze in them.
Keep them tuned up,,,,and don’t overheat them .
The rest is natural .
Good going,,,sounds like you have a good one .

Tommy

 

When I bought the car, I took a quick tour of the seller's shop and other cars. I started the car and said I'll take it. He said don't you wanna dig around it a bit? I said no and just handed him the envelope of cash and drove away. I saw his level of work and organization. I could see the 4 link, and under the hood was impeccable. I knew he built it right. He said "you won't be sorry", and I haven't been.

Thanks for all the pearls gentlemen.

 

Andy was a Hotrodder back in the dayz

 

Quick update: for whatever insane reason, it seems to hold steady at 20-45 again, depending on rpm. Hasn't p***ed 50 once since I posted. Weather has been similar, but I've been driving it a lot, and it just seems to have settled back down. Weird.

 

If pressure is holding steady I don’t think you have a engine problem .
So it must have been the pressure relief valve,,,,or a bad gauge .
Either way,,,,sounds like the engine is good and tight inside,,,clearance wise.

Tommy