flathead oil psi?

I got a 50 Ford with a stock flatty that's been a daily driver since late spring.
After a tune up and fluid change it kept 30psi oil pressure when driving along.
Now, when driving along the oil psi will drop to 25/20 psi. But, if I get outta the gas it pop back up to 30 psi and then slowly drop down again.
It never runs hot(or that's what the temp gauge says).
Dip stick says the oil level is good.
The weather has been warmer here lately. Was in the 70's now in the upper 80's. I wouldn't think that would have anything to do with it, but you never know.
Do you think this is a problem? And if so, what?
Or, should I be happy the 58 year motor ticks along just fine and stop worrying about it?

 

Be happy, cam bearing get worn and pressure drops. Lot of old flatties will do good to have 5lbs. at idle. I and many others run 20W-50.

 

+1 on the 20W-50 suggestion. You're fine though above 20 psi. My old 8BA ran 25 - 30 and would fluctuate too.

-Lee
Atomic Radio
www.atomicpinup.com

 

Don't worry, be happy. No need to get into overhaul type issues til something seriously ceases to function. If you really need a hard, filthy job, drop the pan, shovel it out, remove and clean the pickup screen. You can even remove intake at same time and do about a 90% cleanout of the engine...but you and your garage will have to be discarded as beyond cleaning afterwards.
Anti-sludge tech for later developement: PCV setup (easy on a '50) and 180 thermostats.

 

Thanks guys!
It's my first running flathead, and i kinda want to keep it that way.
Cory

 

I am trying to think of a reason for the oil pressure to rise when the throttle is closed.

Still can't think of a reason!!
Vacumn in the pan? Not likely, no route to pan from intake,
Less pressure in pan, due to less blowby?
Cam moves forward , closing oil holes a little? Perhaps!

whatcha think?

traderjack

 

My guess... worn main bearings (and maybe rod bearings.) Under load it probably keeps the crank on the main caps, alleviating pressure at the mains... And off throttle, it pushes up more toward the block... increasing pressure.

Alec.

 

You got it^^^^but sort of normal. A worn SBC does this too.

 

That fluctuating is from thrust surface wear, IMO. I hate to say it but I had a '53 F-100 that started doing that, and within a couple thousand miles it threw a rod. It might well be worth dropping the pan to see if throwing a new set of shells and pump in is worth it, before it gets worse.

 

You need to specify what weight oil you used in your oil change. Multi viscosity weights like 10w-30 give you odd oil pressure readings and may be the sign of fluctuating oil pressure gauge readings. Even as good as the new lubricants are Non detergent 30W seems to work best in a flat motor for everyday use.

 

Dick, I've got a great deal of respect for you, but it surprises me to no end to see anyone recommend non-detergent oil in this day & age.

Are you recommending it because it may have been run w/o detergent oil in the past & you're concerned for sludge breakdown?

As to the specific problem, I can't say why it's doing what it's doing other than guess, so I won't. I would run a quality 20W50.

 

It was 30w shell oil.
It's funny, everything I own is breaking all at once.
Both the transmission went out on my '51 pickup and the steering in my 2000 pickup developed a strange shimmy last week.
Happens in threes I guess.

 

Here is something weird. I have had my little hemi running for 20 years. I decided to get some insurance and put in so Rotella diesel oil. I assumed nothing would change. The engine is smoother and the idle speed increased??

 

Ernie, Sometimes people don't tell us the entire scenario of their issue, therefore responses are more of an "in general" nature. A good running used engine and a new rebuilt looks a lot different when opened up. Unless the life story of a flathead engine is known, you can pretty much bank on the fact that its sludged up so, I wouldn't be recommending long term use of detergent oils in a used engine unless you are doing frequent oil changes. The new oils are tricky because many are synthetic based, the actual viscosity index rating becomes a factor that can vary by brand. Even oils with the same W grade, can give a slightly lower reading when hot.

Right now I've got a fresh rebuild flathead with Gibbs oil in it. I'm not against new products, I'm assuming this is just a good running old engine and my take on the situation. In this case the engine has 30w so my guess is that the pressure is a little lower because the operating temp when up a little but it can be as simple as different brand of oil. Part failure or severe wear usually shows up in more drastic fluctuations.

 

My hot oil pressure went up when I switched to a diesel oil in my flathead...don't know about smoothness or idle speed on mine, but oil pressure (on both gauges - I have stock & aftermarket) went up hot about 5psi - and I went from 20W50 to 10W40 too!