KingD

The 1966 327/350 4 spd is a fresh rebuild. I have it started and working on the timing, but notice the oil pressure idles at 55 pounds and runs up to 70 pounds at 2,000 RPMs. I check the oil level and it is fine. What is causing the high oil pressure?

I followed and double checked the oil pump install with oil pickup distance from the oil pan.

I am heading over the Melling site to see what they might state.

Dennis

Vet65te

Can you tell us the specific part number on the oil pump you used?
Mike T - Prescott AZ

pop23235

Did you or did you have the pick up tube brazed into the pump? If yes, did you remove the relief spring and piston first?

Powershift

Pressure is typical of a HI-PSI pump. You can probably replace the spring to bring pressure down if you really want to. My 1967 327/350 HP car oil pressure runs about the same as you posted.

However, on any new engine, after 500 miles or so, I would replace the oil and filter to get rid of any startup debris and/or start-up moly engine lube. If oil looks unusual, you can cut the filter open and also see what it tells you.

Larry

EDIT: What type of oil and oil weight are you currently running in the car??

tubman

I had the same problem. All Mellings pumps come shipped with two springs; a high pressure one installed in the pump and a medium pressure spring in an envelope. Both are incorrect; you need the standard spring which I believe is green. You should have pump number "10553". In addition to the wrong spring, my "rebuild" had a "M55HV" (high volume) pump installed, which caused all kinds of problems. I ended up purchasing the proper pump, getting the proper spring from Mellings (they were very helpful), and replacing the pump. This is not a difficult task, especially if you use the new Fel-Pro one piece pan gasket.

The Mellings high volume pump is about half the price of the proper pump, so some engine builders install it to give you a perceived upgrade and save a few bucks on the build in the process. Also be careful; Mellings also makes a standard volume pump to GM specs that has a lighter duty body casting that may break under hard usage. Plan on spending an hour or two under your car.

KingD

I believe it is a Melling M-55. I think I had two and that is the one in the box in storage. I will dig through my records and confirm. Is the M 55 correct?

KingD

The pick up was not brazed. I had to purchase the special Melling tool in order to press the pick up tube into the pump.

tbarb

If you still have the original GM pump blueprint it and reuse it along with the original 45psi relief spring.

tubman

I believe the M-55 is the one with the light duty body casting. Unless you are off-roading or doing some serious racing, it should work fine. I also agree with the above post about the original pump.

Mike67nv

When you buy a Melling M55 oil pump, it will most likely come with a green pressure relief spring installed and a yellow spring packaged with it. The green spring will give you pressures like you state. The yellow spring will drop the pressure about 15 psi, but still above the GM spec of 45 psi at 2000 RPM.

I have a Melling M55 pump in my 300HP/327 and it had a yellow spring installed. I was getting 30 psi at idle (600RPM) and 60 psi at 2000 RPM. I installed the original GM #3814903 relief spring (still available through GM dealers) in my Melling oil pump. Hot oil pressure is now 30 PSI at 600 RPM and 45 PSI at 2000 RPM with Shell Rotella T 15W-40. Right on the 2000 RPM GM spec. The spring fit fine but I did have to remove the pump to install it – the top half of the pump covered the top of the retaining pin.

Since Melling makes oil pumps for GM now, I suspect they also make the spring to GM specs. Here are pics of my M55 oil pump, the yellow (#55058) Melling spring, and the GM spring.

KingD

How long does it take to get the oil pump out, change out the springs and button everything up? I will take that time and double it because I work real slow.

Mike67nv

I really didn’t time myself but I would say it took about two hours. That’s with the car on a lift. I had dropped my oil pan three times prior chasing oil leaks, so it seemed pretty routine. You’ll need to drop the starter and the steering idler to lower the linkage. The Chassis Service Manual instructions are pretty straight forward.

Since you’re dropping the pan, it really is a great time to take care of other leaks you may have – like a rear main seal if needed.

KingD

Okay, now my head is spinning.

I went to the Melling website and here is what is written:
10553
High pressure performance upgrade for M-55 & M-55A. Standard volume oil pump. The 10553 housing and cover are CNC machined and phosphate coated. Manufactured with pink spring installed for higher pressure (M-55A). To change pump to lower pressure (M-55) install the supplied yellow spring. Includes intermediate shaft with steel guide. Built with billet steel gears. The 10553 uses a 5/8” press in screen.

I know I did not replace the spring, so I must have installed the M-55A, correct?

I do believe I installed the same pump that I have in my current inventory and this is an M-55.

So what is the difference between Melling's recommendation to install the yellow spring and the green spring recommended on this forum?

tubman

Call Mellings. They were very helpful to me and explained everything. The information on this site is pretty good, but nothing beats going right to the proper source.

KingD

I checked with the Melling customer support and they confirmed there are three springs; 78# green spring, 58# yellow spring, and a 49# green spring.

My guess is I did install a M-55A with the 78# spring.

They recommend I break it in for a few hunderds miles before tearing it down to change the spring. What damage can be caused by running at 78#?

Powershift

None. As long as the high pressure is just that………incorrect/wrong spring for your application. It could be something else such as a plugged oil filter or damaged oil pump pressure bypass. But probably not. I guess the biggest issue is your 60 psi pressure gage. Some chance of damage at 100+% of maximum scale.

Higher pressure takes more horsepower, and also puts more oil up to the rockers that has to drain back down into the pan. Only a problem if racing……….which you probably don't plan on doing.

What oil weight are you running??

As stated earlier, my 1967 327/350 HP has similar high pressures and it has only been this way since 1979.

Larry

KingD

10W30 right now. It has about a cup of moly lube used when installing the pushrods and rockers. I also put in some zinc additive as an old timer in our club recommended this.

I think I will run it for a 200 miles and then see how it performs.

I was concerned that I would blow gaskets and do other damage. Glad to see that you have been running the higher pressure with little issues.

Westlotorn

I like higher than stock oil pressure, 45-60 is good in my book and I would not sweat having 70 PSI. I would much prefer your issue to low oil pressure any day. What grade oil is in this engine? If you are running 40W drop to 30W. I am not sure how much power is wasted since the pump is already in by pass mode by 400 RPM, it would be fun to see actual numbers some day.
If you see much higher oil pressure on start up this can be an issue in Winter driving.
A cold start could bump pressure above 100 PSI and in some cases that can blow the oil filter off the block if you have a spin on filter. Normally only seen in sub zero start ups.
What was Smokey Yanucks rule, 10 PSI per 1,000 RPM. Heck your OP is good to 7,000. Rev it up.

Powershift

The solid lifter Corvettes have an 80 psig oil pressure gage as factory install, and run at these higher pressures. Both BB and SB.

For what it's worth.

Larry

donbayers

Not in 63, only 60lb