To much oil pressure

[Lawrence S.]

I just had my 67 L79 rebuilt and it runs great, sounds great, but I have to much oil pressure in my opinion. When I fist start it up under fast idle the oil pressure gauge is pegged past 60 pounds. When the oil finally gets hot it pretty much stays at 60 pounds while cruising. I read that 45 pounds is where the gauge should be at 2000 rpms.
I am contemplating removing the oil pan and changing out the pump that the builder put in there. I have a faint oil leak now that looks like it is coming from around the rear main seal. The motor has approximately 400 miles on it since it has been rebuilt. Should I put more miles on it and see if it gets better or try and nip a problem in the bud before it gets worse?

Thanks,

[Stephen L.]

Re: To much oil pressure

If you plan on having it judged or PV'ed you'll get knocked for high oil pressure. I have the same problem without the leak.....

[Lawrence S.]

Re: To much oil pressure

Just had it flight judged in Charlotte---Second Flight.
It was the White Car/white top with Blue and White interior---(with the shiney paint!)

[Mike M.]

Re: To much oil pressure

see if the engine rebuiler has the weaker oil pump spring and install it. its a simple proceedure once the pan and pump are removed. mike

[Duke W.]

Re: To much oil pressure

Find out the manufacturer and model number of the installed pump from your "engine builder".

There are three basic types of SB pumps:

1. Standard volume, standard pressure 40-45 psi @2000 hot
2. Standard volume, high pressure 55-60 psi @ 2000 hot
3. High volunme, high pressure, 60 psi or more @ 2000 hot

The only difference between 1 and 2 is the relief spring, which is easy to change.

Type 3 will pump excess volume for a road engine even with a "low pressure" spring. The excess oil is bypassed by the valve back into the inlet the but high volume requires more power to turn the pump and this parasitic power heats up the oil and reduces power at the flywheel.

Oil pumps are simple devices and are easy to disassemble and inspect. If the gears are not worn or damaged, I see no reason not to reuse the pump, and it can be "blueprinted" as advised in various "how to" books on SB rebuilding.

If you do have to replace the pump, install a standard OE replacement Federal Mogul pump, not some hot rod pump. Buy the correct pump for your engine. The number for '64-'65 mechanical lifter engines should be different as this is a 55-60 psi pump. It is also applicable to late '63 mechanical lifter engines that have 80 psi gages.

All other 327s use the standard pressure pump.

For those of you who turn restoration of your engine over to an "engine builder" insist on only OE equivalent parts from Federal Mogul or Dana - brands like Perfect Circle, Sealed Power, Felpro, and Victor Reinz. Agree on a list of brands and part numbers. Online catalogs are available to assist you. Don't let them install "low compression" pistons unless you want to use regular unleaded fuel and are willing to take a 10 percent hit on the torque curve across the range.

Have the compression ratio MANAGED to achieve a target range based on calculations using measured deck clearance, published or measured piston and head chamber volume, and then select a head gasket to acheive the target. Maximums that I recommend for TRUE, MEASURED, CR are 9.75:1 for 300 HP, 10.25 for Duntov and L-79 cam engines, and 10.5 with the 30-30 or LT-1 cams. These limiting values can usually be meet with OE replacement pistons on OE machined blocks and heads with judicious head gasket selection.

If the guy wants to fill up your engine with aftermarket hot rod brand parts go elsewhere. I've seen to many engine restorations get screwed up by "engine builders". They end up with low compression, too much oil pressure, and cams that aren't like OE - usually too much overlap, and these combinations produce poorer than OE idle quality, poorer than OE low end torque, and no more than OE top end power.

That's called getting nothing for something - not a good deal.

Duke

[Joe L.]

Re: To much oil pressure

Lawrence-----

1) Remove oil pan;

2) Remove oil pump;

3) Remove oil pump cover with attached oil pump pickup;

4) Measure the length of the gears. If it's 1.2", you have the correct, standard volume pump. If it's 1.5", you have a high volume pump. In that case, replace the pump with a standard volume pump. A Melling M-55 will do just fine. If you want to use GM, use GM #12555284;

5) If you have the correct pump as far as volume is concerned, remove the oil pump pressure relief spring in the cover. It's very easy to do this. Just remove the small pin and the spring should pop out. Install new spring GM #3814903;

6) Re-install oil pump cover;

7) Re-install oil pump, properly torquing the retaining bolt to 65 lb/ft;

Re-install oil pan;

9) Done.

[Ray G.]

Re: Same readings w/ a master gauge? *NM*

[Lawrence S.]

Re: To much oil pressure

Guys,

Thanks for the responses.

I will let you know what I find out.

[John M.]

Re: To much oil pressure

Duke, Joe,
I have the same problem with a 427 engine. I'm chasing an oil leak which I believe is the rear main seal or the contact area at the rear main. This engine pegs the oil pressure gage even when hot. Since I'm taking the pan off I think I should change the oil pump spring or the oil pump alltogether. Is there a simple way to tell if it's the GM part as in Lawremce's L79?
Thanks.
John McRae

[Duke W.]

Re: To much oil pressure

Changing the spring to OE should do the trick even if it's a not-OE pump. Hopefully Joe can help you ID it.

Duke

[Joe L.]

Re: To much oil pressure

John-----

Older GM pumps will usually have "GM" cast on the cover or on the body of the pump. Newer GM pumps are outsourced and may or may not have the "GM" trademark on the pump. A 6, 7 or 8 digit GM part number found on the pump is also a clue to its being a GM piece. However, if there is such a number, there will almost always be a "GM" seen, too.

Unless you find a metal tag on one of the cover bolts with a GM part number on it, none of the other numbers found embossed on the cover or the pump will be the part number for the pump assembly.

[Loren L.]

What weight oil is in the engine? *NM*

[Jeff Bukowski]

Re: To much oil pressure

I have the same situation with a Melling pump ( as do others). The standard volume and pressure pump in my 67 327/300 oils at 55 lbs warm at 2000 RPM, and around 70lbs when cold with 15-40 oil.
I had another engine with a GM pump that oiled at 45lbs at 2000 RPM hot (50 lbs cold) and 30 lbs at idle. When I replaced that pump with a Melling 55(long story) the pressures jumped to what you are seeing.

If you replace the standard Melling with a new one, you'll get the same pressures.

My engine now has around 1500 miles with no changes in pressure. There are shops that can correct your pump so maybe others can help out with names. I've decided to leave mine as is.

[Joe L.]

Re: To much oil pressure

Jeff-----

Did you try replacing the pressure relief spring in the Melling pump to the GM spring that I mentioned? The only reason that I can figure that the Melling pump would deliver such a high pressure is that the spring used has too high of a tension rating. As far as I know, the GM spring will work in a Melling pump.

[John H.]

Re: To much oil pressure

If you're buying a new Melling pump (or a GM pump made by Melling - same part), you DO NOT WANT the new "lightweight casting" pump shown in the photo below, identifiable by the "ribs" in the casting; GM redesigned the pump casting in the last 18 months or so, and there are lots of reports of pump casting failures surfacing under high-rpm/heavy-duty use. There's more info on the Melling site and from the Melling tech guys - go with the "old" design without the ribs, which has always been bulletproof.