Oil Pressure

[Mark H.]

I've just rebuilt my 65 SB and have very high oil pressure during the 1st hr or so of break in (over the dash board's gage of 60 psi). I was afraid of blowing the gage, so I disconnected it from the block and plugged it. I wasn't able to get a hand-held guage threaded into that no-space hole at the pick up.

Will this pressure come down ? When ? I' can't believe, contrary to my engine guy, that it is fine and that I shouldn't worry about it. I can't see driving around for the next 10 yrs with my guage pegged at 60 psi. He must a have put a hi perf pump on or something. Maybe it will come down after a few drives (its on blocks now) ?

One last question : should I be concerned with drops of oil (say 3 drops per night) coming out of my inspector plate/bell housing (right at the bottom) ? Is oil getting by the rear main seal ? Not good I would think

Thanks,
Mark

[Jack H.]

Re: Oil Pressure

Several comments:

(1) It's not uncommon for freshly rebuilt engines to exhibit high oil pressure on first start + initial driving until they've worn in and internal moving parts have seated properly. Machinests with pride tend to hold BETTER than factory original tolerances....

(2) But, when the oil gauge PEGS off-scale and stays there after initial engine warm up and doesn't drop to the high side of normal with continued run time, you might want to question the oil pump that was used.

(3) There have been several prior threads on this where folks with similar symptoms found the oil pump that was installed was either a high flow or high pressure version vs. the factory stock pump.

(4) Sometimes it's as simple as changing the pressure relief spring in the existing pump....

[Mark H.]

Re: Oil Pressure

Thanks Jack. My plan then is to leave the pick up blocked, drive for a few hundred miles, then check it again. If still too high, I'll go see the engine guy and request a new spring/pump. Not a lot a fun driving around with no pressure guage though...

Mark

[Duke W.]

Re: Oil Pressure

Why don't you ask your "engine guy" what oil pump he installed - manufacturer, part number, and specifications. Maybe it's on the parts invoice...

The correct pump is an OE replacement pump for your engine, which you didn't specify - but it must be a 300 or 350 HP if it has a 60 psi gage - not a "high volume pump" or a "high pressure pump".

The '65 327 mechanical lifter engines OE pump is "standard volume, high pressure" (55-60 psi) and those engines have an 80 psi gage.

Duke

[Mark H.]

Re: Oil Pressure

Duke,

I have the 350 HP with hyd valves, and the 60 psi guage. By your email I'm assuming you're saying that the rebuilder should change the pump out ? Bummer...

Thanks, Mark

[Duke W.]

Re: Oil Pressure

I don't know. You have to find out what's installed. If it's not a OE replacement pump then you're going to have to go argue with your "engine guy" about how to fix it and who pays.

It's common for "engine builders" to install "high volume, high pressure" pumps.

Why? The OE pump delivery volume and pressure were determined by Chevrolet Engineering and tens of millions of SBs were built with the standard volume, standard pressure pump for 30 years, and the oil system is proved to be virtually bulletproof.

If it works, why does it need to be "fixed" by some "engine builder".

I and others have been advising to use OE replacement pumps on this Board since day one, but these "too much oil pressure" threads keep popping up like a recurring bad dream.

Duke

[Anthony S.]

Re: Oil Pressure

Mark,

I was talked into a Melling high pressure pump by me engine builder & I hate it.

While I only have 400 miles on my '68 327/300 (stock rebuild) I am shooting oil out of several places, including the rear main area & distrubutor area.

I have since bought a stock pump (GM# 12555284) from my local dealer that I can't wait to install. I thought about changing the spring, but since I have to drop the pan, I might as well put the right pump in.

Good luck,

Anthony

[Mark H.]

Re: Oil Pressure

Thanks for the info Anthony - I needed to hear this. I went an saw my rebuilder yesterday on this and in fact he DID use a Melling high volume pump ("Mellings 55" I think) . So your note is very applicable. He convinced my to run it a while "the more pressure the better" (which of course is crap) and after a while the pressure would come down.... I just don't want it to come down because I blew a main seal.

I got a lot feedback supporting your experience and I'm to get the mechanic to put in the OEM pump in. Thanks again, Mark

[Duke W.]

Re: Oil Pressure

You don't have to buy the pump from GM. Replacements are made by Dana and Federal Mogul, which is what GM buys.

Any OE replacement brand like Clevite or Sealed Power is the same part. you can order a Clevite from NAPA. Just make sure it's the correct Corvette engine pump. The Corvette version of the standard volume, standard pressure pump has a pickup unique to Corvette.

Duke

[Mark H.]

Re: Oil Pressure

Thanks Duke, and all others. There's a NAPA dealer down the street, so I'll pick up the Clevite. NAPA told me he had 3 corvette pumps for the '65. Two of them are high volume, one is not (P/N 601-1057). I'll go with the later.

Mark

[Mark H.]

Re: Oil Pressure

Duke (and others),

One last question before I request my rebuilder to change out the high volume oil pump with an OEM. I've read that the by-pass valve can be removed after the oil filter is removed. Sounds easy. If so, can I modify the by-pass in some way (softer spring, if it's accessible ?) in order to reduce my pressure from its current 60+ psi to my desired 30-35 psi (recall I have the SB 350 HP, Hyd lifter motor) ? Sounds easier that dropping the pan.

If I do have to drop the pan, am I also talking about removing some of the steering assys I see below the pan ? At this point I'd like to do anything I can on my own and keep the motor out of the rebuilder's hands after his "the higher the oil pressure the better" remark.

Thanks, Mark

[Terry R.]

Re: Oil Pressure

The oil pump bypass is on the pump. The bypass under the filter is for the filter. I fought the high oil pressure problem with three different so called stock pumps finally had one modified so I could pass my PV. Look in the archives.

[Duke W.]

Re: Oil Pressure

Terry is correct. The oil system pressure relief/bypass valve is in the oil pump housing, and the difference between and OE low pressure and high pressure pump is merely the spring. You have to pull the oil pan to change it.

The valve in the filter adapter is the oil filter bypass valve. It opens at about 10 psi pressure differential to ensure that the engine gets oil even if the filter totally clogs.

High volume pumps have wider gears - the housings are phsicially larger and AFAIK they are all high pressure.

There were two OE Corvette small block pumps for '65. They are both "standard volume", but the one used for hydraulic lifter engines has a 40-45 psi spring and the mechanical lifter 327s were OE with 55-60 psi springs. Other than the relief springs the pumps are identical.

Both base and L-79 in '66 used a 40-45 psi spring, so the correct 40-45 psi pump for your '65 should be the same.

Just make sure it has the correct pickup for a Corvette, and I believe the Corvette pickup was unique to Corvette, so a 327/300 pump for a passenger car should have a different part number due to the different pickup.

The above pressure specs are for a fully warmed up engine at 2000 revs, and they are also the typical maximums at any RPM. Idle pressure will be lower, but typically no less than 20 psi.

You should be able to drop the pan after removing the two bolts that hold the idler arm to the frame on the RH side and pushing the relay rod down for adeqate clearance. This is much easier than pulling the pitman arm off the pitman shaft.

Duke

[Timothy B.]

Re: Oil Pressure

Duke ,
I have a original oil pump out of a 327/300 Impala with probably 100,000 miles. Can these pumps be used again or is it best to change to a new pump. I was thinking about checking the end play between gears and cover and wondering what other wear to look for.

[Duke W.]

Re: Oil Pressure

I reused mine at 115K. Give it a good visual inspection. If there is no obvious wear, it's okay to reuse IMO. If it never ingested a load of debris it's probably okay.

I also "blueprinted" mine by dressing down the end of the housing and one gear to reduce end play to about .002" or .003" (The spec was in How to Hot Rod SB Chevies.) and brazing the pickup to the housing.

Most engine shops replace them apriori because they don't want to take the time to disassemble and inspect.

Duke