High oil pressure(?)

[Gerry P.]

The oil pressure on my '57 with 283 engine is usually pegged at 60#'s. If the motor is hot, it may drop back to 45#'s at idle. I'm using 10-30 weight oil. The number on the oil pump is M55HV. The engine has approx 2000 miles since rebuilt.
Is the oil pressure excessive? I've read on this forum that a high pressure is not desirable. Is there a reason for this and would my oil pressure or oil pump "part number" be indicative of a high pressure oil pump?
Regards,
Gerry Phillips

[Doug F.]

Re: High oil pressure(?)

it's the spring in the pump that determines the pressure, sounds like yours may have the high pressure one, one of the down sides to a high pressure pump is it tends to wear out the lower bushing in your distributor,

[Stuart F.]

Re: High oil pressure(?)

I should be so lucky with my 63 L-76 using 15w-40. My gauge pegs at 80# cold and relaxes to 60# hot.

Stu fox

[Duke W.]

Re: High oil pressure(?)

You have either a high volume/high pressure pump or a standard volume/high pressure pump.

'63 SHP/FI engines used the standard volume/standard pressure (40-45 psi at 2000 hot) pump until very late in the model run when it was switched to standard volume/high pressure type (just a different relief spring) along with replacement of the 60 psi gage in the IP with an 80 psi gage, and this carried forward on mechanical lifter 327s though 1965.

Normal hot oil pressure with the above OE high pressure pump should be 55-60 psi at 2000 RPM.

We probably have another case here with this '57 283 where the "engine builder" installed an high volume/high pressure or standard volume/high pressure pump rather than the correct standard volume/standard pressure pump.

It never ends.

Duke

[Cecil L.]

Re: High oil pressure(?)

The M55HV is a high volume pump.

[Gerry P.]

Re: High oil pressure(?)

Thanks everyone for the input. Since it appears I have a high volume pump, is there a reason, other than the distributor bushing wear problem mentioned above, to swap it out for a lower volume unit. If the distributor bushing wear is the only reason, I will probably leave it as is since the car doesn't get driven much.
Gerry

[Tom L.]

Re: High oil pressure(?)

Don't forget wear n tear on the distributor gear and cam gear. As Duke continues to say, those high pressure/volume pumps can be problematic, even on race engines. Had a problem tearing up cam gears on a circle track motor years ago. Turned out to be the pump.

[Gary C.]

Re: High oil pressure(?)

Gerry, if you're going to have the car Judged it won't pass PV with that high oil pressure. Remember the 57-8 283 oil pumps are different from the later 283 oil pumps. Gary....

[Richard T.]

Re: High oil pressure(?)

Gerry your call on what to do for a car you drive little but I think your pump is incorrect for your engine. What you see on your gauge is high, about 15 PSI over on H and C. You might check the gauge to make sure the readings are correct by hooking up another gauge at the block. To high oil pressure will starve the bearings. Racing engines run high pressure pumps because the bearings have some what higher clearance for higher RPM's. Solid lifter engines use higher pressure oil pumps because these engines are built to rev higher at average of 1000 RPM's for a stock Corvette engine. I know of no excessive ware at the distributor gear or of difference distributors in solid tappet or hydraulic tappet engines build by GM for Corvettes. Maybe the gear starves for oil and will ware faster but the cam bearings are the most likely to ware out first. The pressure goes down over time with more miles driven; at 2000 miles maybe straight 20 weight would run lower pressure.

[Duke W.]

Re: High oil pressure(?)

To high oil pressure will starve the bearings. Racing engines run high pressure pumps because the bearings have some what higher clearance for higher RPM's. Solid lifter engines use higher pressure oil pumps because these engines are built to rev higher at average of 1000 RPM's for a stock Corvette engine.

High pressure will not "starve the bearings", however, too little can. Loose clearance racing small blocks traditionally need higher delivery volume to maintain the recommended 60-80 psi with sustained revs from 5000-8000. The brief time that road engines might see above 5000 does not dictate the need for higher that the standard OE 40-45 psi oil pump.

Mechanical lifter engines did not receive the 55-60 pressure relief spring until very late in the '63 model year. All prior mechanical lifter engines were the "standard" 40-45 psi. The reason for the increase has never been revealed through any surviving documentation that I know of.

Also, I know of no engine failures due to "low oil pressure" with the 40-45 psi relief springs including "light racing". Internal failures whose primary cause can be attributed to oil starvation are almost invariably the result of uncovering the pump pickup due to low oil level or high dynamic loading, and uncovering the pickup will result in an immediate oil pressure drop to near zero. A few seconds at high revs with no oil to the bearings can cause a bearing to seize, which often results in a connecting rod breaking due to excess bending load.

Though some report distributor wear issues with higher oil pressure I consider this evidence anecdotal, and not proof of any specific cause and effect. If there were any durability issues, I'm sure that Chevrolet would have addressed them.

The disadvantage of higher than OE volume/pressure involves two issues. First, higher volume and/or pressure requires more power to drive the pump and excess delivery volume, much of which is bypassed back into the pump inlet, increases oil temperatures. The second issue is primarily cosmetic, in that typical vintage Corvette engines with the standard 40-45 psi pump and 60 psi pressure gages will run with the gage pegged most of the time, and this will result in an automatic PV failure.

When mechanical lifter engines were changed to the 55-60 psi relief spring, and accompanying change swapped the 60 psi gage in the cluster for an 80 psi gage, but I already said that.

Duke

[Dale S.]

Re: High oil pressure(?)

M-55HV is the number for the Melling Chevrolet high volume SB. oil pump. Melling used to tell us at jobber meeting that the high volume had larger passages for more volume of oil, I think I remember a M-55HP for high pressure. Someone correct me if my memory fails me. Maybe I am remembering Republic Gear Co (mid 60's). I think they boxed Harry Mellings parts. I have a set of Republic motor mounts on my 67 Corvette (early 70s). I changed them just to be sure as they had a factory fix with a cable, motor to upper A arm in the mid 60's. Dale

[Duke W.]

Re: High oil pressure(?)

I don't understand this obsession with Melling oil pumps!

You can buy a Sealed Power OE replacement from NAPA, and both the various "Melling" brand part numbers and Sealed Power brand pumps are probably made at the exact same plant - just different boxes for different distribution channels.

If you order the Sealed Power OE replacement oil pump from NAPA you are going to get an OE replacement pump that has the correct flow and pressure characterisitics for you engine.

Beyond this most OE oil pumps don't need to be replaced unless they have ingested a lot of debris. A visual inspection will usually show no wear or galling, and beyond this you can "blueprint" the pump by dressing the pump housing and one gear as required to achieve .002-003" end play, and brazing the pickup to the pump housing isn't a bad idea.

Duke