Packard Forum Index » Pre-War (1899-1942)

BDC, Excellent idea. Thanks for the tip. I 'll start doing it as well
Tom

G'day Tom and others,

This recent article on Hemmings may or may not lead to the views you need, you just never know.

I just went and checked it out and it looks like a possible source, for sure. It isn't cheap, but probably cheaper than wasted time, mistakes or inaction ! I'll give it a try and let everyone know.

Thanks for the lead !
Tom

It took a while but here's a photo of the oil pressure relief valve assembly.

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A that's what I was looking at alright...Thank you for digging it up !
How do I know whether it is working properly or if it needs adjusting ?

Given the right combination of conditions (engine clearances, oil viscosity and temperature, engine speed) the oil pump on your engine can produce oil pressures that are harmful, possible damage includes perforation of the oil filter, the oil cooler heat exchanger, fracture of the main bearing oil manifold, and even rupture of an oil gallery in the cast aluminum crankcase. To prevent this possibility the oil pump output is passed thru a pressure regulator (relief valve) to keep the maximum pressure within acceptable limits (55-60 psi maximum). The regulator is simply a piston within a bore, loaded against a spring whose tension is adjustable by the screw located underneath the large acorn nut on the relief valve. If the pressure overcomes the tension of the spring, the piston moves to uncover a passage whereby a portion of the flow is dumped back into the crankcase, thus reducing the pressure.

Remember, the valve adjustment sets a "not to exceed" pressure. Highest pressure normally occurs with a cold engine on start-up, and with increased engine speed. If under these conditions your gauge shows more than 60 psi you should adjust by loosening the adjusting screw, thus lessening the spring pressure on the piston.

Normal pressures vary a bit over the life of that engine but are typically at least 3 psi at hot idle, and 35 or more psi at road speed with the correct viscosity oil for the ambient temperatures (see owner's manual). If your pressures are much less than this, it could be from just a worn and tired engine but also could be from either a broken or mis-adjusted relief valve. If by increasing the spring tension adjustment (tightening the screw) your pressures increase, the valve is incorrectly adjusted - continue adjusting until your max pressure (cold engine, high engine speed) is regulated to the 55-60 psi max. Problems with the relief valve itself are pretty much unheard of but you can remove the valve assembly itself to inspect and make sure the piston moves freely and the spring is unbroken. You don't remove the entire unit from the engine block, just the valve assembly unit accessed beneath the large acorn nut.

My oil pressure per dash gage usually reads 30 at warm idle, a little higher till warm, and 45-50 +/- at warm speeds of about between 25 to 50-55 MPH.

OD, I can't thank you enough for taking the time to provide this in-depth explanation. It will be printed out become an important part of my growing reference guide and my on-going education. To the best of my knowledge there is no place else to get this type of quality information if not from people like yourself willing to take the time to impart what you've learned over the years to the uninitiated like myself. Thanks to you and all who share.
Best regards,
TomB

Excellent oil pressure, about the same as my '34 has; about 25-30 psi at hot idle and 40-45 at road speeds with SAE 30 detergent oil. I have my max pressure set to 55 psi as years back when I allowed it to go higher I split an oil filter open at the seams.

I would not consider any adjustments.

OD, What's your opinion on SAE 40 W non detergent (i.e. Rotella T) with a Lucas additive ?
I can't/wont argue with 50 years experience, just interested if my current usage/advise is detrimental or "just as good" ?
Thanks.

First of all, if my engine was clean inside I'd use a detergent oil and if it wasn't or I didn't know, I'd drop the pan and clean it and the pump intake screen thoroughly and then use a detergent oil. Unless you will see a lot of really hot weather service, SAE 40 is a bit high, lighter oils moving and larger volumes probably provide better longevity. As you have a roller tappet engine, additives above and beyond what is already in a good grade of oil is unnecessary though probably not harmful though I'm sure you've read that excessive concentrations of additives like ZDDP can actually cause an inversion and be harmful. My 34 seldom seems use in temperatures above 85? F so I use major brand SAE 30 detergent, CAM 2 or Formula Shell; no snake oils or additives.

Rotella T is NOT a non-detergent oil. And I wouldn't add any additives to an already additive-rich oil like Rotella T for the reason mentioned above.