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I have been reading everything I can find regarding the proper oil pressure in my '35 320 Eight engine. This engine is a fresh rebuild. At start up cold pressure goes to 55 psi, drops to 29-30 at idle when hot and has a maximum 55-60 psi at road speed hot.
Is this acceptable?
Thank You in advance
Andy

Far more than acceptable, bordering on a bit too high at maximum.

No reason to search around for information on what the oil pressure should be, it's right in the owner's manual; 25-55 psi at road speeds and at least 2 psi at hot idle.

My particular 320 engine (34) is adjusted to give a maximum of 55 which occurs at cold idle; it shows 35-50 psi at road speeds up to 45 mph, a bit lower at faster speeds, and 15-25 at hot idle. Those pressures are with single viscosity SAE 30 detergent motor oil. Your pressures are excellent, but a bit too high at the maximum. I recommend you adjust your maximum pressure to Packard's specification of 55 psi; otherwise you run a greater risk of perforating the oil cooler core or filter canister. It's the adjustment screw under the large acorn nut on the pressure regulator valve.

Packard increased the specification for 38-39 to 55-60.
Thus, I wouldn't worry given it is the same motor. I don't know what oil is in the motor, but too heavy an oil in winter can cause pressure high enough to punch a hole in the oil passages to and from the regulator.

Thank You everyone
Andy

Hi all, A number of years ago (35) I was alarmed to note that I was running Max gauge 80 psi on my 38 Super 320 engine cold using 20 W 50 oil. This decreased to 50 PSI when warm. There has been no other effects and I am happy with the Status Quo. I chimed in because it is worth noting that my adventures of over 80 psi have not been disasterous ( yet), so a little over the 60 psi should be fine. Best Regards, Peter Toet

Peter, good to hear you've been lucky so far but I'd adjust your pressure relief valve downward to 55-60 psi max. As Tim points out, rupturing the aluminum block between the oil passages is not all that uncommon an occurance with prolonged excessive pressures, as is rupturing the core of the oil cooler. And for longer engine life I'd recommend you change to a lower viscosity motor oil which will give faster flow and lubrication on startup. You have roller tappets so oil additive like ZDDP are really a non-issue.

Some old timers used to think the gauge should be pinned and those superstitions have some basis in fact for the earlier cars where the gauge pins at 40psi. Packard steadily increased the oil pressure spec during the thirties.

One thing I don't like about excessive oil pressure is that it robs horsepower (up to 10%) and generates a lot of force on the drive and timing gears. Over the long run this will create ignition problems due to slop. It also causes oil foaming which raises bearing temperature.

One case in particular I recall is a 626 where the oil pressure was pinned at 40psi. The old timer decided that he should try Castrol 50w racing oil in it. Well the oil pressure actually started to fall on the road cruising 45-55 mph. He blamed the oil and went back to 40w Wolfs Head.

In retrospect I'm sure that the car had a foaming problem and he is lucky he didn't blow the thing up.