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I have a 1951 Packard 300 and the manuel says to use
20 weight oil, where can I get it. I can get 5-20 oil
from Walmart. Can anybody help me with this.
Thanks Roger

Use 10W30 or 10W40. The factory would have recommended them if they had been available at the time.

I'd avoid SAE10W-40 and would absolutely avoid SAE5W-20. 10-30 should be fine as Rusty suggests, and many folks prefer to use SAE15W-40 intended for trucks and light diesels as it contains a somewhat better anti-wear package of additives. Whether it's really better is debateably, kind of "might help, can't hurt".

Roger: If you haven't dropped the oil pan and cleaned it, then I would use straight 30 weight NON DETERGENT oil of some name brand.


John F. Shireman

I recommend Classic Car Motor Oil. It is a multi-viscosity 15W40. It is a specially formulated with 1600 ppm ZDDP. The API service category is SH, SJ, SL. It is for older flat tappet engines for which the new oils are not compatiable. It is sold through the Indiana Region of the Classic Car Club of America. To order phone: 317-225-0040 or go to www.classiccarmotoroil.com. I am using it in my 1937 Six and 1947 Custom Clipper.

Hi Roger:

Pulling and cleaning the oil pan is sound advice and also is part of Packard scheduled maintenance. Once a year in 1948 (I don't have a '51 manual handy).

If the motor is heavily sludged then detergent motor oil will simply use up all the additives real fast and become like dirty oil. However, good non-detergent motor oils are hard to find. Castrol has a full line of ND for which they claim is state of the art sans detergent, but I'll be darned if I can get a hold of it. Most other ND is just not very suitable for Packard motors unless is it changed every 500 miles.

Packard didn't like heavy motor oils because they run hotter and strain the oil pump. Single grade detergent motor oils are generally recommended as being heavy duty and intended for severe usage like trailering.
Again Castrol has a full line of these that may be available through NAPA.

The heaviest I would run is 10w-30 although I would prefer what the book says 20w. These multi-grades can run heavier or thinner base stocks.

The most important thing here is to change the oil regularly as the manual says and avoid short period running.

I'm not sold on these heavy multi-grade oils because this zinc stuff is directly opposed to what the petroleum engineers say about SM rated oils. I think these problems are likely the result of neglected oil changes and dirty oil pans.

Good luck.

Thanks to all that helped me with my choice of oil.
You were all a big help! At this time, I have decided
to go with 10w-30. I have not done anything with the oil
pan.
Roger

A couple of thoughts-

10W30, multigrade, detergent oils were just coming on the market when your car was built. Chances are, all it has ever had was 10W30 during its working life because that was the "default choice" of all dealerships and garages for most of the last 50 to 60 years.

In recent years oil companies have cut down the anti wear additives especially zinc. This is OK for late model overhead cam engines but not so good for older pushrod engines. The lack of antiwear additives can cause rapid cam and lifter wear in pushrod engines because of the weight of the valve mechanism.

Your flathead engine has a light weight valve train like an OHC engine so the ordinary oil should be fine. If you are at all concerned, diesel rated oil still has the full additive package. The diesel oil you usually find at your local stores and gas stations is 15W40.

Hi Roger

I checked some figures on these oils and 5w-30 actually comes closest to 20w in terms of viscosity at running temperature. So in a rebuilt motor I would use 5w-30 providing the oil pump is new or rebuilt.

These diesel oils are 1/3 thicker at running temperature than 30w which is probably helping to raise the oil pressure in worn out pumps. If the oil pump is shot then heavy oil is not harmful. Obviously, if oil pressure at 35 mph is well below spec than something has to be done to prevent rod bearing failure.

Packard only authorized heavier oils for temperatures over 100F and to control oil consumption. If the motor has excessive blow-by then piston lubrication will be reduced and wear accelerated. Too heavy an oil will cause starvation below operating temperatures. 15w-40 isn't that much heavier than 30w at lower temperatures and so using it old motors is not a crime.

One thing that is important here is that heavier oils reduce settlement rates. These are very important without full flow filtration. So lighter oils run cooler and cleaner than heavy oils. That's good for any motor.