Re: what kind of oil do I use in a 1951 Packard 300

Posted by Tim Cole On 2009/5/10 13:00:20

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.