Re: Oil Pressure

Posted by BH On 2008/3/1 16:18:18

bernardi -

Gauges used in these Packards were such that the needle pointing straight up indicated normal operating condition. That was a brilliant, yet subtle, design feature that provides for great at-a-glance recognition - since the driver should keep his eyes on the road as much as possible. Today's vehicles (and their engineers) aren't nearly so accomodating.

That said, a gauge reading of only 1/4 of the sweep doesn't sound too alarming, but I agree that you need to install direct-reading gauge to watch for and help analyze any emerging issues.

I doubt that the use of 15W40 oil is a factor at these temperatures. I believe you'll find several Packard owners here who have had no problem using it - especially in the V8s.

The whole idea of multi-viscosity oil is to have the oil flow well on a cold start up, to minimze the cold dry running time (and cold wear), yet have sufficient viscosity to prevent wear when the engine is fully-warmed up. That is accomplished by viscosity-improving additives.

Now, I'm no petroleum engineer, but it's my understanding that such additives do NOT thin the oil when cold, but actually thicken the oil at higher temperatures. So, 15W-40 oil is SAE 15 viscosity at cold temps, but thickens up to SAE 40 at full operating temperature. While there are other additives that keep oil from getting thick in extremely low temps, I believe they are only combined with oils meant for use in artic climates.

However, these helpful viscosity-improving additives do break down with use (namely from high temperatures), and there comes a point where the oil becomes too thin at normal operating temps to provide sufficient protection against wear - even causes sludge to form. Yet, I suspect that most of us change our oil more than often enough in these fine old cars.