Re: Oil Pressure Problems

Posted by Tim Cole On 2012/7/4 11:39:09

Dear Mark:

Running one quart over is pretty much a good way to operate the Packard V-8 because it submerges the oil pump and reduces foaming.

5 psi at hot idle is pretty much okay depending on what oil you are using. Factory spec is SAE 20w, so 10w-30 is a good choice for a new motor. For an old motor people like 15w-40 which is fine and has more detergency because it is for diesel trucks. Keep in mind too that on modern cars the gauges are computer controlled to minimize customer complaints, the gauges are just decorations. My modern car has lights for everything except temperature and I'd just as soon prefer a hot/cold light for that as well. As long as the MIL is off I really don't care what is going on under the hood. It doesn't have a tach either and I don't care.

Now on to this DeSoto question. If memory serves me correctly it was dropping to 20 psi at 35-45 mph which is low. On a V-8 you can't isolate cam bearings as a cause of low oil pressure, but on flat head inline motors there are plugs in the side of the motor for the camshaft oil holes. In the old days used car dealers used to cure low oil pressure by putting restrictors inside those plugs, and viola!, good oil pressure. Low oil pressure in the absense of motor noise is symptomatic of worn cam bearings. When mains are bad oil pressure is low too, but there is also some motor noise, less so in V-8s but very much so in under square inline motors like Packards.

Oh, and the rule of thumb for required oil pressure is 10 psi per 1000 rpm. So for a worn motor with 30 psi oil pressure at 50 mph the maximum rpm you want to operate at is 3000 so a car like that should be fine on secondary roads but will blow up on the highway. In the old days I remember cases where someone would buy so and so's original Packard and promptly blow it up on the highway whereas as the original owner did very well driving it around town.