Packard Forum Index » V-8 (1955-56)

Diagnosis from afar --

Yesterday the temperature was in the 20s in Pittsburgh. I started my 55 400 which has 15W 40 Shell oil in the crankcase. The oil pressure needle pegged on high. I drove the car about three miles, the engine warmed up a bit, and the pressure fell to about 1/4 of the gage at idle. During the summer, the warm engine oil pressure is in the middle of the gage.

It will be awhile before I can investigate. Any guesses on the huge change in pressure? The engine presumably had 30,000 +/- miles on it when I bought it. The oil pan was gunked up and the piston rings stuck. Compression was so low the engine would not start.

Cleaned the oil pan, checked the mains, had the head reworked (cleaned up and valves ground)flushed out the block, installed new rings and an Aller oil pump and put it back together. No valve clatter. The car has been driven less than 50 miles since reassembly. The valves were still quiet when I discovered the oil pressure was so low yesterday.

Any thoughts on what happened? I fear that some gunk plugged an oil line temporarily, just long enough to ruin the bearings, then flushed through.

Bernardi

First thing I'd do is to connect up a bourdon-tube type (mechanical) oil pressure gauge and verify the pressures. One point of evidence that your gauge is suspect is that a cold startup should never peg the gauge, the pressure relief valve should control it to about midpoint or a bit higher on the existing gauge. Perhaps the electrical sending unit is failing.

Hi Bernardi:

If the erratic oil pressure just started with this cold start then you may have damaged something - hopefully only the sender.

The oil in your car is too heavy for winter use. What the 15W in 15W-40 means is that the cranking speed is equivalent to 15W. That doesn't mean that the oil is equivalent to 15W when cold.

The owners manual for your car specifies 20W down to 10F, so I would put 10WY-30 unless you need that heavy oil for some reason due to mechanical.

bernardi, Maybe the cold weather has something to do with the gauge readings. Unless you use the car regularly at these temperatures (lucky you as it was 0F here this morning) I would wait until more balmy weather arrives and try it again before taking on repairs which you may not require.

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.

Thanks for all the replies.

In this warmer weather, the oil pressure needle now shows a little below the middle. Apparently the sending unit was messed up with the cold. The mechanical gage shows normal pressure. I was sweating out bearing replacement, but that doesn't appear to be in the works.

Regarding the electric oil/temp gauges:

Extremely old topic but I own the same car as Reyman (original post) did, so I can chime in a bit.

On my car, the oil pressure dial in the middle of the gauge was basically 60 PSI pressure (comparing to the mechanical gauge reading from the same place) so normal oil pressure was around 3/8. Likewise, a normal temp reading from the temp gauge is about 3/8, and in cold temps more like 1/4.

I mentioned this to Ross and he said that they tend to read low. I'd like to hear others' experiences on the accuracy of these gauges.

P.S. My electric oil gauge no longer works, IDK why. Will troubleshoot in the spring.

If you put heavy stuff in the earlier cars and gun the engine on start up in extreme cold it can blow a hole in the crankcase oil regulator passages.

You always can put a bottle of 10w-30 and 15w-40 in the freezer overnight. The V-8 requires splash to the pistons. Keep in mind that the oil pump has to draw that heavy oil through a screen and if the oil starts cavitating you can get foaming that will reduce pressure which probably is what happened here given the gauge wasn't damaged apparently.

I use 10w30 and it has a 56 engine so that's what it calls out in the manual. Reyman would use 15w40 and I think his oil pressures were a tad on the high side.

Other than that, I'm not sure I follow what you're saying. Putting oil in the freezer?