Packard Forum Index » Post-War (1946-54)

Hello everyone. I have a question concerning oil pressure/oil sending units. The oil pressure sending unit on my '51 quit working, so I replaced it with the one listed in the parts cross reference from summit racing. The sending unit works, but now when the car is at operating temp and idling, the oil light flickers. I was concerned, so I decided to tee in an oil pressure gauge. At idle , the pressure gauge reads around 35 psi. In the service manual it states that oil pressure at normal driving speeds should be 40 psi, so I am assuming 35 psi at idle is normal. Is that correct? Can anyone chime in with thier pressure readings at idle? The sending unit I got is supposed to trigger at 20 psi, so I'm thinking maybe I just got a faulty sending unit. Any input would be appreciated. Thanks.

Even 7 psi at idle would be OK. 35 is excellent.

I think you'll find the following quote from the 1954 owner's manual, page 7, reassuring: "This (oil pressure) indicator sometimes will light up or flicker when the engine is idling even though the idle oil pressure is adequate; however the light should go out when the engine is speeded up." This happens all the time on my '54 as soon as the oil gets warmed up. Before I downloaded the owner's manual from this site I found that if I shifted the Ultramatic into neutral the light stayed out most of the time. Since I read the above statement I just let it flicker at stoplights and I haven't had any problems from this.

The factory oil pressure senders triggered the light at approximately 12-15 psi, anything over 5 psi is more than adequate at idle. See page 46 in the Engine section of the Seevice manual, "5-15 psi is satisfactory oil pressure at idle." Normal pressure at moderate speeds and above should be 40 psi. Remember, oil pressure isn't really the important thing in libricating an engine-- oil FLOW is what you need along with adequate film strength of the lubricant.

I have some doubts about whether you're actually seeing oil pressure of 35 psi at idle if the light is also flickering because of the set point for triggering the light. But if that's what you're seeing, 35 psi at idle is actually really high, and not necessarily a good thing because it could indicate your oil is too thick at startup to adequately lubricate, especially when cold. High oil pressure is also undesirable because it affects everything that depends on regulated oil pressure, so you shouldn't really ever see pressures higher than 41 psi, per the service manual.

Packard oil pumps on the straight 8s aren't usually capable of providing pressures that high at idle except momentarily after startup with thick single weight oils. It's possible you're using too heavy a grade of oil, that the relief valve in the pump is sticking, or that there's an obstruction or restriction in the oil lines.

What viscosity oil are you running?

I am running 10w-30 in it. I know that is not what is called for, but I have about 50 quarts of it laying around so that's what I've been using. I am also wondering if I am truly getting 35 psi at idle. The gauge I used is one that was laying around my dad's shop. I have no idea how old or accurate it is. I think my next step is to get a new gauge, hook it up and check again. If I truly am getting 35 psi at idle do you think that is something I should be worried about? What should I check first?

I went this morning and picked up a new gauge and hooked it up with the same results, 35 psi at idle. So I decided to take it out for a drive to see what it ran at operating speeds and also to get the motor warmed up to normal temps.
At 60mph I'm running 41-42 psi. After about a half hour drive I brought it back home and pulled in the drive at which time the oil light was on. When I put it in park the oil light flickers. The reading on the gauge at that time was 20 psi. With the car in gear it was running around 17 psi. So I'm thinking everything is good, maybe just go with a thinner oil at next oil change?

You're probably good to go. 35 psi idling right after startup isn't really a good test - until the engine is warmed up and the oil is to temperature, it's going to be thick and the pressure is going to be higher.

A few notes:
-10W-30 is the correct viscosity oil for these engines under most operating conditions and temperature ranges provided they aren't yet worn out. This oil didn't exist when your engine was originally manufactured, but if it had, that's what Packard would've recommended. In fact, after multi-weight oils had been on the market for a few years, Studebaker-Packard mentioned it in a service bulletin, and you can also reference the myriad of lube charts for your car and see that the lube manufacturers recommended 10W-30 as well.

Under no circumstances would I use an oil with a lower viscosity oil at operating temp, e.g. 5W-20.

You could, if you don't intend on driving the car in colder weather, go one step higher on viscosity. Many people on these forums (myself included) have had excellent results with mixed-fleet oils because they contain higher levels of anti-wear additives and more powerful detergents than current spec spark ignition oils. Mixed fleet oils are those intended for both diesel and gasoline engines, such as Chevron Delo 400LE, Mobil Delvac, and Shell Rotella Triple Protection. 15W-40 is a commonly used viscosity in these oils, but 10W-30 is also available in mixed-fleet brands. You can do a search of these forums to uncover a lot more information and discussion on engine oil recommendations.

-I am guessing here that you don't have an oil filter on your engine? If that's the case, pressures are going to be a few psi higher for you than many of us are seeing.

-17 psi at idle in gear is perfect, I probably wouldn't change a thing. You could, of course, be idling a little fast, in which case you'd see higher pressures than the factory spec'd. Check your idle speed once the engine is warmed up and set it to 375 rpm with the transmission in High and the parking brake on. That's a little slow for my taste, but if you want to compare your engine performance to factory specs, you need to set the engine to their recommendations. You can always go back to a slightly higher idle speed after you're done testing...

Thanks for the good info Drew. You are right about no oil filter. My car was never equipped with one. My idle speed may be set a little high also, so I may play around with that.

I can verify that my '51 288 shows around 10psi when idling hot (after a run) and around 30psi when revving (hot). This is via a gauge I fitted. The oil light never flickers, even at idle when hot. I use 10W - 30 and have an oil filter fitted also.