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Looking for some help. I purchased a 1940 110 project car about five months ago and have been working on it since. The engine was stuck from sitting but no visible damage to the cylinders. I did all the basic stuff including dropping the oil pan, replaced the head gasket, rebuilt the brakes, generator, starter etc…My question is this. I removed the oil pump, cleaned it and reinstalled it. Oil pressure at a cold start was always 25 to 28 psi. At warm idle it would drop to about 20psi (SAE 30 weight oil). I realize pressure is low but what makes no sense to me is that lately driving the vehicle around the block a few times pressure drops considerably and does not return to 25 to 28 psi for the next cold start. It appears as though under load with acceleration the oil pressure does not increase but instead drops. I installed a mechanical gauge and have seen it drop to 4 to 6 psi under load. I’m wondering if there could be a problem with the pump or could I have made a mistake with it during reassembly. I also think I probably have a stuck ring because the car is burning oil and has a misfire in cylinder #6. It starts right up though and runs pretty smooth. I plan to pull the head again and go after the rings. Before doing that I figured I should confirm the oil pump is working properly. Any suggestions would be greatly appreciated.

You may have a problem with the oil pressure limiter, which I think is built into the oil pump body. That's the first thing I'd check.

The fit of oil pump parts is critical, and gaskets of the wrong thickness might cause excess clearance and low oil pressure.

A problem with the oil pump suction screen assembly, such as a leak in the pickup tube, could cause low or erratic oil pressure.

A badly worn engine will have low oil pressure. Such engines usually exhibit excess mechanical noises and excess crankcase blowby, especially when warmed up.

Oil burning that is limited to one cylinder may be a broken ring, but it could also be stuck rings or a clogged oil ring. An ignition problem affecting one cylinder can mimic an oil control problem.

Any condition that allows excess oil to accumulate in the valve guide area may cause oil burning. That problem is more common in overhead valve engines, but it can affect any engine.

Another thing to check is the fuel pump. If it is the type that has a vacuum booster built into it to assist the windshield wipers, a bad vacuum diaphragfm can allow crankcase oil to be sucked into the intake manifold. This could cause cause fouling of one or more spark plugs. It would not affect oil pressure. Also, be sure the fuel pump is not leaking gasoline into the crankcase. That could cause low oil pressure. Your crankcasae oil should not smell like gasoline.

Thank you TxGoat for the detailed response. By oil pressure limiter are you referring to the pressure relief spring? I opened the nut on the pump housing / pressure relief valve and the spring came out along with a metal sleeve. Not sure if the sleeve should be pressed into the housing. It basically fell out with the spring.

I think I do have a hint of gasoline or combustion odor in the oil. I figured it might be the result of a worn, stuck or broken ring but never gave thought to the fuel pump. I don’t have a vacuum hose attached to the fuel pump so probably not a vacuum assist for the wipers. The pump is mounted to the engine directly above the oil pan. Can the pump leak fuel into the engine?

G'day Joe,
to PackardInfo.

Don't mean to (oil) pressure you but I invite you to include your '40 110 Touring Sedan in PackardInfo's Packard Vehicle Registry.

Very cute, Mal! You're on a roll with the invitations!

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Yes, it can if fuel gets through a torn diaphragm that is still able to pump a little, it will go right into the crankcase.

You said, I believe, that the engine was stuck when you got it? What steps did you take to un-stick it and after doing so, did you check and/or hone the cylinders and replace the rings at the very least? If not, you shouldn't have been running it at all until those things were done.

No telling how "loose" the motor is. I run Rotella 15-40 oil in my 327 motor which helped tremendously with blowby. Also a quart of Lucas Oil stabilizer and a long drive really helped to free up the stuck rings on my long slumbering engine.

The oil pump springs can be shimmed to increase spring pressure and increase oil pressure.

On my engine I'd say hot oil pressure at idle after a long run is around 10psi.

I had once a 47 Dodge with one wiped main bearing. The oil pressure was just OK when coasting or under light load, but dropped many pounds under load as the crank moved over to one side and really let the oil out.

The oil pump on your car is likely ok as they seldom give any troubles. More likely your engine will need its bearings checked. Any funny noises?

The engine cylinders only needed a little Mavel Mystery Oil. Only a very light surface rust. They freed up easily however the output shaft on the transmission was seized to the crank. I had to remove the transmission and replace the pilot bearing. Had many things going on so figured I would put it back together to see if I had compression or rod knock before going any further. I knew I was rolling the dice but this car was making my head spin. It started right up and continues to do so. Was hoping to drive a little and get a feel for the car but the oil pressure isn't good while under load.

I'm thinking I may have the same issue here. The only unusual noise is what I describe as a warble type of sound as the engine runs. Almost sounds like suction. Thought maybe it was the crank stirring oil in the crankcase but only a guess. Wish I could post a video with sound.

Hi thank you. I will definitely add it to the registry.