I run 10-30w in my 194 engine. Usually when I start up, the oil pressure jumps to 10 lbs, but when the engine warms up, drops to 5-7. Now that the weather is cooler, pressure on start goes to about 15 lbs. Once in a while (1 out of 15+/-), there is 0 lbs on start. While it is at 0, there is a rap. Very soon, pressure rises to normal and rap disappears. Gauge works ok so I don't think the problem lies there. In fact, I'm not sure it is a problem. Pump? Oil distributor? Something else?

What year 194? If its a 1929-31 I would suspect the oil pump looses its prime monentarily or the oil pockets above the main bearings need to refill.
Have the pan ever been removed and cleaned?
Oil pockets cleaned?

You need a new oil pump. The pressure is too low on start-up. Also, never, ever run your engine when the oil pressure reads zero.

I would venture to say that your pump is going out. If im not mistaken, a replacement can be had at the fillin station but this is a very expensive peice. (Atleast to me) And i would not run the engine ti'll this problem is fixed or you risk burning the babbit.

Thanks for the heads up. The engine is a '32. Probably the pump is the vane type. Can those be rebuilt? I would have to say that the pan has been dropped and cleaned more or less recently, but not by me. If I buy a new gear pump from The Filling Station, I will need the pump, new pickup and screen and the pipe and fittings, right?

The vane pumps can be rebuilt but you are better off purchasing a new oil pump.

The vane pump can be rebuilt. If the pump works most of the time a good cleaning and checking of the spring(s) on the vanes is in order. The vanes need to be installed correctly and not backwards (50% chance). If there is noticeable wear to the pump body or bottom plate then replacement is best as the parts need to fit properly for the pump to function well. The vanes can be dressed relatively easily, restoring proper operation. I have never found it necessary to go to a gear pump. Have a few but never installed one. The vane pumps do a great job supplying the volume of oil required.

What are normal pressures, hot and cold, from a vane type oil pump?

For the first design factory vane pump:

Cold, at fast idle: 25 to 30
Hot, idle: 1 to 3
Hot, driving: 5 to 8

The above will vary slightly depending upon the condition of the vane pump.

If I have 30 lbs at cold start, 6-8 at hot idle and 15-20 hot driving is that an indication I probably have a gear pump? This is with 10-30 oil and a rebabbitted engine.

You might have a gear pump. However,I have found that the second design vane pump will put out pressures similar to what you describe. So, it's also possible that you could have a second design vane pump instead of a gear pump.

I agree. That what I had with a gear type pump.

I used to have this oil pressure problem and an old time mechanic suggested my detergent oil was foaming in the pump. I have been using straight 30W non detergent for the past fifteen years and have never had a repeat of that issue. Works for me, hopefully it will for you too. '29 194 ci. 30 lbs at start and 15 running down the road and 10 at idle, hot. Gary

Thats why he is called an "old time" mechanic. Actually all modern detergent oils have an anti-foaming agent.....and all oils can foam, it not the detergent that causes foaming. The non-detergent (which also means no additive package of any kind) would be more apt to foam.

When I drove out to Colorado in 2006 with my '50 I had this experiance.
While eating at a resturant somewhere in Colorado a "guy" came up to me and said. "I see your driving that od Chevy parked out there. I give you a tip. Never use detergent oil in that engine because it has those dippers on the connecting rods and that will cause the oil to foam and you will burn out a connecting rod." This is after I had crossed the great plains at 65-70 MPH (with detergent oil). I have used nothing but detergent oils in my old cars and never have had an oiling problem of any kind.

You can say that about additives, but frankly this worked for me, right away, the oil pressure issue is solved. 30W non detergent oil is readily available and I don't care if it doesn't have any stinkin' additives.
I change the oil twice a year and drive about a thousand miles or possibly less. Gary

Gary,
I can understand why you don't want to fool around seeing you had success. Would be intresting though to try a load of 10W-30 again and see if the problem is still there.\
One thing the non-detergent oil is still 100 times better than anything available in 1930.

Is read the conversation about detergent oil and non detergent. It is my experience when you have foaming is there is an air leak. Either from the shaft seal or a gasket has failed. It is the same for water pumps failing a shaft seal is worn and allowing air in. Then you have cavitations you can not pump air in a water or oil system. You can but the effects are foaming, bubbles or lack of flow. Gear pumps are less likely to cavitate as vain pumps. The fact at it was detergent oil or non –detergent may have played little in the foaming.
Definitions of Cavitate on the Web:
• Cavitation is the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation, and noninertial cavitation. ...
en.wikipedia.org/wiki/Cavitate
• A type of drag on a propeller caused by air bubbles forming near the tips of a propeller that is spinning too fast. This causes inefficiencies and unnecessary wear and tear on the propeller.
New member everett w. + have shade tree in back yard

Non-Detergent is ok i guess. You just have to drop your pan once in a great while to de-sludge it. This is something you dont have to do with a good grade detergent oil. Thats one of the reasons why detergent oil came about.