Can somebody give me some tips about oil pressure?

My 1928 M2 Rugby using a regular SAE 40 oil starts with 15 to 20 psi in the oil gauge. After running a distance of about 5 kms. oil pressure starts to drop and with less than a 10 kms. ride at medium speed (not exceeding 40 to 50 kms/hr in third shift), is in zero or close to it. Water temperature at that time is in the low level of temperature in the Boycemeter indicating cold engine far away of steam limit.

Manual says that car should be stopped immediately and so do I, when re-starting after a while all the process starts again. Oil level is OK.

Some people consulted said that it is normal and should not worry, others indicate that should add an additive or change for an oil with more viscosity, others say that the oil gear pump should be replaced or that the whole engine should be redone. Almost nobody think that the spring ball valve should be adjusted as the manual says.

Thanks in advance

Ricardo

Ricardo, You will get a lot of replies to your Oil pressure question. Most will know much more than I, however on my 28 M-2 sedan, I get about the same readings that you have obtained. I don't worry about it anymore. I stretched the spring about 3/8 inch longer and replaced the steel ball, but my readings stayed about the same. I use 20W-50 in my car. I know what the manual states, but I don't think many use the threaded cap to adjust pressure. I think most have it tightned all the way in. Perhapts some of the problem can be traced to the oil pump, but as long as the motor is running fine, I hate to get into the job of taking it apart to replace the gears. Fritz Kuenzel

Hi Ricardo. You got to have some oil pressure in our engines at all times as they are force feed lubricated type of motors. They are not cheap splash motors like in model T’s and model A’s. One thing you should be doing is running at least a 50 weight set weight oil in your engine. New the factory specified 40-weight oil. That oil back then was consistent not full of all kinds of thinning cleaners and so forth. You can even dump in one quart of 90-weight gear oil in the summer. Also if you notice the bearing tolerances back then were much bigger gaps than today. You probably need a rebuild on your engine. I run the Pennzoil set weight 50 in all my Durant and Star Continental engines. This also will quiet the engine noise down. Basically the low oil pressure is oil loss is from your worn bearings and seals. As the oil gets hot it gets thinner. It is pretty hard to wear out these type oil pumps. Hope this helps you. Later
Lance Haynes President Durant Motors Automobile Club
4672 Mt. Gaywas Dr.
San Diego, Ca. 92117
Phone 858-560-5737
Fax. 858-560-9146
E-mail: lancedurant@san.rr.com

Fritz/Lance:

Thank you very much for your advises and support.

Best regards and Merry Christmas.

Ricardo

I am no oil expert but I think I would be a little concerned about adding 90 weight gear oil to your crankcase, I have always been lead to believe that 90 weight gear oil is highly alkilinic and could cause damage to your babbit bearings, to be on the safe side check with your oil distributor, my distributor does not recommend this....As for motor oil you will get a varying difference in opinions, I use a 20-50 multi-viscosity oil in all my old cars, I think it is the best of two worlds, when the oil is cold it is equil to a 20 weight, your engine will crank better and lubercate better and as the engine warms up the viscosity increases to a 50 weight to help keep your pressure from falling back, another small advantage I found that the tappets are quiet during warm-up with the 20-50 as opposed to the fixed 50 weight...Anyway, just one more opinion...Have a great Christmas, Bill

Thank you very much Bill for your advise.

Regards and the best wishes for the new year.

Ricardo

Hi Ricardo
Wayne in Australia here,
First of all, does the engine oil pressure read high enough when cold? The oil pump and its internal wear wont vary pressure greatly between cold and hot therfore a large pressure change to me indicates a loss of supply volume.
Oil weight 20w/50 basically referes to "20w" being for cold range and 15w, 10w, and 5w a warmer range 'ie' thin oil.
20,30,40,50,60,75 referes to heavy or thick oil, hotter range.
If I had a racing car I would have a 5w/60 oil because when used in normal operation (as a race car) the oil will still have sufficient viscosity at these high working temperatures.
In the snow regions I would use 40w/20 in my car.
Now, I mentioned the word "volume", to have volume you neeed two things; oil level, and the supply of oil. You can not maintain pressure with out volume.
Many old cars {20 years plus} have sludge in their engines, the sludge sits in the stationary engine in the sump, when you start the engine the sludge is idle but as you move it becomes active and is drawn by the suction of the pump to the pick up filter which becomes blocked thus starving the pump operation of delivery volume and causes the drop of pressure.
Some one mentioned "oil flush", this is a chemical intrduced into the running engine 5 minutes prior to draining the oil.
Its purpose is to break down sludge and combustion by products in the crankcase of the engine, ie. below the pistons.
If sludge blockage is your problem, an additive and an oil change will only work temporarily. One month later the same problem will reoccure. The additive will free solid sludge which will end up mixed with new oil, and block the pump pick-up once more.
This is becoming a long reply, sorry.
If you have a blockage problem, you will need to manually remove this sludge, ie remove the sump and side covers and scrape the bulk of the sludge out of the crank case and clean the pick up strainer. After you have done this manual removal, you will still need to do regualr oil changes which should stabilize pressures.
Sorry,
Wayne down under

Thank you very much Wayne for your expert advise. I made up my mind, oil pan will be removed to inspect from below, reassuring that sucking pipe is not clogged and there is no sludge around. Spring and ball will be observed as well as oil pump and other mechanical parts. When I bought the car the previous owner said that the engine has been previously cleaned as has been idle during years and was OK. The engine was running well, but I did not have a chance to use it much since then, as other works were going on in the body. When started to drive longer runs after some miles the gauge started to show below 10 psi.
After the inspection I will put together all de wonderful advises received with a better diagnosis of state.

Best regards and Happy New Year to all my supporters.

Ricardo