Oil pressure

B

billbender46@gmail.co

New member
I just had my oil pan off to replace leaky gaskets. When running my engine at idle now I see my oil pressure fluctuating from 0 to 10 lbs. Is this normal? I did not notice this phenomenon before.
 
Our 29 that we are running 20w-50 oil in starts out cold at 15 lbs. after car has been driven for a number of miles pressure is around 3-5 lbs. Summer driving.

Many years ago (1963) I removed oil pan on my than 31 Sport Coupe. When I put back on, the oil pump did not properly engage. No pressure.

There is a bolt you can install that will hold oil pump in place while you are dropping pan or reinstalling. Be careful it is a special tread.

Passenger bottom side of engine, your oil pressure line is most likely attached there.

I stand corrected. Mac’s has them. Model A Ford oil pump holding tool. $9.49. Enjoy.
 
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Please do not call it a bolt. It should be called a fitting or tool. The thread is pipe, not standard straight thread. Yes I see you also said special thread, but knowing how most people read and what they see.
 
billbender46@gmail.co said:
I just had my oil pan off to replace leaky gaskets. When running my engine at idle now I see my oil pressure fluctuating from 0 to 10 lbs. Is this normal? I did not notice this phenomenon before.
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To answer your question specifically, there is not a true pressure in a stock Model-A oiling system since the system does not have a cap to build pressure. The pump is really just a lift pump used to transfer the oil from inside the oil pan up into the valve chamber area where it will feed different areas thru gravity before falling back to the oil pan sump. My advice to you is as long as the gauge is moving, it likely is showing you that oil is being transferred. If that is the case, you are fine.
 
Contrary to some comments, there is oil pressure in a Model A engine as it is being forced up into the valve chamber. From there gravity does the work. If there were no pressure, how would a pressure gauge show a reading? Having said that, a Model A does not have a pressure oil system.

If your gauge is showing no pressure and than 10 lbs and than back to no pressure and didn’t do it prior to your removing the oil pan. Your asking a good question.

If it were my car I would check things out before running motor. The gauge could be defective, or you might really have a problem. It’s your call. It’s your engine.

I only say this because as I said earlier, I had a similar issue many years ago. Enjoy.
 
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WHN said:
Contrary to some comments, there is oil pressure in a Model A engine as it is being forced up into the valve chamber. From there gravity does the work. If there were no pressure, how would a pressure gauge show a reading? Having said that, a Model A does not have a pressure oil system.

If your gauge is showing no pressure and than 10 lbs and than back to no pressure and didn’t do it prior to your removing the oil pan. Your asking a good question.

If it were my car I would check things out before running motor. The gauge could be defective, or you might really have a problem. It’s your call. It’s your engine.

I only say this because as I said earlier, I had a similar issue many years ago. Enjoy.
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I would agree with your statement about there being some pressure, ...and I also agree with your statement that a Model-A engine does not have a pressurized system. Hence my reason for stating there is not a true pressure in the system. Thanks for clarifying that statement.
 
BRENT in 10-uh-C said:
I would agree with your statement about there being some pressure, ...and I also agree with your statement that a Model-A engine does not have a pressurized system. Hence my reason for stating there is not a true pressure in the system. Thanks for clarifying that statement.
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I’m really confused. I got an oil pressure gauge for a Model A totally forgetting it is not pressurized. I have not been able to even get oil thru the 1/8 tube and thought it was plugged but now wondering if it could even send the oil thru that smalll tube. But why would vendors sell them if they don’t work or register such small amounts. The oil pressure gauge that was originally in the car had a copper tube that was at least 1/4 inch.

Dave
 
Dave,
since the oil pump delivery of the A engine is an open system, there is no great back pressure. Only a little low pressure is created in the valve line to the oil chamber.

For this reason, standard oil pressure gauges are unsuitable for the A. You need the special low pressure gauge that can show the very low pressure. The tube diameter is not important.
 
If you have a full flow oil filter, maybe the one fitted to the valve cover, the paper element will exert enough flow resistance to show on a gauge fitted to the aforementioned ( in posts 2 and 3 above) pipe hole in the block, about 15 or 20 psi with cold oil and about 4 psi when hot. This is with 15w 50 Mobil 1 synthetic. As the cartridge element presses the bypass spring down at the higher cold reading, the gauge pressure will drop to about 10 psi at which time the spring overcomes the pressure differential and the pressure will rise to 20 again, when again the pressure differential in the filter will open the bypass. So until the oil warms and thins this pressure cycle will continue up and down in a way that reassures you your pump is working properly.
As the oil ages and becomes thinner the hot pressure falls slightly and it is time to change the oil in my opinion. That occurs at about 3500 to 4000 miles in my engines, using the above Mobil 1 oil.
My gauge reads from 0 to 20 psi and is electronic.
SAJ in NZ
 
If you have a full flow oil filter, maybe the one fitted to the valve cover, the paper element will exert enough flow resistance to show on a gauge fitted to the aforementioned ( in posts 2 and 3 above) pipe hole in the block, about 15 or 20 psi with cold oil and about 4 psi when hot.
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Thanks for that bit of info, I was wondering if or how much a full flow oil filter would affect the oil pressure in a Model A engine.
 
Werner said:
Dave,
since the oil pump delivery of the A engine is an open system, there is no great back pressure. Only a little low pressure is created in the valve line to the oil chamber.

For this reason, standard oil pressure gauges are unsuitable for the A. You need the special low pressure gauge that can show the very low pressure. The tube diameter is not important.
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Thanks for your response. I just looked closer at my gauge and it is low pressure. It goes from 0 to 10 so maybe I can get it to work.

Dave
 
Using a lube line from the oil pump gallery to the center main bearing cap along with full flow filtration actually pressurizes the center main bearing,critical for long life with a stock crankshaft.
 
That is the nature of flat heads. I had a 1948 Chris Craft with the K95 six. It was a beast of an engine. Ran great all the years I owned it. Beautiful oil pressure gauge with an 1/8 inch copper line back to the engine 8 ft from the guage. I always worried about the pressure... at best cold 5 psi. I was advised others that all the gauge is good for is initial cold start up which would show the oil pump was working. Lesson enjoy you flat head I love them !
 
Jack Shaft said:
Using a lube line from the oil pump gallery to the center main bearing cap along with full flow filtration actually pressurizes the center main bearing,critical for long life with a stock crankshaft.
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You'll likely have someone express a different view on that but I agree. It even helps with a counterweighted crank shaft. I run 25 psi to the middle main bearing on my touring engine (inserted bearings and full flow filter) which has amazed others with how well it goes and for how long it has been doing it. IMO, opinion are nice but you can't argue with reality.
 
I have not been able to even get oil thru the 1/8 tube
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I can see the low oil "pressure" of a Model A engine going through a 1/8" copper line, but I would be highly suspicious of it going through a 1/8" plastic (nylon?) line, the hole in them lines being so small.
 
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