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Discussion Topic:
Oil Pressure Sending Unit - 80lb or 50lb
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scooterb84 |
02-03-2025 @ 8:42 PM
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Member
Posts: 21
Joined: Oct 2016
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Thanks Tom, your response was extremely helpful! Truly appreciate your time and help!
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TomO |
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02-03-2025 @ 11:11 AM
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Senior
Posts: 7385
Joined: Oct 2009
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To start off: the oil pressure sending unit should match the oil pump, not the gauge. If you have an 80#oil pump with a 50#gauge and sending unit, the gauge would stay pegged at the high limit on a good engine. If you have a 50# pump and sending unit with an 80# dash gauge, the gauge may seldom make it up to the half way mark. I have a 50# gauge in my car and run an 80# pump and sending unit. The gauge reads around the center portion at highway speeds. The 51 engine should have an 80# oil pump.
To answer the original question:
Your readings look pretty normal for a 20w-50 oil. If you do a lot of short trips (less than 50miles) your 30W oil may have been diluted with fuel and condensation causing sludge build up and lower oil pressure.
If you are concerned about low oil pressure, I would connect a mechanical gauge to the oil filter port to determine if my oil pressure is normal or if it is low and I may have a problem with sludge blocking the pick up screen, a failing oil pump or failing main bearings.
If the mechanical gauge shows normal oil pressure, I would check for the King-Seeley logo on the sending unit. If it is there, I would remove the sending unit and check for blockage at the port with the mechanical gauge. The King-Seeley units rarely loose their accuracy, when they do, they can be repaired and adjusted. If the King-Seeley logo is not on the cover, look for a NOS or good used one to replace yours. The aftermarket sending units do lose their accuracy after time.
I use my air compressor to provide pressure to check out the accuracy of the sending units. I connect a lantern battery and a used gauge to the sending unit and install an adapter to allow my air compressor to connect to the sending unit. I turn up the regulator on my compressor to slowly apply pressure to the sending unit and watch the readings on the gauge.
I agree with Alan on using a good multi viscosity oil in your engine. The viscosity improvers keep the oil at it best viscosity to lubricate the engine and the detergents reduce the chances of sludge build up. The valve springs in our flathead engines do not put much strain on the camshaft, so additional wear inhibitors, like ZDDP, are not necessary. Today's oil is not the stuff that came out of the ground and was supplied with little change when our cars were new. The oil companies do a lot of research on which additives to put into their oil and the effect they have on engine durability, so trying to do your own chemistry experiment with the oil in your engine could cause problems.
Tom
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scooterb84 |
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01-28-2025 @ 1:30 PM
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Joined: Oct 2016
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So I get great pressure warming up but at temp and driving it’s somewhat flat but does move with acceleration (2nd gear low RPM). Last photo is at startup and cold Middle photo is once it’s warm and left photo is very low acceleration. I have read numerous places this seems to be very normal. On a 80lb guage and only expecting 5lbs idle, this seems maybe in that neighboorhood but when driving I would think I would get the needle to move. I feel like a mechanical guage is in order to see if I get a different reading. Thoughts? Car sounds amazing and no knocking at all or leaks! I really feel like im stressing over nothing.
This message was edited by scooterb84 on 1-28-25 @ 1:59 PM
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1942deluxe |
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01-26-2025 @ 5:49 PM
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New Member
Posts: 124
Joined: Oct 2009
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scooterb84, that helps. If you change the sender, then you need the 41A-9278 80lb sender which is readily available reproduction. NOS ones appear on Ebay with some frequency. I made a special tool for that as it is quite tight in
the area the sender is located. Crossed fingers that the oil change has the desired effect.
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scooterb84 |
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01-26-2025 @ 4:02 PM
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Member
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Here is my gauge after starting cold before the oil change: I’ve yet to start it after changing oil. Been a couple rainy days in so cal and my 46 doesn’t go out to play with its wet. I’ll post an update this week after driving with the new oil. Can confirm my gauge is 80lb.
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1942deluxe |
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01-26-2025 @ 11:34 AM
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New Member
Posts: 124
Joined: Oct 2009
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Jay, I reread his post and understand now. Attached is a picture of my 46 Ford Super Deluxe oil pressure gauge.
This message was edited by 1942deluxe on 1-26-25 @ 11:35 AM
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JayChicago |
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01-26-2025 @ 10:00 AM
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Senior
Posts: 555
Joined: Jan 2016
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Original poster said his '46 has a 50lb gauge.
My understanding of that internal spring-loaded valve is it's just a high-pressure relief. Changing the spring may change the pressure upper limit, but it stays closed, has no effect, on lower oil pressures.
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1942deluxe |
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01-25-2025 @ 7:49 AM
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New Member
Posts: 124
Joined: Oct 2009
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On a 46 Ford car the dash gauge is 80lb, so the correct sender is the 41A-9278 which is also 80LB. On my 42 Ford the dash gauge is 50lb which requires the 48-9278 50lb sender. As I think previously stated you are matching the dash gauge to the sender, not the oil pump. I have a similar situation on my 46 Ford which came out of a 30-year hibernation of not being started. After putting about 40 miles on it I have 20lbs oil pressure on cold start and goes to 50lbs with revving the engine.
Actually, an improvement from where I was initially. After fully warmed up oil pressure goes almost to zero on the gauge Runs quiet with no unusual noises. I do have a NOS oil pressure relief spring and plunger that goes in the intake galley I could install. Any chance that spring could be weak? Or should I continue to drive it and keep changing the oil? Sorry about high jacking your thread.
This message was edited by 1942deluxe on 1-25-25 @ 7:50 AM
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scooterb84 |
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01-24-2025 @ 5:35 PM
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Member
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Thanks everyone. Did the oil change last night it’s been super cold here in Southern California desert. Went with Valvoline VR1 20w 50 since it has Zinc and plan to start her up this weekend and see how the pressure is. All the replies are greatly appreciated! I plan to hook up a mechanical gauge if I don’t get a reading on the gauge.
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ford38v8 |
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01-23-2025 @ 10:05 PM
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Senior
Posts: 2883
Joined: Oct 2009
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Jay, in carcrazy’s defense, he did say to get an 80 lb gauge to match the sender. I do, however, disagree with his choice of oil and additives, but only in that it’s a waste of money.
Alan
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