| scooterb84 | -- 01-23-2025 @ 11:21 AM |
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Hello. Wanted to get a recommendation on which lb. oil pressure sending unit to get. I have a 46 Ford with a 51 8BA flatheaed and the oil pressure gauge in the car reads up to 50 lbs pressure but I hear a lot of people say get the 80lb sending unit on many forum posts fore my engine. If my gauge only goes to 50lb shouldnt I get the 50lb sending unit? Reason for this is my gauge as of lately has been reading somewhat normal at startup but then once it warms up falls to 0 and doesnt move much even while driving which is not normal behavior compared to months ago. I feel my sending unit may be bad and want to try and repalce to see if that rememedies the problem. Oil and filter changed recently using 30w and is at good safe level on dip stick. Ive always used 30w and never had this problem until recently. Car is running strong and no indication of any issues other than the low pressure reading. Thanks for any advice! This message was edited by scooterb84 on 1-23-25 @ 11:33 AM
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| ford38v8 | -- 01-23-2025 @ 2:25 PM |
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Scooter, your sender should match your gauge as you know, and has nothing to do with which engine you have. The fact that your gauge registers at startup and drops to zero at operating temp indicates that the sender and gauge is functioning properly, and is telling you that your choice of oil may be upgraded to help your engine and your peace of mind. A straight 30 weight oil is no longer recommended for internal combustion engines for several reasons. A good multi grade detergent oil changed regularly along with the filter should make a slight difference in your pressure, depending on that choice. You may experiment with different grades, but with the knowledge that all you need at operating temp is a slight movement off the zero mark. Alan
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| scooterb84 | -- 01-23-2025 @ 3:01 PM |
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Thanks Alan! Appreciate the reply! Flathead oil research online is literally all over the board. Years ago when I researched this 30W seemed to be the clear winner but that seems to have changed. Ive never had issue running this but if there is a better oil I am all ears. I was looking at the Lucas Oil 10w 40 which is made for older flathead engines and has high zinc. Any recommendations there? Again, thanks for the reply and your time!
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| ford38v8 | -- 01-23-2025 @ 3:46 PM |
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Scooter, Lucas 10 40 is a good choice, as are most other modern multi weights, as your question will undoubtably bring some of those recommendations. The issues to consider are: detergent VS non-detergent, viscosity, and zinc content. The use of detergent will simply require your closer monitoring of how often you change oil & filter, and will slowly improve sludge conditions in your engine. Viscosity being your initial concern, wil depend on your findings. More or less zinc will have negligible effect on a basically stock flathead engine. Edit: I meant to say the use of Detergent oil, not non- detergent oil. I made the correction above. Alan This message was edited by ford38v8 on 1-23-25 @ 9:58 PM
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| carcrazy | -- 01-23-2025 @ 5:10 PM |
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Here are my suggestions to answer your questions about what oil pressure sending unit and what oil to use in your third generation Ford Flathead V-8 engine. For maximum peace of mind use a mechanical oil pressure gauge to monitor your oil pressure under all operating conditions. Stewart Warner makes a good gauge which is available with a lighting kit and a mounting panel that you can attach to the bottom of your instrument panel. The correct Oil Pressure Sending Unit for your late Flathead V-8 which uses an 80 lb. oiling system with the higher output (80 psi) oil pump is Part Number 41A-9278 which is available from several of the vendors. You would want to also obtain an electrical 80 lb. gauge that is compatible with your sender. If you ask 100 people what oil to use, you will get 100 different answers. Here is my recommendation, use a straight SAE 30 Detergent conventional Motor Oil plus an additive which contains the proper amount of ZDDP (zinc and phosphorus). One of the oils which is suitable is Pennzoil SAE 30 API Service Rating SN or later. A suitable additive to use in conjunction with this oil is Red Line Engine Oil Break-In Additive, just follow the instruction on the label for how much to use. Hope you are able to put your oil pressure anxiety to rest. In the past I had similar concerns until I used mechanical oil pressure gauges. This message was edited by carcrazy on 1-23-25 @ 8:54 PM
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| JayChicago | -- 01-23-2025 @ 8:01 PM |
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Have to respectfully disagree with Carcrazy on which sender to use. The sender has to be matched to the GAUGE. The sender is part of the gauge. It is the control circuit for the gauge. Doesn't matter what oil pump is in the engine. For a gauge to read correctly, it has to have the sender calibrated to work with that gauge. A 50 lb gauge needs a sender calibrated to move the needle full scale at 50 psi. An 80 lb sender will give inaccurate readings on a 50 lb gauge. Thanks to professor TomO for teaching us this, on this forum, several years ago.
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| ford38v8 | -- 01-23-2025 @ 10:05 PM |
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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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| scooterb84 | -- 01-24-2025 @ 5:35 PM |
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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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| 1942deluxe | -- 01-25-2025 @ 7:49 AM |
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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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| JayChicago | -- 01-26-2025 @ 10:00 AM |
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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 | -- 01-26-2025 @ 11:34 AM |
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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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| scooterb84 | -- 01-26-2025 @ 4:02 PM |
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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 | -- 01-26-2025 @ 5:49 PM |
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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 | -- 01-28-2025 @ 1:30 PM |
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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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| TomO | -- 02-03-2025 @ 11:11 AM |
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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 | -- 02-03-2025 @ 8:42 PM |
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Thanks Tom, your response was extremely helpful! Truly appreciate your time and help!
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