| voced | -- 09-19-2021 @ 4:30 AM |
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I just overhauled the original LB motor in my 36 and the oil guage is not working. I put a regular gauge on it and it shows 50 to 60 lbs. So, I changed the original sending unit and still nothing on the dash. But if I ground the wire on the sending unit, it makes the gauge work great. If I use my ohm meter across the sending units out of the car two show power going through and one does not. However, none of them make the gauge move. Any idea what is going on? thanks Jerry
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| 40 Coupe | -- 09-19-2021 @ 4:47 AM |
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Appears your gauge and wiring are good. Is there a ground cable going to the engine block ? You can check by grounding the case of the sending unit to see if that makes the gauge work. If there is still no operation the sending units you have are bad. as you have done you can ground the wire on the sending unit to check gauge operation but do not leave the ground attached for very long period of time. Do make sure the sending unit is not marked "80" which is for a later engine with higher oil pressure. The sending units do have an arrow stamped on the top the arrow is supposed to point up when installed.
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| ford38v8 | -- 09-19-2021 @ 7:16 AM |
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If you had removed and replaced the sender during the overhaul, you may have re-installed it using teflon tape, which will not ground the body of the unit to the block properly. Check continuity between the unit body and the block. Alan
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| voced | -- 09-19-2021 @ 5:01 PM |
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I put an ohm meter on the sending unit at the bench and it shows going through, but when you put it on the engine it doesn't make the dash unit move with the car running. Why would it show going to ground on the bench and not make the gauge move? But if I touch a ground wire to the screw at the sending unit, it makes the dash gauge move like it should.
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| carcrazy | -- 09-19-2021 @ 8:13 PM |
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Is your car using the original 6 volt positive ground electrical system? If you have changed the system to a negative ground system, the gauge may not function correctly.
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| ford38v8 | -- 09-19-2021 @ 8:31 PM |
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That does sound like you’ve confirmed the issue I described. Put your continuity leads on the block, and the other lead on the body (not the terminal) of the sender. You should have continuity there. You of course should also show continuity through the block back to the battery. Alan
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| voced | -- 09-21-2021 @ 3:07 AM |
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Thanks guy's, I got it. Works great at almost 50lb's at idle. I think the problem was having the "up" side correct. Didn't know about that. Now my problem is, oil leak more than usual coming out of the cotter pin at the pan. I remember when I was putting the motor back together, it was hard to see how that rear main could not leak. Not sure what to do about it. Any suggestions would be appreciated.
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| carcrazy | -- 09-21-2021 @ 9:22 AM |
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Hopefully when you overhauled your engine you installed an original type 50 PSI oil pump. If you installed the later Flathead 80 PSI oil pump, you will have a massive leak past the rear main bearing when the engine is running. The early type of rear main bearing seal uses a labyrinth system which is not capable of preventing leaks with the higher pressure and volume pump. If you did use the original type of pump and still have leaks, be sure you don't overfill the crankcase with oil. Put in only the amount recommended for your engine. Also don't park the car on a hill with the rear of the car facing downhill.
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| voced | -- 09-21-2021 @ 3:51 PM |
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I know that the oil pressure idles at 48 lbs and up to 60 lbs with high RPM's. I put in the modern seal in the front , but the original in the rear. I had to cut out the splash shield in the middle of the oil pan in order to install the newer screen for the oil pump. Is there a modern rear main seal that I was not aware of. Your information is appreciated.
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| TomO | -- 09-21-2021 @ 5:06 PM |
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You can install a rope type seal for the rear main bearing, but you will have to remove the crankshaft, have the slinger ground off and try to find the pot metal holders for the seal. Your oil pressure readings suggest that you have installed the 80# oil pump. You really don't need that much pressure on the slow revving flathead, so you could go back to the long body 50# pump. The 80# pump could be the source of your leak, but the oil pump drive gear housing gasket could also be the source. Tom This message was edited by TomO on 9-22-21 @ 8:12 AM
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| voced | -- 09-22-2021 @ 1:17 PM |
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I installed the Melting M-19 standard volume oil pump. I know that this fresh rebuilt engine is going to be tight and create more pressure. And I do remember putting a new gasket on the oil pump drive gears. I did only put in 4 quarts of oil. I am going to run it a little to see if it gets better. I haven't even drove the car with the rebuilt motor yet. It runs like a clock otherwise. Thanks Tom for your suggestions.
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