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post #1 of 6 Old 08-15-2013 Thread Starter
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Oil pressure sending unit

Hi all: The oil pressure switch on my Ford Lehman stared to give me eratic readings and I knew the oil pressure was fine, so I replaced the sending unit on the block with a new 0-80 lb unit. Now when I first turn the key on the gauge needle goes all the way over to 80 lbs and is pinned there before I even turn the motor over. When I do start the motor, jt goes down to 40lbs and seems to be reading correctly as that was the same reading I had before this problem all started. When I shut down the motor and turn off the key it goes back to 80 lbs and then starts to drop toward zero. When I changed out the pressure switch I also replaced the gauge, I even tried the old guage and it does the same thing. I also have a alarm for low oil pressure that is wired to a different sending unit, and that is working fine. Anybody have an idea what is going on?
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post #2 of 6 Old 08-15-2013
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Re: Oil pressure sending unit

Assuming it is an electrical gauge the sending unit probably has a variable resistor that sends current to the gauge. Although all the electrical gauges I have used read zero with the engine off maybe yours is designed to operate that way?

If your sending unit has two wires coming out of it you might try reversing them? I have never seen one with two wires, but who knows?

Paul T

Edit: Actually, IIRC, the sender sends ground to the gauge in varying amounts with battery on the other side of the gauge.

Last edited by dabnis; 08-15-2013 at 03:49 PM.
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post #3 of 6 Old 05-11-2015
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Re: Oil pressure sending unit

There are two type of oil pressure senders one that pulls the voltage to ground (that is the one you have now) as the oil pressure increases and the other is one that allows the voltage to increase as the oil pressure increases. That is the one you need.
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post #4 of 6 Old 05-11-2015
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Re: Oil pressure sending unit

Will keep an eye on this post as well, my oil prssre guage seems to be stuck at 80psi as well which is all the way over, it's a 0-80 scale.. Was working fine last season and just noticed when firing up the engine for spring commissioning.
Stays at 80 even when power off.

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post #5 of 6 Old 05-11-2015
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Re: Oil pressure sending unit

Bet gauge is toast or break in wire. Two kinds of senders (two wire).Like in old chev/ford. a broken fuel sender wire would read full or empty, depending on make.

Last edited by Capt Len; 05-11-2015 at 09:11 PM.
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post #6 of 6 Old 05-11-2015
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Re: Oil pressure sending unit

I don't know anything about boats but it sure sounds like a polarity problem to me.
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