Oil pressure gauge problems
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Tuned
Joined: Jun 2017
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Oil pressure gauge problems
The oil pressure gauge on my 1978 4.9L/300 isn't budging at warm or cold temps. I just replaced the sending unit (twice, to be sure) and still no change. I can ground out the wire and when I turn the key on, the gauge pegs out at high, so everything seems ok from the wire to the dash. I changed the oil and filter recently with 6 quarts of 10W30 and it's usually at or below 32 degrees for me currently.
What are the odds my oil pump needs to be replaced? Short of getting a mechanical gauge, is there anything that can be done to troubleshoot?
What are the odds my oil pump needs to be replaced? Short of getting a mechanical gauge, is there anything that can be done to troubleshoot?
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Sounds like the gauge itself is OK. If the pump failed for some reason, you'd know about it right away.
I looked for a mechanical pressure gauge for a while after replacing oil pump on my slick. Kind of wanted a vintage SW type, but I didn't want to wrap up $100+ for the gauge & running it up to the dash, copper line, T fittings etc etc. I found an old school 0-100 psi large face with steel braided hose and a passle of fittings for $10, works great for testing.
BUT, they sell "oil pressure test gauge" (in a genuine DeLuxe plastic blo-molded case) and fittings and the rest of it for under $20 delivered to your door. That would be one way to go, or rent one maybe. Hot oil pressure @ 2000 RPM is usually spec'd in the manuals, 35-55psi, something like that.
I looked for a mechanical pressure gauge for a while after replacing oil pump on my slick. Kind of wanted a vintage SW type, but I didn't want to wrap up $100+ for the gauge & running it up to the dash, copper line, T fittings etc etc. I found an old school 0-100 psi large face with steel braided hose and a passle of fittings for $10, works great for testing.
BUT, they sell "oil pressure test gauge" (in a genuine DeLuxe plastic blo-molded case) and fittings and the rest of it for under $20 delivered to your door. That would be one way to go, or rent one maybe. Hot oil pressure @ 2000 RPM is usually spec'd in the manuals, 35-55psi, something like that.
Fleet Mechanic
Joined: Dec 2007
Posts: 1,505
Likes: 339
From: Wildwood Pa
The parts store could be giving you the sender for a dash light, rather than a sender for a gauge. Some parts jockeys are not too bright, & some parts locator computers are not too bright when it comes to older vehicles.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Could be right! The gauge senders are quite a bit larger in size than the idiot light senders. Good point. Guess that's why you make the big bucks.
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Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
Myriad 1957/90's FoMoCo vehicles.
This is a large dome shaped sending unit. The "idiot light" sender is much smaller and is not dome shaped.
See 9278 in lower pic for large dome shaped sender // Upper pic shows the idiot light sender.
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Tuned
Joined: Jun 2017
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I dig the enthusiasm! Friday night is movie night here, so the truck had to wait.
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Tuned
Joined: Jun 2017
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Pretty sure I've got the right part. It's BWD S334 and says it's for the gauge, not the light. But I've been wrong before on parts! The sender is just a little smaller than a tennis ball, for what it's worth.
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Tuned
Joined: Jun 2017
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Update: Well, she's just about warm and the mechanical gauge is sitting at 55. 
Still puzzled about the dash gauge. My best guess, at this point, is that my connector is wacky. I accidentally stripped it during the rebuild and after looking at it closely, I might be missing a strand or two in the bundle. Not sure that would be enough to cause a problem because the circuit is ok from the wire to the dash and the sender unit tests ok for continuity, so.... 
Still puzzled about the dash gauge. My best guess, at this point, is that my connector is wacky. I accidentally stripped it during the rebuild and after looking at it closely, I might be missing a strand or two in the bundle. Not sure that would be enough to cause a problem because the circuit is ok from the wire to the dash and the sender unit tests ok for continuity, so....
Lead Driver
Joined: Jul 2017
Posts: 9,597
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From: San Jose, CA
He mentioned 10w/30 and that seems reasonable I think?
But what about that sender test finding zero ohms? Where did you test it? The units themselves have a range from 73ohms (empty) to 10ohms (full) so a test should never result in zero ohms.
This is between the tip where the wire connects and the body (or threads) where it's grounded through the engine.
Sound correct? If so, find out why you have no resistance when testing the unit. Seems that with three new units all reading the same on the gauge, it's unlikely they're at fault. But stranger things have happened!
What about the original? When did this low reading start?
Paul
But what about that sender test finding zero ohms? Where did you test it? The units themselves have a range from 73ohms (empty) to 10ohms (full) so a test should never result in zero ohms.
This is between the tip where the wire connects and the body (or threads) where it's grounded through the engine.
Sound correct? If so, find out why you have no resistance when testing the unit. Seems that with three new units all reading the same on the gauge, it's unlikely they're at fault. But stranger things have happened!
What about the original? When did this low reading start?
Paul
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Tuned
Joined: Jun 2017
Posts: 356
Likes: 2
He mentioned 10w/30 and that seems reasonable I think?
But what about that sender test finding zero ohms? Where did you test it? The units themselves have a range from 73ohms (empty) to 10ohms (full) so a test should never result in zero ohms.
This is between the tip where the wire connects and the body (or threads) where it's grounded through the engine.
Sound correct? If so, find out why you have no resistance when testing the unit. Seems that with three new units all reading the same on the gauge, it's unlikely they're at fault. But stranger things have happened!
What about the original? When did this low reading start?
Paul
But what about that sender test finding zero ohms? Where did you test it? The units themselves have a range from 73ohms (empty) to 10ohms (full) so a test should never result in zero ohms.
This is between the tip where the wire connects and the body (or threads) where it's grounded through the engine.
Sound correct? If so, find out why you have no resistance when testing the unit. Seems that with three new units all reading the same on the gauge, it's unlikely they're at fault. But stranger things have happened!
What about the original? When did this low reading start?
Paul
Cargo Master
Joined: Jul 2005
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From: Kansas
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