How to adjust an DC Oil Pressure Gague

[sjcare]

1982 Cheerman Trawler, twin Ford Lehmans. I replaced all the gauges last summer on the lower helm. I noticed the port engine oil pressure seemed to be reading a little high. So I mounted a mechanical oil and water temp in the engine room for both engines so I always had a source of truth.

The port engine lower helm oil pressure gauge reads about 20lbs higher than it should. Is there anyway to adjust the gauge or sender? It would be nice to have them all dialed in so I can trust them.

For reference the gauge is: Sierra 80180P Marine Boat Heavy Duty 2" Oil Pressure Gauge 0-80 PSI 12V Teleflex

 

[RT Firefly]

Greetings,
Mr. sj. What make are the old gauges? In some cases, you must change upper and lower and the sending units as a package.

 

[sjcare]

Greetings,
Mr. sj. What make are the old gauges? In some cases, you must change upper and lower and the sending units as a package.

I did actually replace the upper helm gauge so it matched. So the sender and the gauge match.

 

[CharlieO.]

Have you swapped the gauges around to verify the problem is in the gauge?

 

[STB]

This is most often caused by corrosion at one of the terminals or an intermediate connection. Senders are resistors and added resistance along the way changes what the gauge sees just the same.

I'd start by seeing what resistance you measure at the sender by itself, with both gauges disconnected at the sender, and then again at the top by each gauge with only one sender wire connected at a time. The measurements at the gauges are the critical ones. A difference there points to a problem. The other one is just a quick way to verify the sender.

Some senders have two different take terminals, one for each gauge. I'd still follow this procedure, even though disconnecting is less important with that setup.

You can Google and find a curve for your senders, either by sender or gauge model.

If you can find one, post photos or numbers and I'll look and see what I have.

 

[sjcare]

Ok,

Will do, thanks for the detailed explanation. I will post the findings when done.

 

[C lectric]

First thing I would do is CHECK THE CONNECTIONS for any sign of corrosion.

All of them.

{A quick and dirty check would be to bypass the wiring between the sensor and the guage. NOt to be pretty so it can be run across the floors, through hatches and so on. If the guage readings improve then you KNOW the wiring connections are the problem.}

Do not just look at them. Even minor oxidation can cause changes in the readings. These things are resistive devices and any additional resistance will cause reading changes.

I re-terminated many of my guages and it made a difference. My shunt type ammeter simply did not work. I re-terminated all of the connections and away it went, working. I simply cut off the old crimp on fittings and replaced them.

A tip. Some of the wires and contact pads showed oxidation. I lightly coated those wire ends with ROSIN flux and heated them, soldering iron only, so the ROSIN was active. It cleaned off the strands.
THen alcohol cleaned the ROSIN remainder off and installed the new terminals.

An eraser used on the contact pads will likely help as they are slightly abrasive.

This last step may not be needed but watch for any sign of corrosion in which case it may be.

All screw terminals were cleaned and then I used No-Alox paste to lightly coat the contact pads and screws to SLOW further corrosion.

Your boat you say is 1982. THe odds are good that unless you rewired the whole system that one or two connections are oxidized, corroded, wire terminals poorly crimped or loose.

If you are not SURE about the connections/wiring then a new guage or any other work will likely be non productive.

Happy hunting.

 

[Jc180]

A quick look at the Sierra spec sheet, does not appear adjustable. The dual helm pressure sender is one variable resistor resulting in theoretically the same resistance signal to each of the two gauges. So since the upper helm is reading correctly, can consider the sender, the upper gauge circuit, and the upper gauge good. That leaves the lower circuit and lower gauge. As others have said, bad connections can change the circuit resistance and effect the gauge reading. Or could be a bad lower gauge. They are not precision instruments, but that error is too large.

 

[RT Firefly]

Greetings,
Mr. Jc. OR a mismatched lower gauge that IS functioning properly BUT of the wrong internal resistance.


I had a bad oil pressure gauge that was no longer available. I had to change both upper and lower gauges AND the (dual) sending unit to achieve proper readings.

 

[Comodave]

As suggested above the different ways to troubleshoot this is, swap gauges and see if the problem follows the gauge. If it doesn’t follow the gauge then I would run a temporary wire from the sender to the gauge to see if it works that way, if it does then you have a bad wire or bad connection. Then if it works with the temporary wire you can either troubleshoot the wiring or just run a new wire permanently. That may be easier than looking for the bad wire or connection, depends on your boat and access to the current wiring.

 

[Itwasntme]

If you eliminate the corrosion issues, then you can put a resistor of the proper value in line.
First, with a mechanical gauge of known accuracy, note the pressure displayed for a number of points of RPM.
Then wire in a variable resistor and adjust it until the pressure displayed lines up most accurately with the results you got with the mechanical gauge.
measure the ohms on the variable resistor and buy resistors that match that value, and install them

 

[catalinajack]

1982 Cheerman Trawler, twin Ford Lehmans. I replaced all the gauges last summer on the lower helm. I noticed the port engine oil pressure seemed to be reading a little high. So I mounted a mechanical oil and water temp in the engine room for both engines so I always had a source of truth.



The port engine lower helm oil pressure gauge reads about 20lbs higher than it should. Is there anyway to adjust the gauge or sender? It would be nice to have them all dialed in so I can trust them.



For reference the gauge is: Sierra 80180P Marine Boat Heavy Duty 2" Oil Pressure Gauge 0-80 PSI 12V Teleflex

Are your senders matched to your gauges? Are your gauges dual station? If so, you must use a dual station sender.