oil pressure sending unit

admirals barge

Member III
1974 35 II # 325

hi all

i need a little help. my oil pressure sending unit went bad. i brought the bad unit with me to napa for a replacement. there weren't any identification markings on the old unit. the replacement unit i purchased (stwart warner)isn't the correct unit. the oil pressure gauge pegs when the engine is running. i have the original gauges and there isn't any identifcation on the gauges.

1. does anyone knows who the manufacturer of the gauges is ?
2. if you replaced the sending unit what did you purchase ?
3. if someone can take a resistence reading of the sending unit i can compare it and either put a resistor in line or a shunt across the gauge.


happy sailing



Contributing Partner
FWIW the sender needs to be matched to the guage. You may have a shorted out guage too. Examine the guage itself and test for a short internally and between the guage and the sending unit. If you can deternine the maker of the guage you may be able to match a new sender. Are you sure the sender is what went bad? If you cant match you will need to replace the guage and sender together. Any new guage should fit your panel as they are all pretty standard size 2 1/16 diameter or 52mm I believe. You may have troubel matching it in appearance with the older existing guages.


Member III
I did this on mine recently! The original gauges are PROBABLY Teleflex Marine gauges. If they have a blue-ish looking case then they probably are. I had both a bad sender and a bad gauge :(

The fact that your gauge pegs when the engine is running suggests a bad sender unit, not a bad gauge. Or a bad connection at the sender... read on:

Their site isn't the most intiutive to navigate, but I managed to find some helpful info here:


In short, you need to do this:

BE SURE NOT TO USE PIPE THREAD SEALANT - this keeps the sender unit from grounding. A common mistake... also check all connections in the event that automotive wire is used vs. marine wire... you can easily get corrosion on those and need to clean it off. Smear it in silicone or vaseline to help reduce further oxidation. Or replace with that expensive marine wire...

- 3 wires are needed:
1. Ignition to the "I" terminal
2. Sender unti to the "S" terminal
3. Ground to the "G" or center terminal

Use alligator clips and a multimeter to check the sender. With ignition on (engine doens't need to run), check the sender resistance. Should be 240 IIRC. Turn on the engine, and the resistance should lower somewhat.

Those tech docs have a "quick check" to see if the gauge works. It should bury the needle when the key is on but the engine isn't running. If the needle doesn't even budge after all that, then your gauge probably is bad.

A new one is only $26 from Boater's World. Ditto for the sender... $50 total. West Marine has them for about that much too, but BW was closer to the marina ;)
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