All or No oil pressure

[Brimikeg]

Hey there everyone,
Just a quick question, the oil pressure on my guage either reads off the chart or none at all. I toyed with the adjustment screw on the side and it's at a point we're if I tighten it I get the off the chart reading and I I loosen it I get no oil pressure. Another thing of note is the oil pressure sending unit does not look like a factory or Moyer marine one. Could the wrong oil pressure sending unit give me incorrect readings? Or is it more likely something else. I have been working on this engine for a while, primarily fighting a stuck valve and water issues and it has had this oil pressure problem since I have had it.

[ndutton]

I wonder if maybe your sender is actually a switch, the type used for an oil pressure warning light in lieu of a gauge, a.k.a. idiot light. Can you provide a picture of the sender?

A test with a mechanical, direct read oil pressure gauge would be good information.

[jcwright]

Hello brimikeg.

Here is a link to a thread on a similar problem:

https://www.moyermarineforum.com/forums/showthread.php?t=4974

A mechanical oil pressure gauge mounted in the engine compartment is worth considering. It can help diagnose the problem, provides a check on the gauge readings you get in the cockpit, and it is handy when adjusting oil pressure.

Jack.

Edit: I see Neil answered while I was typing. I've left my post as is.

[Dave Neptune]

The above is just one of the reasons I ALWAYS use mechanical gages on a boat engine! I have water pressure so I know the water is flowing, oil pressure so I know the engine is getting oiled and fuel pressure so I know the carb is being "FED".

I will have an electric OP gage in the cockpit and a water temp gage too. I just double them up with the mechanical. However my personal practice is to never use a electric gage or fuel pump unless absolutely necessary, I don't like electricity around gasoline. IMHO.

Dave Neptune

[joe_db]

Hey there everyone,
Just a quick question, the oil pressure on my guage either reads off the chart or none at all. I toyed with the adjustment screw on the side and it's at a point we're if I tighten it I get the off the chart reading and I I loosen it I get no oil pressure. Another thing of note is the oil pressure sending unit does not look like a factory or Moyer marine one. Could the wrong oil pressure sending unit give me incorrect readings? Or is it more likely something else. I have been working on this engine for a while, primarily fighting a stuck valve and water issues and it has had this oil pressure problem since I have had it.

Get a mechanical gauge for testing. As someone else said, the sender might be a warning light sender.
Another test is to unwire the gauge and meter the resistance from the sender terminal to ground.
It should be about 240 ohms with no oil pressure and 33 ohms at full scale, which would be 80 PSI in most cases, with more or less linear variation between those points. For example, an 80 PSI sender would be about 153 ohms at 40 PSI.
A warning light sender will be 0 ohms below the warning level and infinity ohms above. Usually they open around 5 PSI.

[Sam]

Not really recommending this but it is a simple solution on my early model A4 - I have in the cockpit on my gauge panel a "mechanical" OP gauge fed by short copper tube coil tee'd into oil line prior to an inline OPS. No sending unit required. Reads about 40psi @ start up.

[Brimikeg]

This is an image of the oil pressure switch, or at least one that looks like it.

[ndutton]

Not a switch. Definitely a variable resistance sender. In no way does that suggest it's working properly though. The mechanical gauge will tell the tale.