Oil pressure gauge at zero but oil alarm silent

badrano

Petty Officer 1st Class
Joined
Aug 7, 2018
Messages
344
Went to launch the boat off the trailer, but given this particular ramp, I have to start up the boat an move it to a slip. There is no dock where I can walk the boat off and tie up like I do at other ramps.

I started it and the oil pressure gauge read zero and flickered a couple of times to 40. After maybe 15 or so seconds, I shut it down and checked the oil and it was a tiny bit below the ADD line. I walked the boat off the trailer and tied off to a piling so that I could get the boat level. I checked oil again and it was at the ADD line. I dropped about a quart in. I started it back up and oil pressure was fine. Unless I'm having a senior moment, I checked the oil last week and it was fine. Maybe the angle of the boat/trailer last week gave me a false reading.

Thinking back about this, I remember that even though the gauge was reading zero, the alarm silenced once the engine started up. I know the alarm comes off a pressure switch, but if the alarm was not sounding, how could the gauge be reading zero?

Where is the oil pickup on the 5.0L blocks? I was surprised that even with oil at or slightly below the ADD line, there would be no pressure. Basically with the boat at the angle it was at sitting on the trailer on the ramp, there was not enough oil at the pick up??

Given the fact I had to add a quart, what is the typical oil burn on these engines? I've put over 60 hrs this season. 1 quart every 60 hrs or so??
 

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,740
The alarm and gauge use separate sensors.
The alarm might be correct and you may have a faulty gauge or pressure sensor or perhaps a loose wire.
 

badrano

Petty Officer 1st Class
Joined
Aug 7, 2018
Messages
344
The alarm and gauge use separate sensors.
The alarm might be correct and you may have a faulty gauge or pressure sensor or perhaps a loose wire.

I realize there are two different sensors. I think it's just odd that the alarm was not sounding when the gauge read zero and only after getting the boat off the trailer and adding a quart, the gauge worked as expected.

Maybe I should be adding a new sender to the winter to do list.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,417
test the sensor
check for bad connection
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Built yourself a gauge tester..

Local electronics shop. Buy a 33 ohm resistor (1/2w) and a 250 ohm rotary pot. And a couple of alligator clips. That shouldn't cost more than a few dollars.

Solder one end of the resistor to the centre terminal of the pot. Get a couple of 10" lengths of wire. Connect the clips to the end of each wire. Connect the other end of one of the wires to the free end of the resistor. Connect the free end of the other wire to one of the end terminals of the pot (doesn't really matter which one)...

Disconnect the blue wire from the back of the oil pressure gauge (from the terminal marked 'S', Sender). Clip one of the alligator clips to that terminal and the other alligator clip to a good ground. Turn the key on. As you turn the pot the gauge will move... If the gauge is good...

Chris ...

BTW. This tester will test temperature, fuel, trim and oil gauges... :D
 
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