Suddenly no oil pressure reading! Thoughts

[hawghead]

I have a 1986 Wellcraft with a 350/260HP Mercruiser. Running the boat all weekend all the guages gave me good readings.

This morning I head out for a boat ride, notice no oil pressure on the guage....I had only backed out of my slip noticed the issue then pulled back in.

I have continuity in the wiring and ground. What are the odds of this being a bad gauge or sender vs. an oil pump?

THe motor sounded fine while it was running so I am not suspicious of the pump, but you never know. I have cleaned the contacts to the sender, but go no response.

Initially I had a reading of zero PSI, I fiddled around with the sender and the wiring on the back of the gauge checking ground and whether I was actuallyt getting voltage now if I start the motor the guage is almost pegged out. SO I went from a reading of zero PSI to like 80 psi at idle. Any thoughts?


ALSO,
I found this guide on another post, is all of this testing done on the back of the oil pressure gauge itself?

"Remove the wire from it,+ Ground Out the Wire,.....
The Gauge should Peg to Max........
If it Does,.... The Sending Unit is Junk......
If it Doesn't,.....
Use a jumper wire,+ Ground Out the Sender post on the Gauge,.....
It should Peg to Max,......
If it Does,.... The Wiring is Bad......
If it Doesn't,..... It's the Gauge.........

Of course,... The Gauge needs a 12V feed to it's Positive post before you start....... "

 

[Bifflefan]

Re: Suddenly no oil pressure reading! Thoughts

"Remove the wire from it,+ Ground Out the Wire,.....
The Gauge should Peg to Max........
If it Does,.... The Sending Unit is Junk......

do this at the sender.

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

The second step, just to clarify I should connect a wire from the sending post to the common ground and see what I get? Also all of this is done with the iginition on but no the engine running correct?

 

[Bifflefan]

Re: Suddenly no oil pressure reading! Thoughts

The second step, just to clarify I should connect a wire from the sending post to the common ground and see what I get? Also all of this is done with the iginition on but no the engine running correct?

Correct.

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

OK we removed the light blue to the sender and the guague fell back towards zero reattached and it pegged out. The threaded post that the light blue lead connects to was loose and wobbly. I assume that is not to 'specs'?

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

The second part of the test when we test the wiring/guage should the lead to the sender be connected or not?

I replaced the sender and then I got a constant reading of about 60 PSI at idle and while running, no change.

I did the guage test as described above, jumped the sender terminal to the ground and it pegged out. It stayed pegged out even when I disconnected the lead and started the motor. I disconnected the sender again and turned the ingnition on, then needle went to about 40 PSI which is basically 'half way' should it have go back to ZERO? I cannot get the needle to go to zero and then "show" actual reading. Usually it would read around 20 psi at idle and show greater pressure as the RPM's climbed, now it pretty much sits in one place.

I ran it for a good 7 or 8 minutes on teh water to get gas then ran back to the dock...I assume if this was actually an lack of oil pressure issue I would know by now. It runs great, just that I want the oil pressure gauge up and working so if something does go wrong I will know.

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

bump....next step to replace the gauge?

 

[oldsub86]

Re: Suddenly no oil pressure reading! Thoughts

Get or make a test guage. I have one made up of a small diameter hydraulic hose with a fitting and a guage attached at one end. Unscrew the sender and screw the other end into the spot it came out of. Fire up the engine and see if you have oil pressure. If you do the sender or some other part of your guage system is bad. If not, shut down the engine and start looking for why you have no pressure.

Randy

 

[Lyle29464]

Re: Suddenly no oil pressure reading! Thoughts

sounds like the guage. I would replace it. If you still get higher than normal readings your sender wire may be touching the block or grounding some place

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

Get or make a test guage. I have one made up of a small diameter hydraulic hose with a fitting and a guage attached at one end. Unscrew the sender and screw the other end into the spot it came out of. Fire up the engine and see if you have oil pressure. If you do the sender or some other part of your guage system is bad. If not, shut down the engine and start looking for why you have no pressure.

Randy

You mean like this...This a cheapy from Harbor Freight tools. But it seems like this should tell me what I want to know. I was already thinking that this ought to be the next step.

 

[sethjon]

Re: Suddenly no oil pressure reading! Thoughts

Hard to tell if its the sender or the pump. I doubt you have 80PSI at idle which wouldn't be bad. How old is the pump?

 

[hawghead]

Re: Suddenly no oil pressure reading! Thoughts

I do not know, I bought the boat this spring. Wouldnt the manual guage I have shown above tell me if I have pressure or not. Thus I can focus my efforts on why I am getting goofy gauge readings or no pressure at the sender. The 80 PSI isnt consistent. I disconnected the sender and turned the ignition on and the needle fell to about 40 PSI, reattached the sender and started the motor. The needle stayed at 40 PSI this time and again didnt respond to changes in engine speed (which it did before)