NSF18b2 oil light issues

Gopz

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Oct 10, 2020
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Greetings. I am at lost with this motor 2003 nissan 18hp fourstroke
I am having this issue on the oil pressure
I have replaced the sensor and the oil pump
Tested oil pressure with a mechanical gauge and it seems to have below 4 psi at idle & would bump up if given a little bit of throttle. Anyone has similar issue that found a solution? Thank you.
 

Gopz

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Quicksilver 10w-30 and had it below the full mark. I will try to run it today and try it with half mark. Could it be possible that some debris blocking the oil passage to the sender?
 
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Gopz

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Update: I have tried running it with the oil on the halfway mark. No luck. The oil light would turn off if i give it high rev upon starting but as soon as i lower rpm to idle the light would turn on again
 

pvanv

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You could have a clogged oil pickup, or a clog in the sender port.
 

Gopz

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I have dug further. And found the main crank bearings are out of spec. Its probably why its not holding pressure at low rpms. Cyl and piston looks healthy.
 

MattFL

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If you want to run it longer before a rebuild, you can try thicker oil to see if it will hold pressure better. Maybe 10-50 or 10-60.
 

pvanv

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If your bearings are that loose and the oil strainer/pump/sender are good, it's time for new main bearings... Since the conn rods don't use bearing inserts, check those clearances. Might be time for new rods as well.
 

Gopz

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I have succesfully rebuilt the motor new rings new main bearings new oil pump and sender clearance on conn rods are still within spec. I dont understand i still have don’t have pressure on idle. What are other components related to oil pressure? What about the plunger
 

MattFL

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Does that motor have an oil pressure relief valve, to be sure oil pressure doesn't get too high? If yes, maybe that has gone bad and is leaking a little oil when it shouldn't?
 

Gopz

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Does that motor have an oil pressure relief valve, to be sure oil pressure doesn't get too high? If yes, maybe that has gone bad and is leaking a little oil when it shouldn't?
I don’t think there is one other than the oil pressure switch.
 

Gopz

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If your bearings are that loose and the oil strainer/pump/sender are good, it's time for new main bearings... Since the conn rods don't use bearing inserts, check those clearances. Might be time for new rods as well.
Sir what does the plunger do in relation to the oil pressure?
 

pvanv

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The "plunger" is the pressure relief. Should hold about 40 or so PSI. It could be stuck partially open. I have seen that.

3V2076200M​
PLUNGER​
$26.35​
 

Gopz

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What about the oil pickup tube/hose i noticed that it became hard
 

pvanv

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Maybe due to an overheat. In that case, maybe new is a good idea. BUT still check to see if the plunger is stuck.
 

Gopz

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Maybe due to an overheat. In that case, maybe new is a good idea. BUT still check to see if the plunger is stuck.
It was indeed the Plunger that was stuck open! Thanks. After a lot of parts replaced finally got it fixed
 

MattFL

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Thanks for posting the resolution, maybe that will help someone else in the future.
 
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