2005 f115 oil pressure issue

[Hourstonglassic]

My new to me f115 oil alarm goes off after the iac comes off and the rpms drop on initial startup, I've put a manual gauge on and when it's first started its 70psi and then drops to around 50 then it's somehwat sparratic it never drops to 0, but it seems like once it's soemwhat warmed up oil pressure stabalizes and at idle it's 50psi and at higher rpms it's 70psi and the alarm doesn't go off again, went for a good long run wot of 5700 no knocks, ticks and oil pressure stay steady, but when I go to fire it up the next day It happens all over again. Compression is even on all cylinder at 180 , the motor has 2015hrs on it

Could this be my oil pump pressure switch? I have also replaced the oil pressure switch on the top of power head and same result, before I tear into it and spend some money I figured some input from this site will help me along in the right direction

[Bluefish]

You have verified the oil pressure with a mechanical gauge, and the readings look good. This may sound a little crazy these motors are very voltage sensitive you should check your batteries, stator and rectifier. I had similar issues and my stator was going bad.

[almetelo]

at idle it's 50psi

In fact service manual for you motor say oil pressure must be 49.8psi or higher at idle so if you have +/- 50psi at idle so you have a oil pressure issue.

Maybe a new oil pressure pump fix the issue.
Hope Mr. Bolt (or any other) can give his opinion/experience about this.

So far haven´t tested the oil pressure on my F100 but can say that for my F40 SM says 21psi or higher at idle and I have +/-50psi

[fairdeal]

In fact service manual for you motor say oil pressure must be 49.8psi or higher at idle so if you have +/- 50psi at idle so you have a oil pressure issue.

? 49.8 .... +/-50 ...isn't that pretty much the same?

So far haven´t tested the oil pressure on my F100 but can say that for my F40 SM says 21psi or higher at idle and I have +/-50psi

ahh - so if the SM gives a "minimum" number - one should actually expect 2X that?

A strange way to write a manual!

[Hourstonglassic]

I'll double check the voltage in the batteries and stator output, but everything was ok when I checked the other day, batteries are brand new 2x 1000 cranking amps, new battery cables to motor.

The oil pressure stabilizes after it's warmed up a bit 50psi@idle and 70@higher rpm but before it warms up the pressure bounces around and it does drop below 21psi which sets the alarm but it never goes as low as zero, and if I bring up the revs the pressure will jump to 70, looking at other posts on here I'm leaning towards the oil pump but I want to be sure before I tear it apart

[almetelo]

before it warms up the pressure bounces around and it does drop below 21psi which sets the alarm but it never goes as low as zero,

If oil pressure drops to 21psi no douth that you have a oil pressure issue.
If my motor I wouldn´t even start it again untill changed the oil pump because you can seize the motor than you have a huge fixing costs or have to sell the motor in parts.

When oil and filter was changed last time?

[Hourstonglassic]

The motor is new to me and I changed it as soon as I got it it was a bit dark but I like my oil clean, I've been tinkering with it now for a couple hrs taken it for a couple runs with no issues other than when first started for the day

[Hourstonglassic]

My motor does not have and oil pressure sender just and on off sensor which will set the alarm if pressure drops below 21psi, the yds will only tell you on my model if the switch is on or off, I have put a mechanical gauge and I know there is something going on with oil pressure not a sensor

[boscoe99]

An F115 does not output oil pressure. It uses a pressure switch that is either open or closed. Completely different from an F225. Only thing those models have in common is the colour.

Do you have a Yamaha tachometer that is indicating low oil pressure? If so it is either the switch or the oil system that is the problem.

[Hourstonglassic]

I know the switch is find its brand new, and yes I have the yamaha digital tach and it is indicating the oil alarm, and I have out a mechanical
Gauge on the motor to confirm oil pressure on start up does drop below 21psi

Is there anyway I can put a diff oil in the motor, thinner or thicker to bring up the oil pressure to confirm a weak oil pump or the pressure valve in the pump is sticking ? I would like to figure that out before I pull the power head

[boscoe99]

I know the switch is find its brand new, and yes I have the yamaha digital tach and it is indicating the oil alarm, and I have out a mechanical
Gauge on the motor to confirm oil pressure on start up does drop below 21psi

Is there anyway I can put a diff oil in the motor, thinner or thicker to bring up the oil pressure to confirm a weak oil pump or the pressure valve in the pump is sticking ? I would like to figure that out before I pull the power head

I would certainly try a different grade of oil before I would perform surgery on the motor. Maybe something thicker, maybe something thinner.

While I am not a fan of oil and gasoline additivities I might try some brand of engine oil cleaner, that more than likely won't work. When you are down to nothing you got little to lose.

[99yam40]

I do not really know much about the Yamaha oil pumps, but would think they would be close to automotive pumps that have a pressure relief valve that regulates the oil pressure.

oil pumps should be positive displacement, so not much should reduce pressure except a relief valve,pick up screen plugging up(restricting), or sucking air.
I could be way off base on this though


Maybe someone with the knowledge on them could enlighten us on the subject.


Best thing to do would be hook your gauge to a different Motor to see what it does at start up and warm up to compare.

[fairdeal]

...Seriously, I don't think changing the viscosity of the oil will solve your oil pressure alarm issues. My guess is you can probably run that engine with the oil pressures you have in there now...

This reminded me of the thread from a year or so back - also F115 - also mysterious low oil pressure:

http://www.yamahaoutboardparts.com/f...e-th23414.html

[Hourstonglassic]

Tried a 15-40 oil didn't help was worse on start up until it warmed up abit then totally fine, power head is coming off tomorrow

And putting a mechanical gauge on also tells you oil pressure

[Hourstonglassic]

Pulled it apart today, into the shop Monday for a good cleaning and inspection, what should I be looking for inside that oil pump?