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I have a Yanmar 2 QM15 with about 500Hr since it was rebuilt. The oil pressure
is fine when I first start up 40 psi and its ok for about 2 hours running at
3000 rpm. The oil pressure starts to drop below 20 psi. The alarm goes off and I
reduce the rpm to 2200 or less and the alarm stops and the pressure is low but
it seems ok. Its around 18 psi. If I run the rpm back up the pressure goes up a bit but not enough. This problem just started up, and I at a loss
about to do about it. I don't think its the sensor because it works fine when I
first start up.
I've changed the oil and filter and it still happens. I'm not using a Yanmar
filter but that should not matter, I use shell oil rotella t 15w 40 and have
been using the same for years. I know the original owner of my boat had the
same type of problem and thats why he rebuilt the engine. I can't get in touch
with him. I' looked on the web and have found no answers. I have put the 500hr
on and have been good about all maintains, Ive had no other problems with it
other then its very hard to start when its cold out, below 50F but thats not a
problem now.
Any ideas would be helpful, I'll be in a place where I can get parts this week.

Thanks Stephen
 

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I have a Yanmar 2 QM15 with about 500Hr since it was rebuilt. The oil pressure
is fine when I first start up 40 psi and its ok for about 2 hours running at
3000 rpm. The oil pressure starts to drop below 20 psi. The alarm goes off and I
reduce the rpm to 2200 or less and the alarm stops and the pressure is low but
it seems ok. Its around 18 psi. If I run the rpm back up the pressure goes up a bit but not enough. This problem just started up, and I at a loss
about to do about it. I don't think its the sensor because it works fine when I
first start up.
I've changed the oil and filter and it still happens. I'm not using a Yanmar
filter but that should not matter, I use shell oil rotella t 15w 40 and have
been using the same for years. I know the original owner of my boat had the
same type of problem and thats why he rebuilt the engine. I can't get in touch
with him. I' looked on the web and have found no answers. I have put the 500hr
on and have been good about all maintains, Ive had no other problems with it
other then its very hard to start when its cold out, below 50F but thats not a
problem now.
Any ideas would be helpful, I'll be in a place where I can get parts this week.

Thanks Stephen
I have read about some filters causing that problem, maybe try a Yanmar filter?

Possibly, the electric sensor is heat sensitive, Maybe try a new sensor, or temporarily hook up a mechanical gauge.

Or perhaps the pressure relief valve is failing, maybe effected by heat?

Or maybe the oil pump is getting tired?

If none of the above, maybe the engine bearings are somewhat "loose" after heating.

"Rebuilt" ? whole lot of variables there. Rebuilt by whom & what parts were replaced?
Paul T
 

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I had a similar problem with my Universal diesel. My engine has a separate oil pressure switch (for the beeper) and oil pressure sender (for the gauge). The switch and beeper were never activated, but the gauge would read 50 PSI at start, then slowly drop to < 10 PSI. The problem was that heat from the engine would warm the sender, and increase the electrical resistance, and give me a (false) low reading. I put a new sender in, and moved the sender away from the exhaust riser. Problem solved.

If you have discrete sender and switch, yet are seeing low oil pressure, and triggering the alarm, then I would look carefully to see if you have adequate pressure (test with a mechanical gauge) before swapping anything. However, if you have a combined sender and switch, then I would order a new one and replace as the first step.
 

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What weight oil are you using?

The oil weight will loose viscosity as it heats up. If you are using 30 Wt. you might try going to 40, AFTER you check with a real gauge.

Just a thought......
Greg
 

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Discussion Starter #6
I'll be in the USVI by the end of the week and I'll pick up a new sender switch.

Thanks
 

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The oil also gets a bit tired toward the end of the season. I have noticed that end-of season oil (hot) reads about 28 psi at 1700 rpm and new oil (hot) reads about 35 psi. I use my old favourite oil 15/W40 mineral.
 

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I know this post is a little stale , but it interests me because we have a 2QM15 with the same problem . I first put on a mechanical pressure gauge, it confirmed the electric gauge , then a new electric gauge and sending unit , bought a new oil pressure regulator and shimmed it . Used a Yanmar oil filter . All to no avail . The manual says 4psi at idle is normal but my warning light and buzzer were coming on at idle . Manual also says the things that cause low oil pressure are loose crank bearings , cam bearings, loose rocker shaft . No mention of loose oil pump , a omission for sure . I'm starting to get bummed out , I talk to mechanics I talk to the Yanmar dealer then I was talking to my homeless buddy that actually is not homeless because he lives on his bicycle , he says "have you tried Lucas oil treatment ? " I said no but I will , and I did . Problem solved .
 

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I hope that you bought your "homeless buddy" a meal to compensate him for his consultation. :)
 
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