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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 05-27-2014
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Yanmar 40 HP 3JH3E engine problems

Hi Everyone

The Yanmar 3JH3E 40hp in my boat has been a great work horse. Last season I replaced the primary and secondary filters and I have bled the system.

What I am finding now is that after running the engine in gear for 30 minutes or so, it tends to just drop power and then rev up again. Occasionally it does drop power and cut out completely, but most time it just looses revs then up again. I normally run the engine at 2500 revs, but this also happens when running at high revs of around 3500. This weekend the engine ran smoothly for 3 hours (no wind on the east coast of England) and then stopped... but each time it happens it starts quickly and off we go again.

The engine sounds great, no overheating, no smoke of any colour and has plenty of power

Just wondered whether you had any idea, before I get the professionals in the look at it?

Last edited by johnlbailey; 05-27-2014 at 08:06 AM. Reason: more information
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Re: Yanmar 40 HP 3JH3E engine problems

Sounds like a suction side air leak... filter seals/gaskets? suction side bleed screw?
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Old 05-27-2014
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Re: Yanmar 40 HP 3JH3E engine problems

bad filter? or filter gasket/seals would be the first thing to check/replace
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Old 05-27-2014
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Re: Yanmar 40 HP 3JH3E engine problems

Possibly an air leak in the downstream side of the fuel delivery system, bad seal in the filters or connections. Maybe the tank is not venting properly, try running with the filler cap off or loose. Maybe debris being sucked up against the feed pipe screen, if there is one.

If you pressurize the system from the tank outlet downstream by using a squeeze bulb from an outboard or an electric pump, fuel may leak out at any bad connection of filter mating surface.

You could also try a separate gravity fed tank, bypassing the permanent tank.

Paul T
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Re: Yanmar 40 HP 3JH3E engine problems

Quote:
Originally Posted by dabnis View Post
Possibly an air leak in the downstream side of the fuel delivery system, bad seal in the filters or connections. Maybe the tank is not venting properly, try running with the filler cap off or loose. Maybe debris being sucked up against the feed pipe screen, if there is one.

If you pressurize the system from the tank outlet downstream by using a squeeze bulb from an outboard or an electric pump, fuel may leak out at any bad connection of filter mating surface.

You could also try a separate gravity fed tank, bypassing the permanent tank.

Paul T
Like that bolded bit......
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Re: Yanmar 40 HP 3JH3E engine problems

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Originally Posted by Faster View Post
Like that bolded bit......
Never had it happen to me, but there are not too many wasps or hornets on San Francisco Bay, only know what I have read. John doesn't say where he is from? I think there are a lot of bugs "back east"?

If any part of the vent system is rubber hose a crimp may develop over time?
Kind of sounds like "slow starvation" I think a bad filter, either plugged or air leaky, would be more constant?

Paul T
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Re: Yanmar 40 HP 3JH3E engine problems

Yeah.. slow vent starves feed... stoppage allows tank to equalize, OK for a while and starts over again...
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