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Old 09-08-2016, 13:39   #1
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Yanmar 3jh4e high fuel consumption

I have two Yanmar's and run them at the same rpm around 2k. One of the engines uses a lot more fuel then the other between fill up's. Any ideas.
No smoke or leaks.
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Old 09-08-2016, 17:09   #2
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Re: Yanmar 3jh4e high fuel consumption

What's "a lot more" in percentage terms?

Are both engine hours going up by the same amount between fill ups?

Are you running them one at a time or both together?
If both together, are you sure they are both running at the same RPM? Are you judging by a rev counter or by tuning to "beat frequency".
Rev counters can easily be 1-200 rpm out.

Do you have an extra drain on one engine such as a large alternator, eutectic freezer compressor etc?
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Old 09-08-2016, 17:20   #3
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Re: Yanmar 3jh4e high fuel consumption

I think the one engine is using 20% more. I usually run both together, but motor sail too with one. I keep the hours close though.
I thought that both alternators charge the battery bank together?
The ignition switches are new. I didn't know they could be that far off. Maybe that is the ticket.
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Old 09-08-2016, 18:47   #4
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Re: Yanmar 3jh4e high fuel consumption

How do you know that the engines are consuming different amounts of fuel?


Couple of thoughts:
- Two separate tanks, and both fuel return lines are going to the same tank...
- Two different size propellers, and running at the same RPM causes more load, hence more fuel consumption on one engine than on the other....

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Old 09-08-2016, 19:17   #5
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Re: Yanmar 3jh4e high fuel consumption

Quote:
Originally Posted by DougR View Post
How do you know that the engines are consuming different amounts of fuel?


Couple of thoughts:
- Two separate tanks, and both fuel return lines are going to the same tank...
- Two different size propellers, and running at the same RPM causes more load, hence more fuel consumption on one engine than on the other....

DougR
I delivered a twin engine trawler once that was rigged like that - fuel return all went back to the port tank - a bit of a problem when we started out with full tanks running off the starboard tank.

But I doubt that a Lagoon with engines in the hulls runs the fuel return like that.
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Old 10-08-2016, 04:00   #6
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Re: Yanmar 3jh4e high fuel consumption

Same props installed last year. Returns go to same tank. Going to break down and call Yanmar.
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Old 10-08-2016, 04:14   #7
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Re: Yanmar 3jh4e high fuel consumption

Quote:
Originally Posted by Fearnow View Post
Same props installed last year. Returns go to same tank. Going to break down and call Yanmar.

Does that mean the returns go back to the tank that the respective engine is drawing fuel from? Completely isolated from the other engines' fuel supply?


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Old 10-08-2016, 04:33   #8
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Re: Yanmar 3jh4e high fuel consumption

Each ending has it's own fuel tank, with feed and return lines.
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Old 10-08-2016, 11:03   #9
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Re: Yanmar 3jh4e high fuel consumption

Quote:
Originally Posted by Fearnow View Post
I have two Yanmar's and run them at the same rpm around 2k. One of the engines uses a lot more fuel then the other between fill up's. Any ideas.
No smoke or leaks.
Just resolved a similar problem. Tachos are run from the alternators. One alternator had a different width pulley whhich meant the belt rode higher. When i measued the rpm of the engines with a hand tacho found that one engine was runnung 200rpm faster than the other. Still proving the thory but am confident I've found reason for higher fuel consumption.
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Old 10-08-2016, 16:42   #10
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Re: Yanmar 3jh4e high fuel consumption

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Originally Posted by Fearnow View Post
I have two Yanmar's and run them at the same rpm around 2k. One of the engines uses a lot more fuel then the other between fill up's. Any ideas.
No smoke or leaks.
Could I ask how many litres per hour are you using at 2000 rev's per engine.
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Old 11-08-2016, 15:40   #11
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Re: Yanmar 3jh4e high fuel consumption

One engine has a partially obstructed exhaust?
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