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Old 07-04-2022, 06:58 AM   #1
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Fuel economy twin 240hp Yanmar 4LHA-STP diesels

My two recents attempted purchases of Mainship 390s fell thru and am now looking at a 2002 Mainship 390 with twin 240hp Yanmar 4LHA-STP diesels. Does anyone have this setup? And can you advise either your actual fuel economy at cruise (and how many rpmís and speed in average conditions) or what speed you get at 2400 and 2600 rpmís (I found a chart that shows fuel burn at those rpmís but not sure how fast the boat goes at those turns). Also, any tips on maintenance or anything else I should know?
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Old 07-04-2022, 10:46 AM   #2
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I have the 2006MS 34. Not sure when MS started this line, may have been after 2002. With my twin yanmar 4 cylinder diesels ,running at 2200rpms and 10mph I get 1.5 mpg. I am going from a sight gage/tube on the single 250 gal tank. People are going to say that mpg is low but I just made a 12 hr round trip and ran 2200 rpms 95% of the time. People talk about my boat being a planing hull . Dont believe it unles s you want to run near 3300 rpms !
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Old 07-04-2022, 11:22 AM   #3
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Fuel economy

Thanks. Iíll be very happy if I can get that mpg on the 390 with the bigger engines. Appreciate your response
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Old 07-04-2022, 12:21 PM   #4
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The MS34 referenced above is the newer trawler usually called the 34T. It is roughly the same dimensions as older MS390 and should get roughly the same fuel economy.

When the MS34 owner says he has 4 cylinder Yanmars, he means the 4LH 240s, the same as on the 390.

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Old 07-04-2022, 01:37 PM   #5
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Fuel economy 390 twin Yanmars

Ok, wasnít sure. Iíd be happy with 1.5 mpg How about maintenance, anything to be aware of? And have you done 1000 hour service? Any idea as to cost per engine?
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Old 07-04-2022, 01:54 PM   #6
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Originally Posted by Lshulan View Post
Ok, wasnít sure. Iíd be happy with 1.5 mpg How about maintenance, anything to be aware of? And have you done 1000 hour service? Any idea as to cost per engine?
Cost will be just short of staggeringÖ
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Old 07-06-2022, 03:16 PM   #7
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Originally Posted by Lshulan View Post
My two recents attempted purchases of Mainship 390s fell thru and am now looking at a 2002 Mainship 390 with twin 240hp Yanmar 4LHA-STP diesels. Does anyone have this setup? And can you advise either your actual fuel economy at cruise (and how many rpmís and speed in average conditions) or what speed you get at 2400 and 2600 rpmís (I found a chart that shows fuel burn at those rpmís but not sure how fast the boat goes at those turns). Also, any tips on maintenance or anything else I should know?
Check the Library under Miscellaneous. There is a MS400 fuel burn table for these engines. You should see similar results for the 390.
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Old 07-07-2022, 11:08 AM   #8
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We have twin 4lha-stp in our 400. At 1850 rpm, which is around 8 knots, we burn right at 4 gallons an hour, combined. At 2900 rpm, about 15 knots, we burn about 13 gallons an hour. Both 2,400 and 2,600 rpm would be an awkward speed for these motors, unless the 34T is different than my 400. You max out hull speed around 1900 RPM and don't start to "plane" until about 2800.



Just had the 1,000 service done to both of my motors, it ran right at $5,000, including replacing both raw water pumps.


The 4LHA is one of the best motors Yanmar has ever built. Take care of them and you will have very few issues. They do chew through belts though. I just replaced mine with serpentine belts.


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Old 07-07-2022, 11:47 AM   #9
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Fuel economy

2 mpg at 8 knots is great, Iíll be very happy with that and at the higher speed getting at or above 1 mpg is also good news. Thanks so much for the info Also the cost for the maintenance is also good news I had read that these engines need to be run for some portion at 2400 to 2800 which is why I asked.

Where are you located?
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Old 07-07-2022, 11:51 AM   #10
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From my experience owning a 34T for five years, you are exactly right about getting over hump onto plane. It takes about 2,800 rpm for the wake to smooth out, indicating it is planing, well sort of.

I too like the 4LH, one of Yanmar's best.

David

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