Advice from engine gurus please!

Robin

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Looking at some potential 47 foot motor yachts to buy in the USA and one has Cummins 6BTA5.9M2 300hp engines, another has the same basic engine but 6BT.5.9 at 210hp (turbo but no aftercooler). Are these good engines? I have heard the ones at over 300hp have raw water cooled aftercoolers that can be troublesome, but up to 300 have freshwater engine water cooled ones and are still fairly long lasting. Any comments? Engine hours on the 300hp ones are 1,950 and 2432 on the 210hp ones. The 210hp one is cruised at 8-9kts @ 3.5gph (US) max 15kts, 300hp one can apparently reach 18kts, slower speed is fine by me however.

Also looking at two others with Cat 3208TA 375hp engines which seem a popular USA choice, good or bad comments?

This is outside my comfort zone after 40 some years of rag and stik and max hp of 50!
 

ccscott49

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Both of the engine types are fine. IMHO, Good reputation for both, but I'm sure there are lots of more engine types than me here who will give you the full story.
The hours are nothing for engines of this type.
 

Latestarter1

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Looking at some potential 47 foot motor yachts to buy in the USA and one has Cummins 6BTA5.9M2 300hp engines, another has the same basic engine but 6BT.5.9 at 210hp (turbo but no aftercooler). Are these good engines? I have heard the ones at over 300hp have raw water cooled aftercoolers that can be troublesome, but up to 300 have freshwater engine water cooled ones and are still fairly long lasting. Any comments? Engine hours on the 300hp ones are 1,950 and 2432 on the 210hp ones. The 210hp one is cruised at 8-9kts @ 3.5gph (US) max 15kts, 300hp one can apparently reach 18kts, slower speed is fine by me however.

Also looking at two others with Cat 3208TA 375hp engines which seem a popular USA choice, good or bad comments?

This is outside my comfort zone after 40 some years of rag and stik and max hp of 50!

6BT 210 is as simple as a wheelbarrow, entered production in 1987 and STILL in production today. Small change was made to timing in 1999 to make engine IMO emissions compliant, other than that nothing. 210 proper i.e SAE 40 degree fuel horsepower at 2,600 rpm, straight turbo engine. 10,000 hour plus motor without catching a breath. Low smoke low fuel consumption with minimal maintainence costs, super engine.

Early 6BTA 300 is different beast, later 330 and 370 were good motors the early 300 was not. If engines have US made welded SWAC Salt Water Aftercoolers avoid like the plague! Welded design prevented cooler maintainence, plus the fact that heat exchanger tubes were rectangular in section not round (How did Americans ever send a man to the Moon!). Tubes panted due to pressure waves created by turbo, tube would fail, letting sea water go straight into the engine, resulting in tears before bedtime.

Motor was completely redesigned, key element was fitting decent British Serck aftercooler, marine grade alloy, bolted constuction with cupro nickel heat exchanger with ROUND tubes. Until the 6 BTA 315 revamp Denso pump had no LDA, and engine an over generous turbo compressor housing, nail motor and it will black smoke like hell until turbo catches up with the propeller. Cummins paid for many engines to be modified under policy, but few escaped though the net.

If you want to post me some pictures and ESN #'s I can tell you straight away if 300 is worth serious consideration.

CAT 3208's 370 rating was very reliable, tad jucy as well as being a little smoky.

Good hunting
 

Robin

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Many thanks. That explains perhaps why so many used boats for sale with Cummins 300hps have comments like 'one engine replaced at... ' . I sort of smelled a little rat somewhere! One boat I saw listed with 300hps was re-engined after 5 years and then one of those replaced again 5 years later. Favourite at the moment is the 210hp version because the boat with that is itself about as close to what we want as we could hope for and nearly all the gear new.

Thanks again, much appreciated.
 
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