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Old 19-12-2005, 07:13   #1
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Full Power Trials - Yes or No?

I spent many years in the ship repair world while in the US Navy, and it was always standard practice to conduct full power trials during service life evaluations and post-overhaul trials.

So now I'm doing a survey/sea trial on an Endeavour 52 powered by a 4TH2 turbo Yanmar. I asked for a full-power trial of 30 minutes duration, and the broker went ballistic. Said "no boat owner would allow that" and he wouldn't on his personal boat either.

OK - so what am I missing here? Is this another of the great myths of the sea that says 'thou shalt not run your diesel at full power?' I suspect he is concealing an overheating problem.

So - how do the captains on this board feel about full power trials?
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Old 19-12-2005, 07:18   #2
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Don't know that I would mandate a 'full' power trial as most diesels are designed to run at 80% under load for extended periods not 100% as far as I know.

I would however run it at 80% for a while to make sure not overheating etc. If it's going to have an overheating problem bet is shows rather quickly than taking a 1/2 hour. IMHO
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Old 19-12-2005, 07:58   #3
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If you look in the Yanmar engine manual, (at least on the naturally aspired engines) it specifies a cruising speed RPM and a higher max operating RPM at which the engine can be run for specific limited lengths of time. If you have reasons to be suspicious about this engine I would suggest that you include a more normal contingency for a "motoring trial at the full range of RPM recommended by the engine maunfacturer". When you get on board I would suggest that you pull out the manual (or download a manual in advance and bring it with you to show the broker or owner if they have questions) and then run the engine at the recommended cruising speeds and max operating speed. That should permit you to see if you have any problems.

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Old 19-12-2005, 08:22   #4
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Yanmar normally* specifies both “Continuous” (often @ 3400 - 3600 RPM), and “1 Hour, or Maximum” (often @ 3600 - 3800 RPM) rated horsepower output for their diesel engines.
I’m not certain what you mean by a “Full Power” test, but can’t see any legitimate reason to prohibit a one-half hour test at maximum RPM. Any test at less than “Continuous” output is worthless.

* I don’t have any specific information on the 4TH2 Turbo.
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Old 19-12-2005, 09:43   #5
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I believe you are talking about the 4JH2-TE 75hp engine.
If he won't let you do a seatrial at max continous rpm, accept that. Base your offer on needing a new engine because of the broker, or walk away.
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Old 19-12-2005, 10:39   #6
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THE OFFICIAL

The official specs for power output on your, yes, 4JH2-TE are as follows.

Full load speed 3600rpm

No load speed 4000rpm

Idle speed 800rpm

Prop matching speed(prop for) 3300-3700 rpm

Approx. hull/cruising speed 2500-3100 rpm

This info is from my Yanmar Tech Training Manual. The course I was sent to last spring.

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Old 19-12-2005, 11:21   #7
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Correct model info is 4JH2-DTE, 88hp version. Broker had the model # wrong....

Many thanks for the replies here - I am searching for a downloadable Owners manual since the original is no longer aboard. Already purchased the SELOC repair manual.

IMHO.. these forums are a great resource.. how did anyone ever sail before we had the Internet?
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Old 19-12-2005, 11:38   #8
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Mark, Pat above is an experianced Yanmar Mechanic. If he say's you can run it hard, you can. But do note that Pat has stated, "Max continuose RPM".
You will or should find two spec ratings. One will be continuose rated RPM and the other is Max short term duration. It maybe worded differently of course. The short term max RPM WILL cause engine overheating and probably smoking. So you could take it to those revs to check all is OK but, I personaly would not keep it there for more than a few minutes. The max continuose RPM should be the test point and you should not see black smoke nor engine overheating at this RPM.
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Old 19-12-2005, 12:44   #9
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My surveyor here in Florida requires a full throttle run for a few minutes.

It sure smoked out an overheating problem on my boat.

(Perkins 4-108, 7 years later I still have the same problem after having changed or overhauled every single piece of the cooling system...The only remaining cause must be a desgin flaw, not big enough raw water intake...)
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Old 19-12-2005, 16:03   #10
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No there is probably no problem at all. The Max rating on the perkins is for intermitent use only and should not be run there for more than a few minutes and then only rarely. The continuose RPM is significantly lower.
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Old 19-12-2005, 17:29   #11
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Yup the max rating is 4000 RPM, the max continueous RPM is 3000.

The engine will slowly but surely overheat if I run it over 2600 RPM for more than 5 minuttes, so yes, there is a problem, I have just not found it.

(Have tried different props)
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Old 19-12-2005, 17:53   #12
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There is no reason

to not run the engine at full throttle for an extended period of time. No good engine is going to desintigrate because it does what is is intended to be able to do. When the fuel system manufacturer designed the governing system, they allowed for the posibility that some owners would run the engine at full throttle for extended periods of time.
If the broker won't allow this, either he is hiding something of he is just stupid. In either case, you have been handed a significant bargaining chip.
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Old 19-12-2005, 18:37   #13
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Hmmm, CSY, that is significantly down. I know you know all the following, but I'll just throw thoughts out there, just incase yuou have over looked something.
I presume the engine will pull close to 4000. If yes, then over proping isn't the cause.
Too small an exhaust dia. for it's run length, to much restriction via either bends, water traps or outlets can also cause heat to build up. Plus too much exhaust pressure can cause a higher head of water pressure for the cold water pump, thus it doesn't move as much water. Faulty thermostat or wrong temp thermostat. Wrong size water pump pulley on either cold water and/or internal circulation pump or main engine drive pulley and thus either/or pumps are not spinning at correct speed and the water isn't circulating effectively. Too small an outlet or inlet for the cold water pump and it's not pumping to capacity. This can easily happen if the hose runs are some distance and one that is easy overlooked is the skin fitting diameter. The other end is the exit into the exhaust can be too small and restrict flow.
Scale in engine cooling jackets.
If you have an external cooling device such as a keel cooler, make sure they are NEVER painted. Even one coat of paint will stop it from cooling effectively and engines overheat real fast.
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Old 19-12-2005, 20:36   #14
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Okay Mr. Wheeler, thanks for the input.

No keel cooler, just a very conventional setup from the factory, and no modifications.

Tried different thermostats, no change.

Yes, the engine will pull about 4000 RPM at full power while underway, and 3800 RPM tied to the dock so over-propping is not an issue.

The engine sits failry deep in the boat with a long run under the cockpit to the outlet in the stern, so there is some distance and vertical climb for the water and exhaust to exit.

The over-heating problem is not really a big problem as I run the engine @ 70% of max continueous as a general rule, that is 2100 RPM., or if I am in a hurry, 2400 RPM.

The few times I go full power is in emergency situations such as when a bridge is trying to close on top of me, or to avoid collisions, but only for a few seconds.

Still irritating to have a "bug" in the boat, and if I could pinpoint the problem, and fix it without breaking the bank, I would.
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Old 20-12-2005, 08:43   #15
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Gregb from this board is having the same problem with one of his Perkins engines. Like CSYman he just cannot figure it out. Is it a Perkins problem? The guy that I bought my boat from had the same problem with the Perkins 4-236 that it had at the time.
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