I have by now put almost 800 hours on my Yanmar
4JH3HTE, for a total of 1600.
When I bought the boat, the engine
had 830 hours and it smoked like hell. I almost refused to close the deal, and the seller spent tons of money
trying to rectify it, overhauling the injection pump and turbo and paying for tons of mechanics' time trying to figure it out. No one ever did. Finally my really tough surveyor
who is a specialist in diesel
engines said "well, it's just a smoky Yanmar
; I wouldn't worry about it." And so I gave up and closed the deal. That was 5 years ago.
The smoke is gray-bluish, and comes out in billows on startup. The smoke just about disappears at normal operating temperature and speed. Since the engine
doesn't consume any oil
(maybe half a liter between 100 hour changes), I presume that this is not oil
smoke, but fuel
But I had the injection pump out two years ago, and had it on a test stand with the full battery
of tests, and it checks out perfectly. I have replaced all the injectors with new. Nothing makes any difference.
The other problem I have had intermittently is that the engine will not develop full revs. Sometimes just under load; sometimes even in neutral. It will cut out and sometimes behaves like a gasoline (petrol) engine which has a miss. Usually this happens at 3200 to 3500 RPM
, so I don't really care, as I don't normally operate the engine at that speed. But once two years ago it happened even at 2500 and below, which was really alarming. I had the engine checked in Jersey by a really good mechanic
. He washed the turbo with the special Yanmar expensive turbo wash, and checked everything he could, and couldn't find any problem. It was after that that I had the injection pump off and put on the test stand, and nothing wrong was found with it. Interestingly, after I put the pump back on, the problem disappeared for a while.
I have checked and rechecked everything I can think of. The fuel
system seems fine; I have the tank cleaned out regularly and have never found a speck of crud or drop of water
in it (we get really good fuel over here). I have dual Racors but the filter elements never get dirty, even when I use the two micron ones. I change them regularly nevertheless.
The fuel lift
pump is a roller cell job which is integral with the injection pump and has checked out on the test bench.
The exhaust elbow
is clean with no carbon build up, indicating, I think, good combustion. I check it regularly but have never needed to even clean it.
The engine starts extremely well (which I take to be a sign that compression
is good), so well that I have never used the air preheater even in sub-freezing weather
. The engine has always run smoothly and well at normal operating speeds. Oil pressure and coolant
temp always normal.
The Yanmar dealer who worked on the engine on behalf of the seller 5 years ago confessed that they had concluded that the bores were polished (nice of no one to tell me). But that can't be -- with neither any oil burning nor any starting problems.
I might suspect boocon or governor -- but these were checked out on the bench as part of the injection pump. It seems like overfueling at startup/idle, and perhaps underfueling at high RPM
, but no one has been able to determine any concrete problem.
I've lived with these problems for 800 hours and I guess I could live with them for another 800, but it bugs me that such a simple, non-electronic engine could have such an elusive problem.
I've asked all these questions on here before, but in the mean time we have a lot of new people and even the old timers may have accumulated new experience, so I'm asking it again. Anyone have a clue?