 | TMS Poloshirt winner |
06/05/08 13:29
My problem is this. I have a Yanmar 2GM20 of indeterminate age (possibly 1990). The engine is raw water cooled and the exhaust system has a Vectus exhaust box. It starts perfectly every time. It blows some smoke on starting and generally clears from a dark cloud to a small amount of what i would consider slightly smokey exhaust providing I dont push it too hard.
I had occasion recently to use the engine flat out trying to buck a spring tide, The engine was smoking quite heavily. I decided to run the engine on the pontoon to see if I could detect the smoke type and quantity more accurately. To my alarm as I watched (I was running the engine as somewhere approaching 4000 revs in gear while tied to the pontoon) The exhaust water turned from clear to black. There was no sign of any oil on the surface of the water after it had been ejected from the boat but it had the appearance of black dust dispersing in the water. When the revs were reduced the water returned to its clear state.
I would be grateful if anyone could help me with diagnosis of this situation.
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| TMS Poloshirt winner |
06/05/08 14:56
 Sounds like the good runs have loosened all the built up carbon from low rpm running and then blown it all out. w.
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| TMS Poloshirt winner |
07/05/08 19:06
Hi Richard, this sounds to me like the injectors need a birthday, but i will report back after discussing with a couple of 'experts', Scotty
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| TMS Poloshirt winner |
08/05/08 09:31
Black smoke would certainly point to injectors over fuelling but the black dust on the water and the unusual engine load suggests the engine isn't used at high rpm much is why I think it sounds like built up carbon. .. as no oily film reported on water. Black smoke could also be injector pump problems, dirty or blocked air filter or things like choked valves from the carbon build up... Did the black smoke stop when you reduced the rpm too? Did you try increasing them again? Check the simple things first thou! W.
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| TMS Poloshirt winner |
08/05/08 10:17
Dear all Thanks very much for the replies so far. After posting here I also consulted with Tony Brooks of tb-training who offers free advice. (Cathy I appreciate that your excellent website must be supported by advertising and I have no wish to undermine this, however I hope you dont mind me putting up this reply which includes a link to his website link as it appears to to be very useful even for us non canal boaters) Dear Richard This is classic overloading of a diesel engine and assuming the prop is not fouled it is caused by propping the boat for maximum economy and not maximum engine speed. It probably does the same if you snap then throttle open as the engine accelerates. The injector pump on most diesels is capable of delivering far more fuel than the engine can burn. This aids cold starting but when the engine is running the governor in the pump ensures only the correct fuel for the speed you set is delivered, so all the fuel burns to water vapour and carbon dioxide. If anything artificially holds the engine revs down the governor keeps increasing the fuel supply to try to accelerate the engine, but because the engine will not accelerate there is too much fuel and that produces H2O CO2 CO and carbon. You have been seeing the carbon particles. Your engine will almost certainly be propped to absorb maximum torque and that point is somewhat slower than maximum speed. This is fairly normal on all but go-faster boats. I would suggest that if you slightly eased the throttle you would maintain the speed but reduce the carbon as the governor reduces the fuel delivery. I think all is normal, but check any air cleaner is free of obstruction, that the engine case is not obstructing the air supply and that no one has blocked any engine breather vents. I can not totally rule out a partially blocked exhaust but I would expect that to cause overheating as well and you do not mention that. If the engine has a lot of hours on it you may find the injectors need a service, but if its cold starting well and the smoke is not embarrassing I think I would leave it. Tony Brooks www.TB-Training.co.uk
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| TMS Poloshirt winner |
08/05/08 10:32
 Hi Richard, seems you probably have the answers now. If the injectors are 'hosing' and not 'atomising' the fuel, due to the fuel tips on the injectors being in poor condition etc, then an injector service or exchange would possibly be the next thing to consider. I too noticed similar things happening on one occassion last season when pushing into Portsmouth harbour on the spring ebb. I throttled back a little maintaining the same SOG and the black soot stopped. Best of luck, Scotty
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| TMS Poloshirt winner |
15/05/08 09:54
Hi Scotty Guess where I was at the time ..... you guessed it .. The small boat channel entering Portsmouth Harbour on a spring ebb. Regards Richatd
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| TMS Poloshirt winner |
15/05/08 18:31
Hi Richard , where are you moored? I'm up channel, Fareham lake, on a swinging mooring at Wicormarine , near West end of Portchester. The photos you have in 'Gallery' of boats on a pontoon at sunset look familiar....Scotty
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| Edited: 15/05/08 18:36 |
| TMS Poloshirt winner |
15/05/08 21:28
Did you get a definative diagnosis from a mechanic Richard? W.
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| TMS Poloshirt winner |
15/05/08 22:30
Scotty ... yes Wicormarine ... Pontoon berth E11 Well spotted, Southernmost Pontoon shoreward side, look out for me and well have a chat. Wolfie ... no not yet, however I have an old mate of mine who is pretty good with those smokey things coming up for a visit in the next couple of weeks, for a look at the engine and of course for a sail. Richard
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| TMS Poloshirt winner |
15/05/08 22:45
It's a small world Richard. The 'expert' advisor I have on mechanical things whose name is Vic, a marine engineer, is living on his boat, a white Elizabethan 31, in the seaward side of the yard until next week. Give him a visit and discuss, and say hi from me if your down this w/e. I'm on swinging mooring 24. The white hulled Twister with the windmill and Monitor on the back, just off to the right from the end of the jetty. cheers, Scotty.
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| Edited: 15/05/08 22:51 |
