No Upper End RPMs

[kenvail]

I was on a two-week trip around Long Island recently and developed an engine problem with my Yanmar 3JH4E diesel engine. I was getting a lot of blue exhaust smoke, an oil sheen on the water and couldn't get the engine above about 2,000 rpms under load. I changed both fuel filters but it didn't change the symptoms. Any ideas?

Thanks.

 

[kappykaplan]

My experience with oil sheen on the water says mixing elbow. But I had black smoke, not blue.

 

[Steve Dion]

I would agree about the mixing elbow. Lots of info in the archives.

 

[NYSail]

Mixing elbow or fouled prop

 

[frankies56]

Mixing elbow or fouled prop

I agree sounds like you prop is fouled, or mixing elbow. but you are giving it more fuel and it not using it that is why you see the black smoke. take a dive and look at your prop. and see if you did not wrap up a crab pot line

 

[kenvail]

I wanted to let all of you know who offered your good advice, that I found the problem and have had it fixed. It turns out that I had a badly fouled injector. I replaced all three and it now runs like a top. Just in time for next season! At least it is fixed and next season has one less project. Thanks again and, for those of us in cold regions, have a safe winter.

 

[kenvail]

I recently went to the Atlantic City Boat Show and sat in on an "ask a diesel mechanic" session. I told him my story (see my first post) and his first question was "Do you run at low rpms?" I said, no, usually at 2400. He said that is too low for long periods of time. He said a diesel needs to run hard and recommended to run it wide open, under load, for 5 minutes every hour. This will keep the injectors nice and clean. Any comments about whether this fits other recommendations you've gotten?

 

[Joe2954]

Yes. My 3YM30 WOT is about 3500 rpm. I normally cruise at about 26-2800 but run it up to >3000 for a few minutes every hour if on a long power run. Trouble is I often only run the engine for a few minutes to get out of the slip and get the sails set, then again a few hours later to get back in. However, I try to find opportunities to run WOT or close to.

 

[frankies56]

The mechanic is right a diesel motor does need to run wide open for a little while not just for the injectors but to keep the exhaust clear of soot, but one thing I would recomend is using a good fuel additive to help with lubrisity and keeping exhaust clear also to boost cetane that makes it run better as many fuel companys use little for cetane in there products. also do you use car fuel or agricultural fuel. when you buy fuel does it have a red tint to it or is it clear. car fuels have less lubrisity than the old fuel used in agricultural and more sulfur which is a lubricant. for what ever that is worth. happy sailing

 

[druid]

Yanmar's (older ones anyway) are particularly susceptible to not being driven hard. And it's not just RPM - make sure you run it hard for a while to get the temps really up. I think the fact that most boats here on the West Coast often motor all day is the reason we don't seem to have the problems with clogged mixing elbows that everyone here seems to have.

druid

 

[Jerry Clark H356 SV Persi]

I had a similar problem, but not as severe an RPM loss on a long cruise (KY to FL) a couple of years ago. Coming from Lulu's to Turner across Mobile Bay I opened my throttle to max and discovered that I wasn't maxing out as I had in the past and was getting some vibration. Throughout the entire trip down I had soot on the stern and my fuel consumption was up. I had not until late in the cruise opened my throttle to max RPM. I could only get 3100 Max RPM and was getting soot buildup on the stern and my fuel consumption was higher than normal. My normal max RPM had been around 3400-3500. At Turner I changed injectors and also discovered on haul out in Mobile on the return leg that my MaxProp was worn and needed to be refurbished. I didn't have time to wait for the MaxProp to be refurbished so proceeded on North. When running the 3GM30F, I had for years just set 2750 RPM (around 75 to 80 %) and cruised at 6.2 knots. I returned up the Tenn-Tom at 2500 RPM, had much less soot and although heavily loaded and against a lot of current, the soot and fuel consumption went back down. The MaxProp hasn't been fixed yet and I will haul and do it this year. I have reduced my cruising RPM to 2500 until I get this fixed. I hadn't throttled up to max RPM in years. I would recommend you do so periodically so you can see if changes are occurring. I attributed my soot to being under more loaded conditions because we had both summer and winter clothes, full supplies, 25 gallons go furl on the rail, etc. my speed was down to about 6 knots, not 6.2 and that also I though was due to sitting lower with more drag.

The three things I would consider are injectors, fouled prop and mixing elbow if you develop this condition.