I hoping someone can tell me I dont have a big job in front of me. I just bought a 31 hunter with a 13hp 2gm yanmar(closed cooling system), last weekend we went for our first overnight trip it was great.. on the way back there was no wind so we motored back about 40 miles. about half way back i thought id see what the hull speed was (we had been cruising at 2000rpm 6mph)and brought it up to about 3400rpm and 7.5 mph. All seemed fine until I looked at the back of the boat and noticed oil spots all over that were not there before. So I reved it up again.... There was some smoke and more oil... So I cleaned off the back of the boat and kept the rpm around 2000 and had no oil or smoke. No other problems.. no noticable use of oil on the dip stick. Is this normal for diesel? Or do I need rings and a valve job, Yuck! The boat belonged to a little old man from detroit who was the only owner and hardly used it wich I verified! Please someone out there tell me Im not doing something that you only have todo to diesels. ps no oil in the air filter
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probably over proped.
You boat is probably a little over proped. You do not want to operate this engine a that low RPM's for extended periods of time. It will cause your cylinders to glaze and the elbow to coke up. The optimal operating range is from 2500-2900 rpm for extended periods. I think you probably have a 15 x 12 prop. I found that this is slightly more pitch than what worked well for our engine. I believe that a 15 x 10 would be just about correct. You should check with a prop shop for a professional opinion. Our H'31 will also belch black soot if we operate at that high level of RPM. It will also cause to to overheat too. Just try running your engine at 70-80% of the max rated RPM (3600). Change the oil, filters, and your engine will outlast the boat.
You boat is probably a little over proped. You do not want to operate this engine a that low RPM's for extended periods of time. It will cause your cylinders to glaze and the elbow to coke up. The optimal operating range is from 2500-2900 rpm for extended periods. I think you probably have a 15 x 12 prop. I found that this is slightly more pitch than what worked well for our engine. I believe that a 15 x 10 would be just about correct. You should check with a prop shop for a professional opinion. Our H'31 will also belch black soot if we operate at that high level of RPM. It will also cause to to overheat too. Just try running your engine at 70-80% of the max rated RPM (3600). Change the oil, filters, and your engine will outlast the boat.
diesel smoke
The black smoke you see and resulting black soot you see on your stern, in a following wind especially, is the result of trying to put too much diesel fuel into your engine in an attempt to get it to turn higher revolutions than it possibly can under current conditions. Watch the diesel trucks or buses on the highways, ever notice how much soot they put out when they really step on the throttle, it's unburned diesel fuel and usually lets up once they reach a speed at which the engine can burn all the fuel that's being put into it. Your boat has reached it's potential hull speed, be happy! I know the first time it happened to us I thought something was wrong with my engine as well, backing off on the throttle until the smoke clears is the answer. Your engine will run forever without work if you just change the oil and filter regularly. I've seen large overloaded power boats trying to get up on a plane leaving a trail of black soot for miles in a calm wind. My last piece of evidence was the weekend I let my son-in-law take our 33' out for a day and found the stern covered with black soot after he tried to turn it into a speed boat. As I said earlier BE HAPPY, you've got great hull speed for the size of your boat.
The black smoke you see and resulting black soot you see on your stern, in a following wind especially, is the result of trying to put too much diesel fuel into your engine in an attempt to get it to turn higher revolutions than it possibly can under current conditions. Watch the diesel trucks or buses on the highways, ever notice how much soot they put out when they really step on the throttle, it's unburned diesel fuel and usually lets up once they reach a speed at which the engine can burn all the fuel that's being put into it. Your boat has reached it's potential hull speed, be happy! I know the first time it happened to us I thought something was wrong with my engine as well, backing off on the throttle until the smoke clears is the answer. Your engine will run forever without work if you just change the oil and filter regularly. I've seen large overloaded power boats trying to get up on a plane leaving a trail of black soot for miles in a calm wind. My last piece of evidence was the weekend I let my son-in-law take our 33' out for a day and found the stern covered with black soot after he tried to turn it into a speed boat. As I said earlier BE HAPPY, you've got great hull speed for the size of your boat.
C
Chris
thanks Richard and Steve
Thanks Richard and Steve, Before I starts celebrating I just want to make sure that the soot(or unburned diesel) your talking about looks like oil on the stern. I had to use laundry soap to get it off. If the cylinder walls are glazed will running the motor at a high rpm for exteded amounts of time break up the glaze? or do you have to hone the cylinders? It does have a giant 3 blade prop on it, wich sounds like the reason for my low rpm. and heavy drag on the motor but when I increase the throttle the rpm comes right up. what weight oil should I be using, Im on lake superior in the cold land... Thanks again, Im sure Ill sleep better What weight oil should I be using
Thanks Richard and Steve, Before I starts celebrating I just want to make sure that the soot(or unburned diesel) your talking about looks like oil on the stern. I had to use laundry soap to get it off. If the cylinder walls are glazed will running the motor at a high rpm for exteded amounts of time break up the glaze? or do you have to hone the cylinders? It does have a giant 3 blade prop on it, wich sounds like the reason for my low rpm. and heavy drag on the motor but when I increase the throttle the rpm comes right up. what weight oil should I be using, Im on lake superior in the cold land... Thanks again, Im sure Ill sleep better What weight oil should I be using
Check The mixing elbo
When I cleaned out my mixing elbo on my 2001 2gm20 it ran at higher rpm's with a lot less black smoke and higher hull speed,I very rarely get any smoke. I will be cleaning the mixing elbo every year because it made such a great inprovement in performance. nick
When I cleaned out my mixing elbo on my 2001 2gm20 it ran at higher rpm's with a lot less black smoke and higher hull speed,I very rarely get any smoke. I will be cleaning the mixing elbo every year because it made such a great inprovement in performance. nick
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