Hey guys, I've enjoyed reading posts on this forum for the past few months and have gained much knowledge in the process. There's been some discussion regarding diesel engines not performing as they should and I've taken all the posted information on board in an effort to fix my problem, but so far without success. My recently acquired Bene 33.7 (97 model) has a 20hp Volvo which was initially running fine, then (virtually overnight) started misbehaving. From idle to half throttle is fine, smooth running up to around 1500-1800 RPM. But as I increase throttle above 50% the revs don't increase and black smoke/soot spew from the exhaust. From my checks I've confirmed that fuel is clean, prop is clear and free. Someone has suggested it's overfuelling and it's time to call in the mechanic, but I've also heard that the exhaust can (over time) clog up with soot and this could be restricting airflow through the engine and causing the problem. I'll probably check the exhaust this weekend before resorting to the mechanic, but am I wasting my time????
Another diesel question
- Thread starter Blue Heeler
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BH
No direct experience here, but I think you are going in the two right directions: clogged exhaust creating backpressure (this plagued Tania Abei on her circumnavigation) or clogged/poorly performing injectors.
No direct experience here, but I think you are going in the two right directions: clogged exhaust creating backpressure (this plagued Tania Abei on her circumnavigation) or clogged/poorly performing injectors.
exhaust elbow could be te problem
You didn't mention how many hours you have on the engine but it sounds like a clogged elbow and is the easiest thing to check/fix before fooling around with injectors or fuel pumps so I'd start there. Don
You didn't mention how many hours you have on the engine but it sounds like a clogged elbow and is the easiest thing to check/fix before fooling around with injectors or fuel pumps so I'd start there. Don
clogged air filter
may, just may be another cause. As this one is easy to check, perhaps do that first. If not well maintained in the past it could be a combination, though.
may, just may be another cause. As this one is easy to check, perhaps do that first. If not well maintained in the past it could be a combination, though.
fuel return line
If your fuel system has a fuel return line to the tank and it is restricted in any way. It will cause the problem you are having. Easy to check. Trace from tank to engine looking for sharp bents etc.
If your fuel system has a fuel return line to the tank and it is restricted in any way. It will cause the problem you are having. Easy to check. Trace from tank to engine looking for sharp bents etc.
Try running it with no load at the 1500-1800
rpm range for several minutes and then gradually increase the speed. If the engine isn't getting enough air at high rpm I would look to the air cleaner. When you say "overnight" do you mean literally or do you mean from one use to the next? 2 weeks is enough time for Mud Dauber wasps to build a rather large nest. If I din't think it absurd I would believe that there was some sort of a brake on the engine.
rpm range for several minutes and then gradually increase the speed. If the engine isn't getting enough air at high rpm I would look to the air cleaner. When you say "overnight" do you mean literally or do you mean from one use to the next? 2 weeks is enough time for Mud Dauber wasps to build a rather large nest. If I din't think it absurd I would believe that there was some sort of a brake on the engine.
Overfueling?
Replace air filter, fuel filter, clean water separator. Inspect exaust mixing elbow. Add some fuel additive. "Overfueling" is throtling the engine with more fuel than it can burn, hence the black smoke. It is not a mechanical problem in itself but comes as a result of operating an engine with a problem.
Replace air filter, fuel filter, clean water separator. Inspect exaust mixing elbow. Add some fuel additive. "Overfueling" is throtling the engine with more fuel than it can burn, hence the black smoke. It is not a mechanical problem in itself but comes as a result of operating an engine with a problem.
Lots of good info here
although there is perhaps no better way to learn even more details than by obtaining a very good book on the subject. Calder's two books, Boatowner's Manual and Diesel Engines are excellent resources. There are also numerous Internet sources, including this website, BoatUS and your own engine's website (don't know if Volvo has one, but there is a tremendous site for Universals, which include engine and troubleshooting manuals). Good luck, step-by-step. Stu
although there is perhaps no better way to learn even more details than by obtaining a very good book on the subject. Calder's two books, Boatowner's Manual and Diesel Engines are excellent resources. There are also numerous Internet sources, including this website, BoatUS and your own engine's website (don't know if Volvo has one, but there is a tremendous site for Universals, which include engine and troubleshooting manuals). Good luck, step-by-step. Stu
Do you have squirrels?
I had a car come in with the same problem once. We popped the hood took off the air cleaner and started her up. The guy who drove her in confermed it was not running right but no it runs like a champ. So turn it off put the air cleaner back on and close the hood. We went to back it off the lift and it is running like crap again. We went through the hood up air cleaner off drill 4 times before somebody thought "hay it might be the air cleaner". We opened it up to find it completely packed with dog food. Squirrels just stocking up for winter.
I had a car come in with the same problem once. We popped the hood took off the air cleaner and started her up. The guy who drove her in confermed it was not running right but no it runs like a champ. So turn it off put the air cleaner back on and close the hood. We went to back it off the lift and it is running like crap again. We went through the hood up air cleaner off drill 4 times before somebody thought "hay it might be the air cleaner". We opened it up to find it completely packed with dog food. Squirrels just stocking up for winter.
Thanks to all ....
.... for your replies/suggestions. The engine has roughly 600 running hours and the exhaust elbow will be the first thing I'll check this weekend. After that I'll check for fuel return line. As for the other suggestions .... Air filter has been replaced, as has fuel filter and the water separator is clean. Fuel additive to clean injectors hasn't made any difference. By "virtually overnight" I mean from one use to the next (actually 3 days) and we don't have mud dauber wasps down under (thankfully). Also, the keel is clear (checked that when I dove under to check the prop) ...... and no squirrels in oz either (a good yarn though). Thanks again to all .... will let you know what I find ...... cheers
.... for your replies/suggestions. The engine has roughly 600 running hours and the exhaust elbow will be the first thing I'll check this weekend. After that I'll check for fuel return line. As for the other suggestions .... Air filter has been replaced, as has fuel filter and the water separator is clean. Fuel additive to clean injectors hasn't made any difference. By "virtually overnight" I mean from one use to the next (actually 3 days) and we don't have mud dauber wasps down under (thankfully). Also, the keel is clear (checked that when I dove under to check the prop) ...... and no squirrels in oz either (a good yarn though). Thanks again to all .... will let you know what I find ...... cheers
Poor performance
Another possibility can be a faulty thermostat, I had exactly the same problem which only became apparent after about a 30 min run
Another possibility can be a faulty thermostat, I had exactly the same problem which only became apparent after about a 30 min run
FYI
Looks like the problem is a clogged exhaust elbow. It was caked solid with carbon deposit (just about completely blocked) so I've brought it home to try and clear with hammer and assorted small chisels. Hopefully things will be back to normal once I've cleared and refitted. Cheers
Looks like the problem is a clogged exhaust elbow. It was caked solid with carbon deposit (just about completely blocked) so I've brought it home to try and clear with hammer and assorted small chisels. Hopefully things will be back to normal once I've cleared and refitted. Cheers
Elbows
My exhaust elbow has internal water section that eventually will corrode and have access to the engine (Yanmar). Also, when I bought my boat I removed and replaced the elbow as it was also caked with rust and carbon. When I grabbed the peice with a wrench the front caved in....apparently it was paper thin. So be careful and confindent that it is in good condition. For 150 ir was worth changing for me as mine was 20 years old. Yanmar reccomends replacing every 5-10 years I heard.
My exhaust elbow has internal water section that eventually will corrode and have access to the engine (Yanmar). Also, when I bought my boat I removed and replaced the elbow as it was also caked with rust and carbon. When I grabbed the peice with a wrench the front caved in....apparently it was paper thin. So be careful and confindent that it is in good condition. For 150 ir was worth changing for me as mine was 20 years old. Yanmar reccomends replacing every 5-10 years I heard.
Cause and Effect
Well, after further investigation I've discovered that the exhaust mixing elbow on my volvo engine is also divided into two sections, essentially one pipe inside another, the inner being exhaust and the outer for water discharge, with the separate flows coming together just before the elbow connects to the exhaust hose. Sections of the inner pipe wall had become badly corroded which resulted in the top inner portion breaking away and wedging itself down across the exhaust elbow outlet, thus restricting the exhaust and allowing carbon to start building up, eventually completely blocking the elbow. Although it cleaned up ok, I will need to replace the elbow because of the badly corroded and broken inner pipe, as it now wouldn't prevent back-flow of water into the exhaust manifold. I'm assuming this will be the first replacement in it's nine year life, so Yanmar's recommendation of 5-10 years seems about right. Check your elbows people
Well, after further investigation I've discovered that the exhaust mixing elbow on my volvo engine is also divided into two sections, essentially one pipe inside another, the inner being exhaust and the outer for water discharge, with the separate flows coming together just before the elbow connects to the exhaust hose. Sections of the inner pipe wall had become badly corroded which resulted in the top inner portion breaking away and wedging itself down across the exhaust elbow outlet, thus restricting the exhaust and allowing carbon to start building up, eventually completely blocking the elbow. Although it cleaned up ok, I will need to replace the elbow because of the badly corroded and broken inner pipe, as it now wouldn't prevent back-flow of water into the exhaust manifold. I'm assuming this will be the first replacement in it's nine year life, so Yanmar's recommendation of 5-10 years seems about right. Check your elbows people
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