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Old 30-03-2016, 12:32   #1
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Film On Water From Diesel Exhaust

Question. I have an old Volvo MD6A. No idea how many hours, but it always cranks right up, always, and will run all day long. Never any problems. I'm getting a fuel/oil (don't know which) film on the water from the exhaust. Engine doesn't smoke inordinately, meaning very little. Had the injectors checked, thinking maybe too much fuel going through the engine, which may still be a possibility. Anyway, trying to decide if there may be something relatively simple causing this, before pulling an engine. BTW, doesn't seem to do it all the time, though maybe I just can't see it at times. Obviously, this oil has to be coming through the exhaust, then washed on out with the salt water cooling, unless oil is getting into the heat exchanger somehow. Anyway, looking for some ideas that might point me to a problem. Thanks.
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Old 30-03-2016, 12:49   #2
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Re: film on water from diesel exhaust

I may have misunderstood, but you're thinking of pulling the engine because of this?

It's normal.
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Old 30-03-2016, 13:01   #3
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Re: film on water from diesel exhaust

There will always be a little unburnt diesel oil with the exhaust gasses - Perfectly normal.
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Old 30-03-2016, 13:24   #4
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Re: film on water from diesel exhaust

I was considering a rebuild. Mainly because I'm up from the Gulf on two pristine rivers, the Wakulla and St Marks. Not sure how FWC would react if following me out of the river. Sounds encouraging though, and appreciate the input. I've tried watching other boats at the dock that may be running there engines, haven't noticed the oil from them.
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Old 30-03-2016, 13:54   #5
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Re: Film On Water From Diesel Exhaust

Does it only happen during certain conditions such as at idle or when engine is warm? If not when at normal cruising power I wouldn't get excited about it.
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Old 30-03-2016, 14:19   #6
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Re: Film On Water From Diesel Exhaust

I haven't discerned if there are certain conditions. Lately I've been working on trying to track down the problem, if there is one, and have been running it both in neutral at varying speeds, and under power both forward and reverse. Sometimes it's there and obvious, other times I don't see it. Most of these, lately, are on a cold engine. Actually, I put a new thermostat in the other day because this engine runs cold all the time. Still does with a 160 thermostat in it. Freshwater cooled with a raw water heat exchanger.
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Old 30-03-2016, 16:37   #7
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Re: Film On Water From Diesel Exhaust

Does the engine use oil? I mean after 25-50 hrs do you have to add a half quart or more? Could be just normal wear, piston rings, valve seals or a combination of both. Think the law says that if there is an iridescent sheen on the water, you're liable...I've seen a lot of spray bottles filled with dishwashing liquid and water around...
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Old 30-03-2016, 17:17   #8
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Re: Film On Water From Diesel Exhaust

You might consider putting an inexpensive pyrometer at the exhaust manifold (as close to the actual manifold as you can do it is way before the water injection point) because then you'll know if your engine is running in the right temperature range. This can tell you a lot about properly loading the engine. We watch the pyrometer temp more than rpm on our engine.


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Old 30-03-2016, 17:30   #9
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Re: Film On Water From Diesel Exhaust

Quote:
Originally Posted by jag39 View Post
I haven't discerned if there are certain conditions. Lately I've been working on trying to track down the problem, if there is one, and have been running it both in neutral at varying speeds, and under power both forward and reverse. Sometimes it's there and obvious, other times I don't see it. Most of these, lately, are on a cold engine. Actually, I put a new thermostat in the other day because this engine runs cold all the time. Still does with a 160 thermostat in it. Freshwater cooled with a raw water heat exchanger.
Shouldn't it have a 180 degree thermostat?

Mine lets a bit of unburned diesel through. I wouldn't be spending thousands of dollars on a rebuild because of it though.

You might want to have your injectors tested or even rebuilt. That's a likely place to start.
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Old 31-03-2016, 09:27   #10
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Re: Film On Water From Diesel Exhaust

My previous boat's Yanmar 2GM20F was dripping a small amount of oil out the exhaust, not enough to lower the level just leaving a bit of a sheen...
Could not figure out why/how until I noticed that it was actually dripping out the propane locker lower ru-hull adjacent to the exhaust. That locker (1 of 2) was just used for storage... like extra engine oil and 2-stroke oil for the dinghy... one bottle of which developed a small crack.
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Old 31-03-2016, 09:28   #11
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Re: Film On Water From Diesel Exhaust

Thanks everyone for the input. Injectors have been checked. Seriously thinking of adding the pyrometer, since it was indispensable in my semi trucks, when I had a trucking company.

From all the input, thinking I will just let it ride for now, and keep a watch on it. I'm also going to try and see what other boats are kicking out, when the opportunity arises.

Again, thanks! The suggestions have been a big help.
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Old 31-03-2016, 09:30   #12
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Re: Film On Water From Diesel Exhaust

They all do that but I started putting biobor MD in my fuel. Made a big difference. No more soot on the back of the boat. Well worth it.
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Old 31-03-2016, 10:15   #13
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Re: Film On Water From Diesel Exhaust

You can discuss this with a diesel mechanic, but the engines are actually designed in such a way that they must pass some diesel through. The bigger the engine, the more you would see, especially at idle in calm water. Google Tier 3 Marine Diesel and you can find out what the EPA is doing. Most manufacturers are going to computer controlled injectors to better manage fuel burn, reducing emissions. However, there is debate about the reliability of computerized solutions vs the old mechanical method. I think you would need to buy a new engine to see significant reduction in fuel from your exhaust, but it would still not be total elimination.

Good luck though, we all like a clean environment!
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Old 31-03-2016, 10:25   #14
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Re: Film On Water From Diesel Exhaust

At what point is an oily film on the water a violation of EPA rules for no discharge? Just asking,,
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Old 31-03-2016, 10:32   #15
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Re: Film On Water From Diesel Exhaust

Pyrometers is a good idea, but sounds like your engine is still running too cool. That is the biggest factor in fuel carryover. Why the 260 t-stat?
Also avoid running unloaded.
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