White Smoke

[Gulfislander]

I need some advice. I have a Niagra 31 with a GM20FC Yanmar engine and SD20 saildrive. There is only 350 hours on both. I recently replaced the 2 blade folding Volvo prop with a 3 blade Flex-o-fold. On the first trip I noticed that there is a continuous but small amount of white smoke at cruising rpm's. I spoke with the mechanic at our marina who told me that most boats smoke. This answer did not inspire much confidence so I am reaching out to the boating community for help. Should I be worried?? The book I have on diesel engines speaks about lack of compression, air in fuel lines and unburnt fuel. I cannot see it as an engine problem as it still runs as smoothly as before switching props. I am thinking it has to do with the pitch of the blade...which I have to confess that my understanding of is a bit weak. I had given the manufacturer all the specifications and they had assured me that they supplied other owners of Niagra 31's (same engine and saildrive) with the same prop. Should I be worried? Is their something wrong? Other than this I love this prop...help! Thanks ahead of time.

[Gladrags1]

I can't say about what is causing it but white smoke usually is steam from an overheating engine. Black smoke is unburned fuel and gray is poor compression. How's the engine temp? Have you noticed this smoke prior to prop change? When the yard says "most diesels smoke," that is true. However mostly the color of that smoke would be gray not white.

Hope this helps.

Tod

[JimsCAL]

White smoke can just be water vapor in the exhaust gases condensing. Are you in a location where the water is cold? Does it clear up or reduce as the engine comes up to full operating temperature?

[Faster]

Has there been a noticeable change in boat speed/rpm with the new prop? If so it may be a pitch change issue.

If the 'white smoke' is no longer visible in your wake a few boatlengths aft (on a calm day) then it's likely water vapour. If there's a visible 'haze' behind you then it would truly be smoke. Another think that smokes white is burning antifreeze....

A plugging mixing elbow is another common possibility.

[Gulfislander]

Thanks for the responses. This engine does not have a temp gauge. It only has a temp alarm. I do have more speed with lower rpm's. I use to get 5 knts with 2800 rpm while now I get 6+ with 2500 rpm's.

The white smoke dissipates just a couple of feet from the aft of the boat and we do have quite cold water here in Vancouver. It does not seem to change when the engine come up to temp. It is consistent when under way.

[SlowButSteady]

Sounds like vapor from combustion products. Remember, burning any hydrocarbon produces lots of water vapor. Since the engine is FW cooled the only other way for water to get into the cylinders while running is from the FW cooling loop via a bad head gasket. If the coolant level isn't going down, and you don't appear to have a lot of gas bubbling out of the coolant overflow tank, the engine is probably fine.

[T37Chef]

You may try moving the injector pump timing forward a degree or two. Its easy to do, mark where it is now, loosen, move forward in the direction the arrow shows, tighten, check. Worked for me, got the tip from Buddy at Baltimore Diesel, he's been working on diesels for 50+ Yrs...he knows a thing or two

[Faster]

Sounds like water vapour... the speed change indicates a coarser pitch than before so the engine is working a little harder..