Blue Smoke

[Tim22]

Sorry if this has been covered before. I have gone through many of the old posts, and while there is much discussion about blue smoke none of them seem to replicate my issue.

I have a yanmar 2gm20f with 1065 hours on it and seems to be running well. I have been lax at running it at higher rpm's so today, while at the dock, I decided to gradually work it up to 2800 in neutral. I warmed the engine up for about 10 minutes at 1800 and then gradually increased the speed. All went well until I hit about 2600ish when blue smoke started to come out the exhaust. I continued to 2800 and the smoke continued. As soon as I dropped back down to 2500ish the smoke stopped.

I'd be grateful of any ideas as to what would cause this and more importantly, how to fix it!

Thanks
Tim

 

[Skipper]

This may or may not address your issue, but don't run it with no load. Put it in gear. Just be sure the dock lines are good.

Although you might get a different color smoke under load with the boat unable to move. Best to do these tests in open water.

 

[LittleCreek]

Sorry if this has been covered before. I have gone through many of the old posts, and while there is much discussion about blue smoke none of them seem to replicate my issue.

I have a yanmar 2gm20f with 1065 hours on it and seems to be running well. I have been lax at running it at higher rpm's so today, while at the dock, I decided to gradually work it up to 2800 in neutral. I warmed the engine up for about 10 minutes at 1800 and then gradually increased the speed. All went well until I hit about 2600ish when blue smoke started to come out the exhaust. I continued to 2800 and the smoke continued. As soon as I dropped back down to 2500ish the smoke stopped.

I'd be grateful of any ideas as to what would cause this and more importantly, how to fix it!

Thanks
Tim

2800 rpms with no load? I'm not surprised that you got smoke. No load = no heat.

Diesels need a load on them. The blue smoke you are experiencing is from fuel not being burned completely.

We used to call it wet stacking on Navy Tugs, and it has caused many a stack fire from excessive idling, or idling up the engine for long periods with the prop not being clutched in. Granted, these were large platform 2 stroke Fairbanks Morse engines, but the same theory still applies to most any diesel without computer regulated fuel input for combustion.

80% load is usually the sweet spot for testing diesels.

 

[Benny17441]

I agree that to properly determine the condition of a diesel engine conduct any test with the engine under load at higher RPM. The engine needs to reach operating temperature and the governor needs to sense the load to fully operate as intended. There are three colors of smoke that are associated with these small diesels and those are; white usually denotes steam and is associated with overheating, black denotes unburned fuel and a condition known as overfueling as a result of a fouled propeller or obstructed air intake tube and blueish which denotes crankcase oil being burned which represents worn piston rings or valve guides. I would not attempt to diagnose the condition of one of these engines by what I could observe at idle or an engine not under load. Yanmar engines in particular do not take well to idling at low RPM; if you feel the need to idle the engine for any length of time longer than 5 minutes go ahead and advance the throttle to around 1,000 RPM and let it idle there. Do not shut the engine off after a run and allow it to cool down gradually at a fast idle. Hope that smoke you see with the engine in neutral does not reappear when you run the engine hot and under load.

 

[Tim22]

Thanks for the help. You may be sure that I won't rev the engine up again unless it is under load. I haven't had a chance to try it under load but will be sailing on Wednesday so will try it then.

Thanks
Tim

 

[NYSail]

Smoke is also associated with a clogged mixing elbow. I replaced mine 9 years ago when I bought my boat. Last summer I started noticing faint whitish smoke at higher rpm's and didn't think much of it. Did not think of mixing elbow at all as water flow was still strong and steady. This summer had much more smoke at higher rpm's with still good water flow. I thought injectors, however ended up being clogged mixing elbow..... Only exhaust side. Was 90% blocked but water Channel was perfectly clear which masked the elbow problem for me. Changed the elbow and no smoke.