Yanmar exhaust color troubleshooting

[Pizzazz]

Just sharing a success story with bad exhaust color on small Yanmar engines. So, I started getting this bad black/brown exhaust color from my Yanmar 2GM20F engine in the last couple of weeks, especially when changing rpms while docking. Everything appeared to be normal. It was really bad, discoloring my stern, etc. I went through the following troubleshooting steps, included here for reference:

Yanmar shop manual, bad exhaust color:

1) Load unsuitable - check propeller, power take off, etc.

2) Fuel injection timing off - adjust injection timing. For this engine, I believe the only way to adjust the time is by adjusting the valve clearance which I had done recently.

3) Fuel unsuitable - unlikely

4) Injection valve faulty - no idea, deemed unlikely

5) Intake/exhaust valves leaking - unlikely, max power achieved

6) Injection pressure too low - unlikely, max output achieved

7) Precombustion chamber melted - unlikely

So, I went back to number 1) and after some head scratching (propeller is clean, turns freely, etc.) decided to check the gearbox oil level. Well, it was completely empty. Filled with oil and the problem went away immediately. I can only imagine how hard it must have been on the gears and the engine with no oil in the gearbox. I hope the gears did not suffer long-term damage.

Lessons learned, sharing for the benefit of the community. Check your oil levels regularly.

SV Pizzazz

[Compass790]

Good on you for admitting your boo boo.
Bit surprised you didn't notice noise or smell or high temp though? Or is your engine in a sound dampened box?
Glad it was only a couple of weeks, hard to say if your gearbox will be ok or not but you definitely would have put a fair bit of wear on it.
I'd change the oil again after a couple of hours as there will be metal particles in it.
Check for leaks as well when gearbox is hot if you can.

[RaymondR]

The most usual cause of leakage from those gear boxes is that there has been corrosion of the output shaft where the seal runs on it. If it is corroded and pitted you can fix it by installing a SS sleeve which are available from bearing supply places.