Yanmar 3 GM 30 F works for a minute and then dies

[Gennady22]

Hi all!

We have this problem: when we start our Yanmar 3 GM 30 F engine, it runs for a minute, and then dies down. Moreover, there is a thick black soot coming out of the exhaust, while before it was clean water. When a mechanic came over today, he said that air must be getting somewhere, but he was not able to understand where. He did change the 2 fuel filters - the large one and the small one, on the engine.

Hope someone can help me understand this problem.

Thank you.

[Wotname]

Do the simple stuff first!

1. Remove and check the exhaust mixing elbow. It is very likely to be restricted due to low load operation.

2. Remove fuel tank cap to ensure there is no vacuum forming in the tank due to blocked breather.

If these are OK, we can move on to other possible issues.

[Gennady22]

Please, explain to a new guy how to remove the exhaust mixing elbow on the engine. Also, which fule tank cap do you mean: the one where I pour the diesel? Thanks for answer.

[cram]

Was this a sudden change or gradual change? If gradual, do as above (yes, the fuel fill cap). If sudden, call a mechanic and don't mess with it!

[Wotname]

Originally Posted by Gennady22

Please, explain to a new guy how to remove the exhaust mixing elbow on the engine. Also, which fule tank cap do you mean: the one where I pour the diesel? Thanks for answer.

Yes, the cap where you pour the diesel when filling the tank.

There are two possible mixing elbows fitted to the 3GM30F - standard and U type. The removal of either is similar, see pictures.

[Gennady22]

Originally Posted by cram

Was this a sudden change or gradual change? If gradual, do as above (yes, the fuel fill cap). If sudden, call a mechanic and don't mess with it!

Can somebody recommend a good mechanic around Sheepsheadbay, Brooklyn, New York? Yesterday, I called one, paid him, he changed the filters, and said he is a "generalist", that there must be somewhere that the air gets in and shuts down the system, and after that he said he really doesn't know.

[Gennady22]

Problem fixed. It was the exhaust elbow, with a lot of soot. Cleaned with a BBQ grill cleaner (Easy Off, for example).
https://youtu.be/ancnhJC6lns?si=yGLgd0XsvW_LAvZW

[NorthCoastJoe]

I have a Yanmar 3GM30F in my Pearson now for 8 years. When we shut down we run it WOT for about 30-60 seconds then slowly return to idle to blow out any crud from the low RPM used in the marina. I have never had the exhaust elbow get plugged up. I just had it off for a look this summer, the only area that had any build up was the fitting where the water is injected. Otherwise very clean.

[Wotname]

Originally Posted by Gennady22

Problem fixed. It was the exhaust elbow, with a lot of soot. Cleaned with a BBQ grill cleaner (Easy Off, for example).
https://youtu.be/ancnhJC6lns?si=yGLgd0XsvW_LAvZW

Good outcome, thanks for letting us know.