Yanmar 2GM20 Engine Smoke


New member
13 Aug 2014
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Hi, I have a Yanmar 2gm20 in my boat from around 1999. It has never smoked except at max revs, until recently when above a third revs it gives out light grey smoke, getting darker as revs are increased. I read in the Yanmar manual that this could be caused by a clogged exhaust elbow. I removed the exhaust elbow which wasnt blocked, however on inspection, I noticed a tiny pin hole on the inside of the elbow, not the outside, approximately 1 inch from the water inlet, towards the end of the elbow. Would this cause the engine to smoke? Any help would be greatly appreciated, trying to go through a process of elimination before removing injectors etc. My prop is dirty and I will need to clean that, and it is probably contributing to the darker smoke, however I haven't had such an issue before even with a dirty prop. I had the head reconditioned 2 years ago with new valves etc.

Channel Sailor

Active member
5 Mar 2009
Portsmouth (UK)
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Suggest wash or replace the air filter as well. Fouling on the prop and hull bottom will confuse analysing what the problem is so suggest sort that out first. My 2GM20 started smoking with black smoke last year more than it had done in previous years. Noticed it when reving the engine just before shut down after pottering around moorings, a cloud was emitted. It was fixed completely after replacing both the fuel filters, cleaning the airfilter and scraping out the coke in the exhaust manifold (and very carefully around the engine head exhaust port). In very cold winter weather on odd days I once noticed small amount of steam which I reckon is normal as it is looks like condensate.

I recall many years a I once motored a few miles on a small yacht with a very dirty bottom and prop, same model of engine. At high speed it smoked a lot and did not go very fast, felt bogged down. Fixed with a jet wash and new antifoul.