As long as you have the 2GM20F there are no zinc's in the engine. It seems this question has come up many times before with the same results of some saying that the Yanmar GM series fresh water cooled engine doesn't have zinc's, and others suggesting otherwise. Check out this thread at the bottom of page 1 and top of page 2: (There is no) Zinc pencil on Yanmar 3GM30F
There are other places on the internet that say the same thing, but here are the results:
Yanmar uses cupronickel heat exchangers in all the fresh-water cooled GM series and do NOT need zinc's. Then again just try to buy the zinc for a 2GM20F, you won't find it.
10-11-2009 08:50 PM
The raw water cooled version has zincs in the block. Fresh water cooled version should have a zinc in the heat exchanger.
10-11-2009 05:35 PM
I have the 2GM20 raw water cooled version, 2 zincs. 1 in the block on the dip stick side, just back and above it . The other is on the rear side of the head. They need to be there even in fresh water.
10-11-2009 09:46 AM
I have a 2GM20F as well. There are no engine zinc's for the fresh water engine, but the raw water version has them. The manual covers multiple versions of the engine and was probably refering to the raw water (2GM20) and not the fresh water (2GM20F).
I just signed a Purchase & Sales agreement on a Pearson 28 with a Yanmar 2GM20F, and was looking for similar info. I haven't done a detailed search, but I found a thread on sailboat owners that says only the raw water cooled version (2GM20) has a zinc.
It would be best to locate service manual for an engine with diagrams, showing parts.
However, most likely you have zinc somewhere on a heat exchanger. Iím not familiar with your engine. Just look at the heat exchanger and locate a bolt which makes no sense. It is something sticking on a side without apparent reason. Unscrew it, most likely there is pencil type zinc screwed to inside of this bolt.
I hope someone with knowledge of the engine will prove me wrong
10-10-2009 08:55 PM
Replacing zinc on Yanmar 20M20F
I am new to sailing and own a 2001 Hunter 320. I was reviewing the Owners Manual to the Yanmar 2GM20F and it states you should replace the engine zinc every 300 hours. The manual indicates the cooling system is a "Fresh water cooling with heat exchanger".