I have been under the impression I had a 2GM20(f) (because thats the manual I got with the boat from the PO) and now I think I have a 2GM20 (because I bought a part that didn't fit, and finally looked at the ID plate on the engine (DUH!). I looked at the manual again and it only confused me more. I think the (f) is for freshwater, but can someone explain the difference. My engine is raw water cooled, and I can tell you the water pump shaft on the (f) is larger, as the bearings I bought (thinking it was an (f)) were too large for my pump. Anyway, whats the difference?