I had the same problem on 115 4 stroke Merc. He said their is a rubber bushing where the water from the pump goes up to the block. This can get hard or damaged. Not sure on a Yamaha. IMP Poor design!
Drained the oil in my Yamaha 115 4 stroke and it looked like chocolate milk. I guess water in getting in the oil. I was told the head gasket was the only way for it to get in. Are there any other ways, other than a cracked block or head?
Getting a compression tester to check that this weekend.
I had the same problem on 115 4 stroke Merc. He said their is a rubber bushing where the water from the pump goes up to the block. This can get hard or damaged. Not sure on a Yamaha. IMP Poor design!