Heads up 75,90,115 Merc and Yamaha owners

Santiago - 9-15-2023 at 12:36 PM

Doing our 3 year tune-up, when we drained the oil it came out milky. Ugh.
Was running fine. Compression check was 190 all 4 so no blown head gasket. Shop said to check the thermostat - it was stuck open. They said not uncommon on these blocks, Yamaha was making the blocks for Merc up till a few years ago. The oil never gets hot enough to burn off the natural condensation so water builds up in the oil. Thermo is supposed to close at 140 degrees.
All good now but good to know if you're in Baja doing your own maintenance.