We're spending the day with the service gurus at Norfolk Marine talking about some maintenance issues, and one we haven't touched on yet is how to change the thermostat on an outboard engine. This is a stuck thermostat. Chris, how do I even know if my thermostat is stuck in the first place?


Chris Breeden, Service Manager/Yamaha Master Tech: Well, one of the easiest signs is you get a high idle and oil dilution. The oil dilution is going to be fuel finding its way past the rings and getting into the oil.

Lenny: Oh, when your engine is "making oil".

Chris: That's it.

Lenny: Well, can you show us how to change the thermostat?

Chris: Sure can. First thing, just pop the cowling off, set it aside, and on this model there's a flywheel cover, it pops right off, and on the 150's (Yamaha F-150 four-stroke outboard) it's located right here on the side. Take your ratchet with a 10mm, pop these guys loose, and with all three bolts out we can get the cover out of the way. Then it comes right out.

Lenny: That's what a new thermostat looks like, and there's an old one.

Chris: That's what they're supposed to look like when they're cold, completely closed.

Lenny: On every model engine the thermostat will be located in a different place, right? How do I know where to find it?

Chris: The easiest way is to refer back to the service manual, and if you don't have the service manual you can go on the internet and Google, and find it there.

Lenny: So just about all of these service manuals, you can find on the internet?

Chris: I haven't found one yet that you couldn't.