I thought I'd post these pictures of the thermostat from my 15. I've flushed it well after saltwater use but I bought it used, so I didn't know if the previous owner did. The bottom cylinder is getting much hotter than the top one so I suspect the gunk has blocked a coolant passage. I'm going to take the head off to look further. I'm going to try salt-away but I've read a few posts that it really doesn't help.