I switched to industrial vinegar (10%) and later to muriatic acid. That cleaned things up in a hurry. I actually soaked the old thermostat clean and kept it for a backup. A car thermostat, which doesn't get any build up, is good for decades. Why not an outboard thermostat with the build up dissolved periodically?

I switched to industrial vinegar (10%) and later to muriatic acid. That cleaned things up in a hurry. I actually soaked the old thermostat clean and kept it for a backup. A car thermostat, which doesn't get any build up, is good for decades. Why not an outboard thermostat with the build up dissolved periodically?