By the way, I just had to take apart the head on my just bought 1993 25hp Johnson because it was overheating upon my first test in the tank. I test them with a digital infrared thermometer. The engine temperature kept going up and up till I shut it off at 178 degrees. I opened up the head (not an easy quick job if it was used in saltwater as the bolts all lock up and breakoff!) and found it all clogged up. Moreover, the thermostat was locked up and totally clogged, not a drop of water was going out the exhaust everything was just recirculating, hence the temperature kept going up and up.
Anyhow, to get to the point, I discovered that to get to the thermostat and this engine, you have to remove the entire cylinder head cover plate, that's 14 bolts by itself, let alone that you have to remove the coils, power pack, spark plugs and wires and then some, just to get to the plate with it's 14 bolts! CRAZY!!!!
No way I'm going to put in a normal thermostat that may lock up tomorrow if it's defective. This is the ideal situation to use the hatless thermostat, which will never fail! I'm not going through this again. Hopefully my flushing the engine with fresh water will give me some years before I have to go back and clean the heads again, maybe 20 years, as I don't think the prior owners ever did it.
