Re: Poppet and Thermostat Question
For many years Merc went without thermostats. I had an '89 tower that had none (not designed into the engine). Don't remember when thermostats were introduced into the lower hp engines.<br /><br />I recently bought an '02, 3 cyl, 90 and the thermostat stuck closed. I threw it away based upon the logic mentioned above.<br /><br />That proved to be the wrong thing to do. Your '89 can probably get by without it, but the EPA posted restrictions on outboards in the late '90's or so and they are running much leaner now. <br /><br />In short, I had to put a new stat back in the engine to get it to operate properly in 75 degree water.....symptoms were rough idle, hard starting, hard restarting after stopping off at a fishing hole, and hesitation getting up on plane.<br /><br />Others on here mention that by allowing the engine to run cool you increase the opportunity for sludge buildup, which I agree.<br /><br />Others mention that if you let water run through the powerhead too fast the waterjackets won't fill up and the top cylinder will run hot and be damaged from lack of cooling, and I agree this could happen too, although I have not researched the process. I understand what they are saying, I just don't have any quantity numbers.<br /><br />Maybe if you leave it out you could run some SeaFoam in your fuel to keep your carbon and sludge flushed out. But that wouldn't address possible damage to the top cylinder from overheating.<br /><br />Your previous owner may have had problems and just chunked them rather than replace them. Now that I am "reformed" I think I'd put them back in. You can get the parts on this site.<br /><br />Mark
