Greetings,<br /> This is my first year with an I/O style boat and I'm in the midst of trying to debug and fix any future overheat problems. <br />Scenario: I was running on Cayuga Lake, NY with a water temperature around 65-70 degrees, I had been cruising at 3K RPM's and opened the boat up for the last 8-10 minutes before returning to the dock. When I slowed for the marina I noticed a plastic acrid smell. I immediately noted the status of the water and oil gauges which were normal (I'll describe what normal water temp has been in a minute.). I removed the rear engine compartment cover and a considerable amount of smoke that wasn't picked up by the blower came from the compartment, enough I grabbed the fire extinguisher. Very acrid and synthetic smelling, not like oil on a hot manifold. After there was no fire observed I started the engine up and the smoking stopped. Upon cooling I went over the engine for signs of a hose or something getting against the lower exhaust system. I found that a bilge pipe was stuck to the side of the lower exhuast pipe, I pulled it loose, but even though it had stuck as a result of heat, it did not appear to have enough damage to have caused as much smoke as I saw. I inspected the hard rubber exhaust couplers that appeared to be fine with no holes. I unhooked the hose from the lower unit housing and started the engine momentarily, the lower unit pump just gushed water. I hooked it back up and checked the deflection of the belts. They deflected a good inch, so I tightened both to the 1/4" recommended deflection. I then started the boat and used it that afternoon including some skiing. No smoking problems noted. A couple of things do not seem exactly right to me: 1. The temperature gauge then and now barely comes off the peg when the engine is obviously warmed up, maybe<br />1/4 off the coldest point. I noted the voltage at the heat sensor near the thermostat as being 8.5 volts when the engine was completely warmed up. The temperature needle will move within this 1/4 inch range, but that is really not perceptable unless you keep a close eye on it. I'm assuming this voltage varies depending on the water temp.<br />2. I notice that the left exhaust manifold, is noticeably warmer to the touch than the right side. This was also the side that<br />the bilge pipe stuck to. On the front top of the engine a number of hoses come into the thermostat housing, there is some sort of what appears to be a balancing mechanism in the neck, that has a plastic spring loaded ball on each end. Last Fall I changed the thermostat and cleaned the housing out, at that time the spring loaded balls were free and clear. I haven't pulled those hoses off as a result of this incident. I know that the waterpump was changed on the boat the year before I bought it. <br /><br />The loosened belt may indicate why it overheated at high speed, but I'm not certain why the imbalance in temperature between the left and right exhaust manifolds and why the temperature gauge doesn't come up to the 'normal' operating range, even when there was an obvious overheat incident. My thoughts are that the block temperature was normal, but the waterjacket temperature in the manifolds was high causing the rubber couplers to smoke. The boat is a 1986 Empress 200XL with 350 hours on it. Allways run in fresh water. However, the thing that prompted me to change the thermostat during the winter maintenace prep was black mineral build up around the thermostat. Can these types of systems be flushed by running in a inclosed tank of some sort of solution? If anyone has some thoughts on what I've described, they would be appreciated. <br />Thanks in advance. rogmo@attglobal.net
