This post is more informational than a question. I have had a long standing overheating problem that, I think, I finally fixed. You be the judge. I'm a novice here, and I might have done more harm than good.<br /><br />I got my yamaha 9.9hp 4stroke when I bought my sailboat. Since day one I had problems with cooling flow. <br /><br />Let me tell you right now that I don't - can't - perform the proper maintenance on the cooling system. That is, flushing the cooling system with fresh water after each use in salt water. I keep the boat on the intracoastal in florida ( brackinsh water) and mostly sail out on the ocean. There is just no access to free flowing fresh water. <br /><br />My first approach to the water flow problem was to shove a piece of wire down the outlet nozzle to clear whatever salt or sand deposits had accrued. Though this worked from time to time, I still experienced overheating while running the engine for extended periods while there was a coolant flow. <br /><br />Next I bought a shop manual and the rebuild kit for the water pump. Though the rebuild is no big adventure the task was tiresome because I had to pull the engine from the boat while it was moored asea( i.e. in the intracoastal). The removal and reinstall from the dinghy was no picnic. This did not solve the problem though.<br /><br />Feeling that I better leave the issue to experts, I pulling the outboard again and brought in to my local yamaha repair shop. I told them the problem and said "fix it". "No questions, no consultations, no money concerns, just make it work." And so they said they solved the problem by replacing a siezed thermostat. Feeling relieved that I could now puttter about whithout worry of the dreaded steam show, I happily ferried the engine out to the boat and installed it anew. Thirty minutes under power later, I pushed the red button in disgust. <br /><br />From here I was purplexed and kept all further motoring down to the small amout of time it took to pass under briges without sail. <br /><br />I month or so later I had a breakthough - or so I thought. While motoring, coolant had stopped, but water was falling from the cowling. I pulled the cover to take a look and saw that the coolant hose from the one of the cylinders had pulled free from the t connector. Inspecting the plastic connector, I saw a large piece of grit lodged in place. Could this have been the problem all along? <br />As I removed the blockage, I discovered a more sinister problem. The plastic t connector linking coolant outflow from the two cylinders had formed a bubble of melted plastic inside its diameter thus constricting flow in general. Perfect I thought! If this blockage was not causing debris to build up, it was at least slowing flow to the point that proper cooling was not taking place. I had finally found the problem. So I cut the bubble out and looked forward to relief from the ongoing overheating problem. <br /><br />Needless to say, this did not solve my problem.<br /><br />I returned to the yamaha shop to deride them about their horrible products. "What kind of outboard can't be used in water without being cleaned after every use?" I asked. <br />Well salt water is different, they replied. <br />Yeah, but we are in florida, and its all salt water atround here. Isn't there some sort of coolant system flush I can use? <br />None worth trying, they concluded.<br /><br />I bought head gaskets from them so I could pull it all open and maually clean the coolant passage in the engine block. I returned to the boat and sat defeated after I realized that I could remove all but one of the necessary bolts to perfom the procedure. I had no desire to pull the engine and bring it home to perform the surgery. "there's got to be a better way", I thought.<br /><br />And here is where it all pays off. I remembered that I had this really caustic hull cleaner down below. Bottle said it disolved barnacles and most all else. Pour it on and rinse away. What the hell. I had two choices - shoot the damn thing and put it out of its misery or pour acid down its throat.<br /><br />And so I did. And you would not believe what came foaming back out of the coolant tubes. I poured some down and waited for the foaming action and then started the engine to rinse it all out. One cylinder had flow and the other barely tricked water at all. I repeated this action four or five times afraid that letting the acid sit too long undiluted in the engine would cause permenant harm. With each dousing and restart, coolant flow increased. By the final time coolant, was jetting five feet out from each cylinder.<br /><br />I have run the engine now at least ten hours since this fix. Each time the engine ran at least two full hours at wot without any sign of overheating or loss of coolant flow. <br /><br />Did I do any harm? I don't know. I'm just damn happy to be able to use the darn thing without having it overheat on me while I'm coming through an inlet or under a bridge.
