Hi folks, I just joined here as I heard this is the place to go with outboard problems.<br /><br />I have a 2000 Mercury BigFoot 50HP 4-stroke (before EFI) Serial # 0T071106 and I have been having overheat problems for several months now. The motor ran flawlessly for years before that and asides from the overheat problem, it still runs well now.<br /><br />When it first started overheating, I did the obvious and pulled the lower unit and put a new impellor in. It was the original impellor that came out, looked as good as the new one. In the 5 times I have dropped the lower unit since then, I have replaced all the water pump parts including the connector hose and water pump body. I have tried 2 brand new impellors.<br /><br />After the problem persisted, I replaced the thermostat. Before putting in the new one, I put it in some hot water with a thermometer and verified that it was opening at the right temperature. Both the old and the new thermostats work perfectly.<br /><br />I have also taken off the water jacket cover and everything in there was clean. I forced compressed air and pressurized water in through all the openings I observed and did not find any problem. Except that a small amount of water comes out of the copper tube where the water pump connects too. I blew high pressure water backwards through the system and got what appeared to be a partial clog out. I never saw anything come out per se, but now the water was flowing much better and I no longer overheat on the flusher, but it still does not flow as well as I think it should and it still does overheat under load. when I backflush it with the lower unit off, most water comes out around the exhaust pipe. Much less comes out of the copper input tube, it is more than a trickle but less than the gusher I would expect out of the tube (must be about half inch in diameter, maybe 5/8).<br /><br />Also, when I force water up the copper input tube, there seems to be a lot more backpressure than I would expect. With full house pressure and holding a hose onto it very tightly, I can force water to go through the system, but I don't think I should have to hold the hose so tightly. When I run the motor with the ear muff flusher, I get a much better stream than with the motor in the water. The water dribbles out even with the new water pump. The flusher appears to mask my problem.<br /><br />My best guess at this point is that I have a partially obstructed water tube, or the area where the water tube connects to the powerhead. So far, I have only tried to ream it with weed wacker line but that is not very rigid. My question is whether I should drop the lower unit one more time and see if I can ream the water tube with something more rigid, like a coat hanger for example. If that doesn't solve it, seems like the powerhead may have to come off.<br /><br />Any ideas or advice out there?<br /><br />You can see even more details of this problem at the boat BB where I have been originally posting about it and folks have been trying to help.<br /> here is the web page link <br /><br />Thanks in advance for any comments.
<br /><br />I have started suspecting air leaks under the water pump. Today, I hooked up the flusher muffs to the detached L/U and pushed water into the pump. Water was clearly coming out between the base and wear plate. On closer observation, the WP base is pitted and may even have a crack in the area where the water comes up from the input holes. Seems like this may explain my less than satisfactory water pump performance with 3 good impellers.<br /><br />So, my next move is to replace the water pump base and then use gasket sealer even though the Clymer says its not needed. Hopefully, this is going to fix it once and for all (or at least another 5 years or so). Looks like salt water eats up the base after a while.<br /><br />One more question, seeing as I have never done a water pump base/oil seals before, can I get away without draining my (3 hour old) gearcase lube out and doing a pressure test when I put the new seals in? A Merc mechanic said this should be possible but I'd like a second opinion from someone who has done it. I have the L/U mounted in a shop vise and have the water pump base completely level and ready for surgery.
