[Jonathan Morley]

I have a Mercury 50 - Serial No: 9292974I do not know age, however it is overheating and nu=ot pumping water. I have checked the pee hole which is clear. Does this outboard have a thermostat? Doea anybody know where it is on the engine so I can test/replace it? help!?

[Solittle]

I suggest that you get a manual as you will not be able to do much without it. You could also hit your library as most have outboard manuals. Also use the Search function at the top of the page. Enter "mercury water pump (or thermostat)." There are a slug of posts with tips for you.

[tmcalavy]

Wentworth,With a 9****** serial number, your Merc is probably from the 80's. Mine is a 73-74 and its a 3******. Mine has no thermostat, but not sure about yours. I would bet the water pump impeller in your outboard is toast. Time to replace it. You can find a good Merc service manual on Ebay for not a lot of $$$...they are superior to aftermarket manuals like Seloc or Clymers.To change the impeller, you will have to drop the lower unit off the outboard. Here's how:1.) Put the outboad in neutral at the control box (throttle& shift lever by drivers seat) Raise the outboard up, in traveling/trailering position.2.) Remove the prop3.) Remove the trim tab (the shark fin above the prop)4.) Remove the nut from the bolt that is in the trim tab cavity.5.) Remove the nut from the bolt that is behind the trim tab cavity.6.) Have someone hold onto the cavitation plate while you remove the two nuts that you can see on either side and above the cavitation plate.7.) Now everything from the cavitation plate on down will slide down/off as one unit. 8.) Look at the base of the long driveshaft, there is a housing surrounding the driveshaft that should be held on with 2 or 3 nuts. Remove these nuts, pull the housing up off the driveshaft and check the impeller. The impeller looks like a rubber pinwheel with several rubber blades.9.) The impeller also fits on the driveshaft. Pull the old one up and off and put a new one on. Put the housing you took off back on. Gently push the housing down against the impeller as someone turns the driveshaft clockwise. You want the impeller vanes to bend counterclockwise so the impeller fits back into the housing you are re-installing. 10.) Bolt the housing back down and put the lower unit back on the outboard leg (Reverse the order of removal)11.) It may take more than one try to get the Lower unit back up correctly...just takes patience.12.) You'll know its back on correctly if the prop spins freely in either direction when in neutral, ratchets clockwise when in forward, and turns only counterclockwise under some force when its in reverse.Sounds intimidating, but its not. Impellers should be replaced every other year if you run only in fresh water, and every year if you run in salt water. Have fun or pay to have it done!

[Leaky Tiki]

Tim MCI have a 1978 50 horse merc. It came apart exactly as you said. The impeller is in tact just missing a corner off of 1 blade. I am going to replace it anyway just not sure why, if my impeller was functional, that no water came out the pee hole? I tried poking it........oh well Ill let ya know when its all back together , the guy just called and my parts are in........ Tight Lines