Merc 850 (85hp)How to check/clear cooling system of items plugging system.

[sailor]

Hi Guys. After reading some of the other posts about mercury cooling/water pump problems I think I have bits and pieces, debris in the cooling system of newly acquired 850 model 85hp 1975 Mercury. The guy I bought it from started it for me on muffs and it seemed to run ok except one carb was leaking fuel. I took it to our local outboard shop and they convinced me the water pump impeller should also be replaced, which was done, the carbs rebuilt, plus the fuel lines renewed, and a general going over. Ran it from the shop home, about 5 miles, and everythig ok. Watched telltale close and had a stream from it all the way. However now in restarting it I get nothing from the telltale except smoke(exhaust). I did get a stream from telltale after I blew it out with air but stream only lasted about 10-15 seconds. I now suspect that there must be something blocking the cooling chambers, although the engine did not seem to overheat but I did not run it more than 2-3minutes as I was concerned with no telltale stream. Assuming there is junk in the cooling system, perhaps from old impeller, that has been stirred up,? what can I do to flush it out to restore telltale stream? Thanks!!!!!!Clark

 

[Chris1956]

Re: Merc 850 (85hp)How to check/clear cooling system of items plugging system.

Sailor, I just returned from vacation, so if noone has answered this, here goes. If you take off the cowling on that motor and start it up on the muffs, there should be water comming out of the grating above the rear of the anti-ventilation plate. It this water is lukewarm, it it pumping correctly. Also some water will exit thru the prop. Pull off the hose from the cylinder to the telltale. Water should stream out of the pipe fitting on the cylinder head. Those teletales clog easily.

 

[clarkm]

Re: Merc 850 (85hp)How to check/clear cooling system of items plugging system.

Thanks to Firstmate for your response. A neighbor today towed me all the way back to a ramp where we were able to get my pontoon out of the waterand back to the shop that replaced the impeller and did the other work on the motor. I am anxious to hear what is causing the lack of water at the telltale and to get it fixed. I am pretty good at mechanics but not very familar with Mercury outboards as yet. I have pretty much always had OMC products. Guess I should have stuck with them if an impeller in a Merc only lasts an hour for a five mile ride.

 

[Merc805]

Re: Merc 850 (85hp)How to check/clear cooling system of items plugging system.

ClarkM<br />I don't think it's the Mercury Impeller that is specifally the problem as they are all made by the same people out of the same rubber.<br />Mine has not been changed for 4 years and is still working...<br />Sounds like remnants left in system ..as you say.