No matter if you boat in salt or freshwater, your outboard water passages can become compromised by, calcium, lime, corrosion, salt, and possibly even some bio growth. What product do you use and does it seem to work for you? Many have tried products like, Rydlyme, white vinegar, CLR, Lime away, Salt Away, Simple Green, Dawn, even caustics like acids. Some can be bad for aluminum, not to mention gaskets seals, o-rings and impellers. What do you recommend and do you flush with muffs with a solution mixer, or run engine in a large water tub mixture? Thanks

No chemicals.  This is all I do.

 

 

Yep, just hook the garden hose up and let the fresh water do its thing. Never had need for anything else.

Sorry should have been a bit more clear. I have a much older outboard and I was not the original owner. I am not sure how well it was maintained and if it was flushed regularly. I do get some overheating from time to time. I have replaced Thermostats and water pump and done the usual maintenance things. I think if I could flush the water passages with a good cleaner I may get it to run a bit cooler. So any ideas on a flush mixture?, I really do not want to remove heads to clean it out manually, because with an older engine that may have been run in salt water, it would be too easy to break a head bolt off inside.

Most cleaners that are alkaline or acidic can attack aluminum alloys causing catastrophic corrosion if not rinsed with distilled water and air dried. Your best bet is running the engine in fresh water. 

Tom

I've owned this old Merc since 2001...serial numbers show it was built in 1974. 

 

Only thing I have ever done to it is replace spark plugs, and the water pump last summer. I always remove fuel line and run it dry before loading on my trailer.

 

Mine had issues pumping water for years. Changed the pump and same problem. Turns out the intake tube, like a short PVC looking thing, was cocked slightly sideways.  It was very tricky to get just right when putting the lower unit back on