cooling system

[patricklehane]

hi, i have an old mercury 500 outboard, it starts first time and is a great engine, but it only pumps water at high revs, i have had the impellers changed, but have been told that the water pipes have corroded through not being flushed, i have also been told that it would not be economical for me to pay a mechanic to clean the pipes. but i have the time to do this job, but not the money to buy a new outboard, has anyone had any experience with this? if so any tips would be very much appreciated. also does anyone know where i can get a workshop manual from? thanks very much

 

[jfm]

To get at the lower part of the water pipe, remove the gearbox, or "lower unit" as mercury call it. You will be able to clean out or replace the vertical pipe in the engine leg

That is also how you get access to the water pump and impeller (there's only one impeller)

If the corrosion is inside the cast aluminium waterways inside the engine powerhead, it will get more difficult. you can remove various plates in the powerhead to get some access and you'll need new gaskets probably

How do you know it is only pumping at high revs? Symptoms? Does it overheat at low revs or are you just going by the telltale? The telltale might just be a bit blocked - shove some piano wire up it or take it off and replace the rubber pipe. What's the cooling water dsicharge flowrate through the exhaust like when you run it on bellows? And what temperature is the spent cooling water? It should be perhaps 60-70deg C at the telltale, ie like a hot water tap in your house. Not too hot to hold your hand in it. If it's the right temperature, it is maybe pumping/circulating ok

Mercury do an expensive workshop manual but there are various cheaper aftermarket manuals for that engine, just google. You can order from here, and they have a good forum www.oldmercs.com.. Consider buying a parts list rahter than a manual, or as well as. The parts list has exploded diagrams of the engine and is sometimes more useful, when you just want to see how stuff fits together. Mercury parts list can be ordered on the website

 

[patricklehane]

hi, thanks for the help, it is much appreciated. i have investigated further and had an experts opinion, and unfortunately we found out that the corrosion is in the powerhead, i have ordered a gasket set off oldmercs. do you have any tips on taking the powerhead apart etc?
thanks very much