mercury 25hp bigfoot overheating

[hotwater]

I have 2 (1999) on an oceangoing catamaran. it is not easy to freswater flush them and once a year or so i have to pull them apart and clean the cooling system to stop them overheating. The waterflow decreases slowly until the engine overheats and the alarm goes off. It appears that the buildup is around the grommet at the base of the block. <br />Does anyone have a method of preventing the buildup other than flushing? Is there something i can use to flush out or disolve the salt buildup without having to dismantle the thing?<br />Are there things I should check besides the thermostat and impeller in an overheat problem with this engine?

 

[DHPMARINE]

Re: mercury 25hp bigfoot overheating

I'd look close at a failed grommet.Obviously it is restricting water supply.Has the I.D.decreased because of corrosion or heat?Or has the O.D.corroded until the grommet stops the supply?<br /> If the O.D. is the problem,install the next grommet with lots of water-proof grease.<br />DHP

 

[hotwater]

Re: mercury 25hp bigfoot overheating

Thanks for the reply. I've done the job now. On one of them anyway.<br />There is a dog leg on the water supply immediately above the grommet. This little channel was clogged with lots of buildup and restricting the water flow. <br />Corrosion was also a factor.You are right, the corrosion around the grommet had reduced the ID and is the first restriction after the impeller.<br />Also, I guess its the first turn the water does after leaving the impeller and any debris tends to stick at this point. <br />I've cleaned it all out and wiped some Duralac (corrosion inhibiter) around the grommet and the dog leg channel. I'll have to wait and see how long I get out of it this time I guess.