Cooling System Extremely Gunked Up - Cleaning / Flushing Advice Needed

[bnjtown]

Hey Everyone,

Recently acquired what appeared to be a great deal on a boat with a 25hp Johnson, changed the impeller and took it for a spin. After about 100 yards it started feeling hot then sputtered down to a rough idle. Pulled it out of the water knowing something was very wrong. Ran a compression test and it read the same as when I bought it (120 on each cylinder). Decided to check the thermostat and was surprised how much sand and gunk was packed under the water jacket.

Judging from the pics below how would you approach cleaning it out? I plan on pulling the lower unit off and giving it a serious flushing from the thermostat down, then from the water tube up, followed by a thorough flushing of cleaner (simple green??). Does this sound like a good approach? Certainly don't want to hurt any thing. My worry is how to know when its fully clean and free of any grit.

P.S. - It appears to me that this is a failure to maintain the intake screens on the foot - don't let this happen to you... Keep those things in tip top shape and replace if broken!

Thanks!

 

[TrueNorthist]

I literally just dealt with the same thing on my 70hp after lending it to a "friend". Your plan looks as good as mine was, minus the simple-green, and mine worked fine, so... I would also inspect the legs on the impeller for damage but they will tolerate a fair bit of abuse. If just 100 yards then you probably caught it in time. BTW, no screen will keep all sand out. Best to avoid the sand instead.

 

[bnjtown]

What order did you follow flushing it? Spraying from the top down first or from the intake tube up?

Also did you pull the exhaust plate out to inspect it? If so was it plugged too?

Thanks!