Logo
FULL SITE MENU

Cooling System Cleaning Advice

A

arkansashunter

Member
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!

Johnson thermostat.jpegJohnson Water Jacket 1.jpgJohnson water jacket 2.jpeg
 
Thanks for the reply.

The motor is a '93.

Good idea on the exhaust and head, will pull those off and inspect too just to make sure nothing got inside the motor.
 
I hope you are right on the crankcase. So do I need to pull the exhaust plate and inspect after I flush just to make sure everything is kosher there?

In regards to the thermostat spring, I have not inspected it yet beyond the picture (in the 1st photo it is laying on top of the head - as you can tell it is fully packed with sand. Was just going to order a new one to be on the safe side and not bother with testing it)

After seeing this I think it would be a good idea to pull the covers off my 15 year old 25 merc. Its my duck hunting rig and it gets rode pretty hard through all sorts of nasty mud and leaves etc. I always flush it and keep the impeller changed but never though about checking the water jacket.
 
Got her all flushed out with the water hose. Spit out some pretty nasty stuff then started spraying harder and clean. Flushed from the thermostat hole down, then from the brass tube up. Then flushed with the thermostat hole plugged up. All seems good. About to order new gasket and thermostat so I can put it back together and run some saltaway through it.

Will post results.

Anything I missed? Thanks again for the help!
 
Back
Top