M-25 Coolant Change

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Cedric Thevenaz

I have a 1983 Catalina 30 with an M-25 engine. Can anyone tell me what is the best way to flush out and replace the fresh water cooling fluid. I have a water heater and the fresh water lines go all over the place. Any of your experiences would be helpful. Thanks kindly.
 
Feb 26, 2004
23,075
Catalina 34 224 Maple Bay, BC, Canada
M25 Coolant

Cedric Easiest way is to take one of the hoses to the HX off and carefully drain it into a bucket. There is also a manifold drain under the edge of the manifold. Stu
 
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Brandon

Nothing to be afraid of!

It's a bit late, but I enjoy replying to the forum, so a few more minutes won't hurt. I just did major surgery on my 84 C30's cooling system. Pulled the heat exchanger due to wealth of corosion. The little zinc on the bottom, port side crumbled in my hand. Be careful if you intend to replace it and be prepared to find a radiator "artist" who likes a challenge(if the zinc mount detaches). Anyway, the lowest point to drain is at the mixing/diverter valve setup(stbd/aft) in the engine box. Unhook one of them and prepare to catch the fluid. I had to drain it a few times and found the best and most environmentally freindly way is to have a wet/dry vac to suck out all the fluid as well as clean up any that gets away into the bilge (vac your bilge dry before you start). It is very thorough about drawing all the fluids out of the engine, manifold, cooler and h2o heater. Once you refill, run the engine and keep an eye on the coolant level in the manifold. As the engine warms, open the small valve at the thermostat housing to let the trapped air escape. Put the cap on and go to the small valve at the inlet hose to the h2o heater and open it enough to allow any air to excape. Once the engine is up to temp, cap on, etc. don't forget to fill the expansion tank about half full. Find great diagrams at http://www.tcsn.net/bosun/c30/techdrawings.htm
 
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