He is my problem. I purchased two use salt water Merc 440HPs. One needed head work, when the head was off the builder noticed the cooling channels had very heavy deposits from lack of flushing and most likley storage with salt water in them. He cleaned all the channels or that one and the motor runs great. Now the other engine (un touched) runs at least 40 degrees warmer and gets very warm at long idle.

I don't want to tear down the heads this late in the season, especially seeing that these were purchased for spare engines. Is there chemical out there I can use to break this stuff down? I have good flow through the oil cooler, it is new. If I could find something to just leave in the block with the pumps and cooler by passed, then back flush I would be a happy guy.

FYI, new sea pumps and cooling system on both, I am sure it is the internal corrosion causing this problem.

Ttt ??

Run some salt-a-way through it.

I wonder just what the mechanic did to relieve the debris?
If it's heavy rust particals lying in the bottom of the block, it will cause a cooling problem due to the reduced water contact area. Rust build up in the heads is real problem, too many small passages to clog.

Only way I know to clear it out is pull the engine, tear it down, and have the block boiled. Same for the heads.

If you can get at the casting plugs in the block could you knock them out and runs some wire in there and flush? Any idea what Muratic Acid would do? Might just make it worse or could eat all the rust out. Not recommending it, just a thought.

When the rebuild was done he did hot tank it, but he told me the build up was only in the end ports where the heads, block, and intake all meet. I did not know there was blockage until this motor was heating up and I asked him about it. I wish he told me when they were both on stands/

I pulled the crossover off the front and housing off the top last night, could not believe the crap in there. Knocked it out and shop vac'd it up.

I took a chunk of the stuff and dropped some acid on it, eats it right up. I too am scared to run acid throught the engine.

Anyone know if acid will harm the cast iron block, heads? How about the head gasket and brass lining for the intake?