As for the midsection... this is a tough one.  OK, so aluminum is very porous and exhaust is very hot causing the pores to get larger.  Then you spring a water leak into the exhaust due to warped midsection components.  The metal cools and traps salt in the pores, there is no barrier coating in the block to prevent this and flushing does not help at all.  The only fix is awareness. Have it checked at your annual service.

So now you ask why did my midsection warp???

The answer is, lack of cooling coupled with MLS (MULTI LAYERED STEEL) gaskets.  There is no room for error with MLS gaskets.  Under normal conditions, with a good water pump, this is not so much of an issue.  But, when you run your jackplate all the way up and trim your engine out till the water psi guage starts to bounce so you can skip over a wintertime sand bar, you are killing your midsection from all the heat and no water.  1 of 3 things will happen

#1- You will develop an oil leak no one can find

#2- You will end up like the picture to the above left which leads to big $$$ or

#3- You will get water in your oil, again big $$$.

​C&R Marine 

C and R Marine

Certified Yamaha Technician

Yamaha Outboard Motor Repair 

Outboard Cylinder Head Repair

Most of these slideshow pictures are of rotten cylinder heads. The heads seem to be the worst as far as corrosion.  Part of the reason for it, is when casting very intricate aluminum parts the metal composition has to be more " flow able ".   Higher percentages of less  corrosion resistant alloys are used in the heads than the blocks.  You can tell what is dirty metal, and what is normal salt water corrosion.  The big pot holes with perfect metal all around them are the dirty spots and the mild  cratered surfaces usually fan out across the surface this is normal corrosion.  Both kinds are repairable if you can access them.   I  won't use heads with holes in the exhaust like shown because you just can't fix them good enough.  So now, people have labeled it dirty metal.  I guess it is to a certain degree, but its not the entire block, and the blocks that are really bad never make it to the rebuild shops.  They rotted right out years ago, so the highly concentrated spots show up fast.  More than likely if you are rebuilding an old block, you won't have any surprises.  Blast, inspect, repair any thing that could be an issue in the future, replace the exhaust kit, then educate your customer on flushing  and zincs.  I have some original 2002 F225's here that just failed and it was the head gasket surface.  I would say 15 years is acceptable, but the owner took very good care of it, and flushed it with it running.



Most people read this and think they don't have to run the engine.


This flusher

This picture is an example of

a rotten thermostat housing

The quick flush is great if you are renting a house on the water without a lift for a week or so but to flush  with this method all the time is not  the best way.

This says run it for a few minutes,

but it takes 10 min. just to warm up

so u really just started flushing at 10 min. so I recommend 15 min minimum while running with the  OEM flusher.

So in a nut shell: 

  1. Run your engine with the oem flusher when you flush it. 
  2. Have the exhaust looked at annually.
  3. Check your oil after you boat for the day.  If you do get water in your oil, you want to catch it  asap, not  the next time you want to go boating and your engine is locked up.      

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As for you guys with low water pickups(me included) duct tape it or put it in a barrel after quick flushing for 10 min. then run it for another 15 min.