[QUOTE=Thunderstruck;2126788]I bought anodized AFR aluminum heads for my 500HPs. Although I flush religiously, the heads corroded in a year to the point where water was spraying out between the deck and the heads. I boat in brackish water.

I have gen 6 blocks, the heads are based on gen 4 GM style heads. The gen 6 blocks have elliptical or triangular water passages. Gen 4 heads have round holes for water passages that are smaller than the holes on the heads. So, the head gasket sealed on the triangular part of the head gasket and held water between the head gasket and the head which did the damage.

In my case, all it took was a few trips into salty water and the damage was done. BTW, the main part of the water passages that was anodized looked great. I just had crevice corrosion on the face of the head where it meets the head gasket. Welded up the heads and installed closed loop cooling so the problem should be gone.[/QUOTE

What was your fix for the difference in the water passages on the head as opposed to the oneson the block? I ask this because this is exactly what I'm doing now, putting alum. heads on my gen6's and I'm sure that the heads have round passages.

The Dart intakes that are on our Hp 500's are 12 years old and don't leak and they have spent there whole life in salt water. It's just the heads on Gen 5/6 blocks that don't last . I am not saying that they are not corroded they are the t-stat will drop into the bottom of the water passage of the intake but they don't leak .

Welded up the heads and reinstalled with closed loop cooling. The biggest heat exchanger SeaKamp has without being specially built. $1K/side to buy and install.

The heat exchanger is about 6" diamter by 3' long, 4 passes (4 passes is critical) Holds the water temps with no tstats to 120-140F. I could not get thermostats to work.

It looks like you could have had some electrolysis going on. Cathode protection can help reduce corrosion where dissimilar metals make contact. Anodes can also be placed on the motor itself.


Darrell.

The heads don't touch the block due to the head gasket. Look at a head gasket (I used Felpro) that is designed to mate a gen 4 style head to a gen 6 block. There is a triangular shaped permatex seal with a round seal inside the triangle. The triangle seals on the triangular water passages on a gen 6 block and does not seal the round circle of permatex. Therefore salt water can seep between the head and the head gasket and stay there. No amount of flushing will help. Salt away will not help.

Just got a call from a guy with the same problem and I am sure there are other people.

I would think that a gen 4 style head installed on a gen 4 block would not have the problem as there are many people who have had aluminum heads in salt water and gotten decent life out of them.

My issue was bolting a gen 4 style head to a gen 6 block with the head gasket that has a couple different seating surfaces. I chose to install closed loop cooling to fix the issue and I have run the motors for 2 years with closed loop cooling.

Is there another head gasket that will not create crevices for salt water to creep into and stay?? Maybe someone can chip in with some head gasket technology which would be cheaper than closed loop cooling.

I bought some AFRs about 1 1/2 years ago and they rotted out already. Marine oval port 265. Head gasket blew, and when heads came off I saw lots of pitting o the deck surface. Always flushed it so I thought they would last 5-10 years. Going to go back to cast iron heads, I cant have this happen again in another year or two.

thread is 8 years old,none of those aluminum heads are as old as this thread.

If I boated in the ocean, which I don't, you bet my azz I'd be running closed cooling. Even with cast iron.

IMHO.

Hell, you can even get corrosion in fresh water, especially if you have some stray current and don't realize it. Merc definitely headed in the right direction when they started offering closed cooling on all of their new engines.