I thought aluminum was bad for marine motors???

[Kikwear]

Seems everywhere I look, I see aluminum for boats. Intake and exhaust manifolds, heads, risers, etc. I was told that since the block is cast iron, the expansion and contraction rates can cause problems with gaskets and such. If that was the case, how come nobody makes cast pieces? Is it all about weight? Even with an open cooling system, corrosion could be a problem. Am I looking in the wrong places or and I being fed misinformation?

[Cuda]

Aluminum is bad for salt water boats. Cast iron+aluminum+saltwater=a battery. Electrolisis will eat up the aluminum.

[MOP]

Aluminum is not the evil demon some would think, even in salt I have seen intakes do well with flushing and exhaust last for very long time, zincs will help to extend the life span. No doubt closed cooling is the hot ticket, both for protection and performance. The deterioration of aluminum is not restricted to just salt water, many people have reported noticing small pock marks on drives even in lakes an rivers. I found a few after the 1000 Island run which was the only time my boat was left in the water. The expansion and contraction issue I feel has been greatly reduced if not eliminated by much better quality gaskets, there are millions of cast iron blocks with aluminum heads true mostly in the automotive field which run hotter temps than most marine applications. Some marine aluminum manufacturers I have contacted claim the coatings they apply today will outlast iron. A few preventive measures and good flushing will keep stuff in good shape a lot longer than most would think. All exhaust parts connected to the outdrive and the outdrive its self is aluminum many of which are many years old.

[Cuda]

Here is a picture of an aluminum intake that failed in salt water. This is after it was repaired.

[Cuda]

Here is the result of that failure.

[Forrest]

. . . and you could go on to say that outboard motors are made almost completely of aluminum too, but, I think that you will find that the grade of aluminum used to build outboard-motor power heads is much different that the grade of aluminum that is used in the manufacturing of automotive intake manifolds, heads and blocks.

Always remember that when two dissimilar metals are immersed in and electrolyte (sea water or mineral laden fresh water) galvanic corrosion will occur. Also, corrosive action increases as the temperature increases. The result is shown in the photos in Cuda's post above.

[BillG]

Just a thought.
I have been running my 18 in salt water, and it stays in all summer, for 32 years. The drive is none the worst for it, because of good zincs. I have used aluminum and cast iron exhaust manifolds. I have had less trouble with the aluminum than the iron. I am replacing the iron this year and going back to aluminum. I flush after each run with good results. My aluminum manifolds have lasted at least twice as long as ths iron ones. They seem to corrode out from the exhaust side instead of through the water jacket into the exhaust. They do not flake off in big chunks internally like the iron ones.
Just my .02 cents.

Bill G

[MOP]

Zinc and Zinc and touch up chips on exterior stuff aluminum will be around for a long time. How many guys remember the AQ 100 drive? I know where one is that has been in salt its whole life must be atleast 35 years old. BillG has brought up another very good point, cast iron manifold will flake off fairly big pieces at times cousing overheats even if they are relitively new. Anyone how is or has been on the wrenches has cleaned risers and reinstalled them because they still had pleant of meat. Alunimum does not do that and they do seem to last longer. Intake manifolds were mentioned before and true it is mostly the material used. I was just given a Merc Y pipe to use with the BH drive, it came off a boat that was kept in the water for years and is still in great shape. Also when disimilar metals are bonded to each other correctly and zinced they do very well and will last like if not better than cast iron products. Hmmmm! lets try cast iron out drives they would be Hell for Strong!

[Kikwear]

I'm confused by flushing. Do you mean when you get home, put the cups on the drive and flush it out? What kind of zincs, precautions and flushing would be needed to run aluminum intake, heads and exhaust safely in Lake Michigan water?

[MOP]

I used to make up a home made kit for my clients, I would take a brass T with what ever intake hose size was on for the straight through, on the other I would go to 2 inch with a brass reducer to fit a 3/4X2" zinc. I went to 2 inch on the T to insure there was good flow around the zinc. On the shoulder of the reducer I drilled and tapped a hole for a ground wire to be attached, Which then ran to block ground put 2 pipe nipples in it and cut the intake and slipped it in and clamped it. It ends up weighing about 2 pounds so I would also clamp it down to the block or stringer. Most any marine mech will tell you 3 maybe 4 seasons on risers, my guys were getting at least another season or two. All of what happens inside cast iron is not corrosion, it is also electrolysis a well grounded zinc will help save stuff. I always emphasize well grounded meaning bonded well into the system, drive and trim tab zincs attaching points should be clean and bright and the zinc must be installed tight. If you have doubts about the contact surface use S/S star washers to get a good bite. I check my zincs with a ohm meter every so often just to make sure. Like many I have seen some pretty bad destruction caused by improper zincing.

***Note the zinc in the T in some cases needs to have a tad cut off the end so it does not bottom out***