What is the housing made out of?

either cast aluminum or cast iron

Stock ones are chinesium on these motors, sheet metal on some others. Real replacement ones are usually cast iron. Chrome ones are "zamac" (zinc alloy).

most of the stock ones on thirdgens are cast alum.

they warp over time though....

the better replacements are the cast iron ones.. they almost never warp... if you have enough heat to warp em, you have alot of other engine troubles to take care of first, lol

Actually, they warp very easily, from overtightening the bolts.

I always throw them away at the first hint of a leak, and get a real one (cast iron). I don't care too much for the chrome ones, because even though they are zinc and therefore make an excellent protective sacrificial anode (a good thing to have if you have both aluminum and stainlees-steel things on your motor), they always develop leaks fairly quickly and require frequent replacement.

i have this neat lil zinc weight thingy hooked under the radaitor cap of my car..... its actually ment for marine use, but idea is the same.... works great..

y?

Boat people will know exactly what this is all about.

Basically 2 dissimilar metals immersed in a conductive solution with a conductive path between them will create a battery. One of the metals will act as the cathode and will accumulate metallic ions out of the solution; the other will act as an anode and will have its metal atoms stripped of electrons, turned into ions, and dissolved, thereby eroding the metal. In the case of the stainless/aluminum reaction, the aluminum acts as the anode, and ends up getting eaten up and pitted and ruined. The process is continuous and inevitable.

In the case of a car motor, the antifreeze is the solution; and the other parts are the aluminum castings and radiator, and stainless fasteners.

Putting a large enough zinc object nearby, immersed in the solution and electrically connected to the stainless and aluminum parts, will cause the zinc to act as the anode (and erode), and allow the aluminum and stainless to both acts as cathodes, thereby preventing them from eroding. That's why various parts of a boat outboard motor or outdrive are made of zinc, and why there's zinc lump things you put on stainless propeller shafts of inboard systems.

RB83L69 gave the full complete explanation, but in laymans terms

it keeps the alum radiator and heads from corroding away. the zinc goes instead....

my lil zinc weight thingy is lil bigger then 2/3s the size it was when i put it new... $2 on a piece of zinc is nothign compared to new manifold or radiator... that and i got it for free when my dad had one from a boat he sold..

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protective sacrificial anode (a good thing to have if you have both aluminum and stainlees-steel things on your motor)
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ah ha totally missed that part in ur first post good explination.. and intrestin idea MrDude never heard of ne one doing that before