I am rebuilding a pair of 7.4 Merc's. I am basically throwing a 300 lb person off the aft of my boat by swapping some of the cast iron parts out for aluminum. Namely the exhaust manifolds (60 lbs each x4) and intake manifolds (guessing at least 20 lbs each X2) water pumps, and a few other small things... That being said, does anyone make an aluminum thermostat housing? I really don't want to bolt this heavy ass cast thing onto my nice new air gap intake. I have found a couple SS ones out there - look nice but expensive and still heavy...

Thanks!

Since you are throwing everything overboard, get rid of the water pump also and go to a nice stainless cross over setup. Looks nice and it might save you 2 lbs.

Agreed, here you go.
http://www.rexmar.com/page161.html

I was headed down that road already! However, the one thing I still do not understand is from what I am reading, it gets rid of the belt driven waterpump... but uses some sea pump or something - that is belt driven??? Not getting it... Wouldn't you use some inline electric pump or something? I am going crossover, is there any images of a mark iv with the setup on it anywhere? I would like to see what it is gonna look like

We sell a nice Stainless Steel replacement Housing.

You already have a belt driven sea pump. You just get rid of the circ pump and use the sea pump 100%.

I don't have a sea pump, that was part of my confusion. I am running Alpha's. The new engines I am putting in are gonna be 450+ HP so may have to go with bravo's anyway... damn this is getting expensive...

Welcome to working on your own boat. I have a stainless crossover you can have if you switch to bravos. Its dimpled to fit around a procharger mounting bolt but you can't see it from above.