Re: Replace those Risers and manifolds!
What fails in the manifolds? Aside from abusive failures (heat stress, ice damgage) your biggest enemy is the salt corrosion. It eats away at the iron something fierce. It also causes deposits and scale on the walls, which flake off and clog the system. Even when the deposits don't flake off, they are narrowing your water chanel and insulating your cooling water away from the heat it is supposed to be sucking up.<br /><br />When these problems don't kill your manifold you will often find the machined surfaces at the riser eroding away - leaving you with less and less sealing surface between riser and manifold. <br /><br />Plenty of companies have tried coating or galvanizing the interiors of the manifolds. Merc, having the biggest budget, has been the most successful. <br /><br />One of the hardest challenges to overcome with coatings is the physical problem of coating a very complex, very narrow, set of channels. Add to this that you are working with a product that constantly grows and shrinks with heating and cooling, that has one face very hot, while the other face is very cool. Again add to the equation the penalty for failure: bad manifolds are expensive. <br /><br />Problems with coatings include coatings that fall off usually in large flakes (many ceramic coatings have this problem), and coatings that are not complete thus leaving a small section of wall which is attacked quite vigorously while being out of site and out of mind.<br /><br />Perhaps the real problem with coatings, which is tied up with all others, is cost. It is expensive to do, and may fail anyway. Most smaller manufacturers will be scared of the outlay to create a product they are not sure of, while opening themselves to the possibility of massive failures. <br /><br />At the same time, while all boaters will acknowledge wanting a manifold that lasts longer, actually paying for one is another story. I recall a gentleman who made solid brass manifolds for Volvo 4-cyl. He gave it a lifetime warranty. He was out of business quite quickly, as nobody wanted to pay the price for it. While the added cost of a coated manifold is not very noticeable when you are buying a new engine in a new boat, it becomes very much a sore point when a customer calls and asks the price to put a new manifold on his 6 year old boat, and even worse when you are are trying to repair an old beater boat on a budget.
