Re: 1990 omc exhaust manifold
but what do they do and why are they junk what do they do to cause problems and how do they do it?
Engines in boats with enclosed engine compartments MUST have water jacketed exhaust systems or they will get so hot they'll set the boat on fire.
The manifolds are usually cast iron and are made for a LOT of different engines and applications.
Since most marine cooling systems (in pleasure boats) use raw (lake/sea) water for cooling they start corroding almost immediately during use......slower in fresh water than salt.......but they all will eventually corrode completely thru.
Problem is, you don't really know when that happens. You have to take them apart to inspect.
Hopefully
they clog (with rust) before they rust thru.
Clogging will usually cause overheating because the cooling water cannot exit efficiently and will reduce over all engine cooling.
Manifolds with removable risers can be inspected easily......the obsolete "bat-wing" type you have cannot easily be inspected (or at all) and when they fail, they start allowing water to get into the exhaust ports and into open exhaust valves. (They don't always clog completely before they fail)
If they start leaking and your engine has been shut down for the night, week, month, or the season is over, well you get the picture.
The longer the engine sits with water on 1 or more pistons the more severe the damage.
SO, they must be inspected and/or replaced on a fairly regular basis. If your boat has been run in fresh water all its life the manifolds/risers can last a "good long time". (mine lasted about 18 years or so...)
If run in salt, they can be rusty junk in 5 years or so...and in salt, you don't EVEN want to try to run them too long.....the consequences are a destroyed engine. I have heard of some people removing their risers every year as a regular inspection.....I would think you could get away with running them 2 or 3 years without inspecting.....Bondo?
Anyway, you can't easily inspect the "bat-wings" (or at all) and if you suspect they might be getting "thin" you shouldn't put them on a new engine. It sucks, I know. and the replacements aren't cheap.
There's not much cheap about boats I guess......
