Replacing Exhaust Manifolds?
 

Most of us know that if a water jacket rusts out inside an exhaust manifold, it can have disastrous consequences.

Should they be replaced after a certain number of years or hours, before they cause extensive damage? How does one know when they should be replaced?

Should they be replaced with OEM manifolds, or are aftermarket ones [perhaps aluminum ones?] just as good or better?

Thanks for your thoughts.

Great question! I'm not sure myself, and would be interested in knowing.

If memory serves, I think there's a severe corrosion issue if you mix aluminum with the cast iron (but I don't know if that's only in saltwater and/or something with the "Mercathode" system). I also seem to remember issues with temperature fluctuations and expansion, but I'm not sure. I'm definitely no mechanic, but I'd be interested to see what the experts have to say on this.

To check your manifolds just pull your exhaust hoses off each side and hit the manifold with a mallet. And look for debris. IE rust chips, flakes etc. Im not a huge boat guy but It seems to me the liner dropin rucst chips will tell it all.

I would double check this but if my memory is correct. It is inspection every 2 or 3 years and replacement at 10 years. This is for fresh water. Inspection would be removing the riser from the manifold and visually looking for corrosion. Single piece manifold cannot be inspected and should be replaced(see my ordeal in "4.3lx owners listen up!)

HTH
~J

I decided I would call the service department at Mercury Marine, [here in Canada]and ask these same questions.

Unfortunately, they did not have a definitive answer as there are quite a number of variables I was told. The age of the manifolds, proper winterization techniques, hours of use, and the type of water the boat is used in, [fresh, brackish or salt] all play a factor.

So, having said all that, I'm still trying to decide what to do...

Mine are 15 years old, but don’t know the exact number of hours. [no meter in the boat] I'm guessing maybe 350, by the condition of the rest of the boat. I know it’s been used only in fresh water... so....

Decisions... decisions... :D

It wouldn't hurt to get tose manifolds replaced after 15 yearsl

HTH
~j

Manifold replacement
 

I own a 1998 180 Shabah which I use in salt water. My mechanic doing a routine check showed me the inside of the manifolds. The looked everything else but a real manifold. They were replaced by aluminum ones and they work great in addition to take several hundred pounds from the boat. Go for it!