I was out on the lake today and For some reason I stopped and opened my hatch and I saw a little bit of water on my exhaust manifold by the riser, so I wiped it off and just thought that some water splashed in through a vent.
When I stopped again and opened the hatch there was more warter there so I wiped it off and watched it and sure enough it was leaking out of the riser gasket not leaking bad just seeping out, OK its obvious that I need to change the riser gaskets but what else do I need to do to check for other damage to the engine

I will assume that you are referring to stock Mercruiser exhaust so chances are that if water is leaking out, it is leaking in as well. You should immediately pull the risers and check down the manifolds for any signs of water or rust. If it is only a little water leaking in, your motor is going to be o.k. But, you don't want that cold water dripping onto those hot valves, so do the job now. Also, when you have the risers off, put a straight edge on the gasket surfaces to check for any warpage. When you go to your Mercruiser parts store, make sure they give you the later model of riser gaskets, they should be silver in color, and have little dimples all over them. If they are black and have a red print-o-seal running around them, they are no good.

I just noticed my EMI Thunder exhaust seeping water from the riser gaskets also! I assume you'd have to use their replacement gaskets correct? Or is there a better material?

ZP'd

I have one question !!
Are these Mercruiser 454's of any design & cast iron exhaust???

If so, it may NOT be the riser that is leaking. It sure can appear to be..... My risers were corroded so we milled them. Fixed that problem......still found little drops of water on the exhaust right next to the risers.....always in bubbles not a stream.... found hairline cracks in the manifold itself. A common problem that probably will not hurt anything.....as long as the crack is not internal. I will replace mine next season with headers....until then, no problem!!

Checkmate is correct. The later style gaskets will resolve the problem providing the risers aren't too corroded or warped. If there is rust/scale on the mating surface, gently sand with a 400 grit cloth. Insert rags in the manifold to prevent the grit from going down near the valves. Be sure to retorque evenly when tightening the risers. Though not critical, it helps.

ZP'd
i put two new sets of EMI's on this year. one set leaked because the riser sealing surface wasn't even close to straight. i had to use a sander to smooth them out and those EMI gaskets are pretty crappy too. i made new riser gaskets out of cork which haven't leaked since and used merc gaskets on the head that don't need the retorquing that the EMI's do. on the flip side, they sound great and the power over stock was much improved.

hey these guys are right,address this immediatly,when its stored it may also have leaked down into your manifolds,tear it apart and inspect for warpage,corrosion,etc immediatly....thats were we make most of our money,leaky manifolds=stuck motors=race boat monies.....EMI manifolds do work well with extra torque and horespower,BUT require a little extra attention during installation,and after the first few runs,but work great....you can even use a barr thick paper gask in your stock mercury exh risers.

Thanks guys,

excaleagle42,

Sounds as though I may want to check them with a straight edge huh? Curious on the cork gasket, did you use a gasket sealer such as permatex or anything or just install the cork gasket dry?

It seemed odd to me that after only 75 hours of freshwater use they'd leak. I'm not that mechanicaly inclind to know much about the aftermarket exhaust on this ride so all the suggestions are greatly appreciated! Didn't want to screw anything up but it looked liked a pretty simple job to tackle for even me!

I'm going through this now. Boat has only 80hrs on it but it's on its 3rd set of riser gaskets, starboard side only. Got the straight edge out and sure eneough it was warped bigtime, I don't understand how it worked at all. Even the parts guy said "holy chit." Got the riser milled for $20 but I haven't put it all together yet. I was told to file the manifold if thats not straight but I'm hoping the size prevents it from warping so much. Good luck!!

ZPD
i didn't use any sealant with the cork gaskets. the surface was much more agressive after the sanding so sealant wasn't necessary.