I have the same exhaust on my OMC Cobra 4.3 V6, couple of suggestions: each bolt or fitting you put into the exhaust, coat the threads with OMC/Evinrude gasket sealer because it will keep the bolts/fittings from seizing in the cast iron. When removing fittings from the old exhaust elbows, heat the cast iron around it to get it to expand just enough to break the grip of the corrosion on the threads. When re-installing manifolds always use new gaskets, and take an exhaust manifold bolt to the hardware store. Buy 2 longer bolts, same thread pitch. Cut the heads off, and cut a slot into the stub for a screwdriver. Now you install these 2 in the block, with the side with the slot facing out, and next slide the gasket on. Then slide the manifold on. Now install the rest of the bolts. Last remove those 2 headless bolts using a screwdriver in the slot you made. Then install the last 2 bolts. This saves you having to juggle the gaskets and the heavy manifold. Same trick works on the exhaust elbow bolts. Just buy 2 longer ones, cut the heads off, cut a slot to remove them, helps keep the gasket and elbow lined up. Save the headless bolts for the next time you have to change them.

The useful service life of the manifolds can be further extended by sanding the sealing surfaces flat, giving new wider surfaces. The process is described on the left side of the manual/instruction that you showed in the video. The workshop manifold says to use 80 grit aluminum oxide paper or to mill the surface. I mounted abrasive paper onto a piece of glass and sanded manually. Where I live we have brackish water so my manifolds were not as corroded as the ones you got though.

Interesting the instructions say not to use gasket sealer on the riser. I’m putting new manifolds and risers on mine at the moment and the instructions say explicitly to use sealant and even give example products and part numbers.

Hello Sir. How did the boat run with the manifolds after cleaning them inside? Did you had any leackages? The gasket was original ones? Also do you think i need to buy the new elbows and plugs? thanks a lot for your video!

Can you do a video on winterizing process please? (That is if you live where you need to winterize)

You did not show how you got the new/old engine side gasket on. Curious how it fit on. I just bought a 2004 boat with a 3 L penta. I'm going to pull the riser and inspect it before I decide I need a new one. No indications it's a problem yet!

Can you also share the cleaning process?

Hi did you had to replace exhaust manifold Gaskets also?

My mercruiser manual says to pull them apart and clean them with muriatic acid

Where did you buy them and how much were they?

Seems like you don't flush after you ran your boat in salt water.

I am in the same boat. What is the status of the repair?

What you used to unclog that pipe that was carbonized?

My boat driver side plug holes are filling with water gasket is fine everyone saying it’s a manifold?

Are you running your boat in saltwater?

At least on 3208 elbows your not supposed to

Has that boat been used in saltwater?

Was the boat overheating before you changed everything?