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Old 12-17-2018, 11:16 AM   #1
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Default 2002 Mercruiser 4.2L 220 AC Exhaust Riser

Hi All. New to Maxumís, just bought a 2002 3000SCR with Twin Mercruiser 4.2L 220 AC Diesels. Iím not a novice when it comes to engineering having been a mechanical engineer for 30 odd years, but I have very little marine engine experience which is frustrating me. So, Iím after some advice.

I noticed a small trickle of water in the engine bay coming from the Starboard engine down by the transom. It turned out there is a hose, about 1 1/2" diameter that connects onto a hose tail which is part of what I now understand to be the exhaust riser. This riser is cow horn in shape and comes from the Turbo. Upon investigation the hose tail is badly corroded and the hose was not sealing. After wriggling into the near impossible space for my large frame I managed to clean up both the hose tail on the riser and the hose. I then put the hose back on and tightened the clip, all now seems to be water tight but who knows for how long. I have no history of these being changed.

Questions:

1. I assume the boat needs to be out of the water to change the riser as water is probably sitting half way up the riser / bellow?

2. I guess the riser/s should be changed. Iíve read various comments from every 5 to 10 years. She sits in sea water on the south coast of the UK. Whatís your opinions here.

3. The hose going to the hose tail on the riser, it looks like this is part of the closed cooling water, I did notice that the closed system expansion tank was out of water twice before I found the hose leaking. Iíve now topped this tank back up and am hoping it holds water. Where the hose fits onto the tail, does this go through into a jacket or waterway inside the riser, Iím assuming it does but I canít find any diagrams on the web

4. Are there after market versions of these risers available as the Mercruiser ones seem expensive at around $700 so about £500 each

5. Is there any other advise you can offer?

Thanks for reading. Darren
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Old 12-17-2018, 12:45 PM   #2
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Welcome Aboard!

Not familiar with this engine as most Maxum's have gas engines. That hose is part of the raw water system that is used to cooler the heat exchanger and exhaust. In the riser, really an elbow the water first enters a jacket that is over the exhaust wall once it makes the downward bend the water is injected into the exhaust steam to cool down the exhaust gases. Yes in salt water 5 - 10 years is life for these components. Not sure if an aftermarket part exists but for gas engines the answer is yes. Aftermarket would only exist if demand exists.
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Old 12-17-2018, 01:01 PM   #3
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Thanks for the quick reply Mike and the welcome aboard. I guess these Diesel engines are fitted to other boats makes besides the 10 or so % of Maxums. Im sure that hose ran round to the front of the engine and connected into the closed system. Ill have to check again. How about changing out the riser / elbow, would it have to be done with the boat out the water? Thanks
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Old 12-17-2018, 03:58 PM   #4
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The water line should be belies this point and about the top of the exhaust tube that connects to the inner transom plate
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Old 12-18-2018, 03:40 PM   #5
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It is common in Europe for folks to buy US boats, ship them over and then repower them with diesel. These boats had diesel options that were rarely ordered by the US market from the factory.
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