I'm cross-posting this here, I had been following a couple threads on CCFan about this topic and I thought I'd see what you guys think. I thought I posted this here when I had the problem, but I couldn't find the thread. So here goes.

My boat does a lot of idling, often for night cruising when it's chilly, so we don't want to go fast. Now I've started taking my son for "boat naps" where he sleeps while I drive around the lake (he's almost 2 years old), but again, more idling. Last weekend it was over 3 hours straight.

The problem I had two years ago (and now again) was the exhaust hoses were getting extremely hot, like 250-300 F (they are rated for 250 F). To be clear, we're talking about the 3 1/2" ID hoses that connect the risers to the steel elbows that are in the floor of the boat.

I narrowed it down to an internally collapsing hose, which was preventing water from escaping the riser and cooling the hoses at low speed. At higher RPM the water was forced through, so cooling was no problem. It was worse on one side, and I was sure I had found the culprit because the problem followed the hose when I switched sides. So I replaced the hoses and had no problems thereafter. That is, I checked them multiple times that summer after long idling periods, and they were fine (under 200 degrees at all times). I don't think I even thought about the problem last year, since I had no symptoms.

I was out in the boat this weekend and noticed the hoses getting hot again at idle (I smelled burning rubber in the exhaust fumes), but no problem at speed. The risers are normal temps, all the time - never over 160. I think that because I do a lot of prolonged idling, the hoses get a little too hot over time, and break down around (basically melt into) the channels that allow water to pass from the risers to the hoses. Then the problem is self-perpetuating, as less and less water passes through at lower speeds, and the hoses get worse over time. The engine temp is always dead on normal, and I've cleaned out my manifolds and risers, there's no flow issue in there, I'm certain of it.

I don't think there's a back pressure issue, because the engine always runs flawlessly, and plenty of water comes out the exhaust when I run it on the trailer. The problem is the same on both sides, and my boat has full dual exhausts. The problem went away COMPLETELY with the new hoses, and has slowly returned.

Since the hoses get hot, but never more than 300, I am going to put the higher-temp silicone exhaust hose (rated for 350F) in place of the old stuff, since I now have to replace it anyway, and hopefully that will be the end of it. I hate to mask the problem with higher-tolerance materials, but I genuinely think there is no design issue, and no water flow issue, it's just that when you idle for SO LONG, it slowly weakens and collapses the inside of the hoses, until they get less and less water through the channels, and it's downhill from there.

Anyone have thoughts on this? Am I crazy?