Hot exhaust hose

I found this helpful thread through Google in trying to diagnose a 'hot exhaust hose' in my boat, it's an '89 supra but has a '99 PCM GT-40 from a nautique. Anyway, I was finding my starboard side exhaust hose getting way hotter than the port side at idle (300+ versus 140) but I couldn't find any evidence of obstruction in the system. Water was getting to the manifold fine, and the manifold and riser were clear of debris, and the muffler had no obvious lack of flow issue based on a reverse water flow test.

So I took the 3.5" hoses off that connect the riser to the muffler and they looked fine inside, but I switched them and the problem switched sides. The hose has been overheated before when I didn't get the system to prime correctly, and there wasn't sufficient water getting to the manifolds. In fact, one hose had a pinhole leak in it, that would go away when the hose got warm. So I think that the hose was heating up enough to close off the little grooved water passages in the riser where the 3.5" hose goes on. At high RPM it would be ok but at prolonged idle is where the hose would approach 300+ degrees. I'm replacing both hose sections that connect the risers to the muffler and will report here if that DOESN'T solve the problem.

Just thought I'd post here to let people know who might be chasing the same type of problem, with no apparent cause.

Cheers! I hope you all get out on the water this weekend, it looks beautiful here in New Hampshire...

FWIW, my driver side Riser and exhaust hose gets quite a bit hotter than the passenger side. I plan to pull the riser to see how many shredded impeller parts I can find down there. I pulled the thermostat and found a bunch of nuggets that had been causing high engine temps at low idle.

I forgot to mention; yes, I checked the gaskets and they were both on correctly. SKIDIM also suggested opening up the blocked passage by cutting a hole in the gasket. They said it might work but I figure it should just be done right the first time. I just have a hard time believing it could be those aftermarket risers.

We checked the water flow on the exhaust side of the riser and it looks good. Called SKIDIM and they think it is the aftermarket riser the PO installed. They have seen this on some PCM engines and recommend the OEM type. This would make a little more sense why the PO had inserted stainless liners inside both wet exhaust hose.   

I haven't touched anything on the carburator but i can tell from the smell it is actually running a little rich and runs just a little rough at idle. I plan to have it kitted. The timing apears to be good but I'll check it out. Very strange.

Great idea. I figure I should do that before tearing things apart again.

Thanks for your input Pete. I definitely would have noticed when I ran it before however. I can't keep my hand on it for more than a few seconds and can tell at this temp it won't be long until the wet hose is shot. I've had some rust issues with this boat so I might remove the manifolds and or risers to check for blockage. It's the only thing I can think of. On another note; although I was pretty careful to put the riser gaskets back on correctly, if I didn't (if I put them on backwards) could this be an effect?

    search it in google, may be sutiable for you