Exhaust Risers

[Sdc77]

Hi guys,
Wonder how hot are your risers after a cession ?
Mine are hot. I still can touch it with the hand, but can't stay a long time. I don't have a thermal tool to check, but i will say about 140-150°F. After a Wake cession, not going over 2500rpm, in a 60°F river water.
Is that normal or too hot ?

[gnarlydude]

What's your temp gauge say?


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[Sdc77]

170°F off idle, 190°F idleing
Seems then logical for the riser temp ...

[Jetlink]

Funny that you mention this...long story short my boat is in the water in the lift for the summer but I'm hesitant to take it out at the moment because I overheated the port exhaust hose on the way over to the lift from the launch and have been troubleshooting since then. I've even managed to stump Vince at skidim. Anyway, I have an infrared thermometer that I've been using and the very top of my port riser is sitting around 160 degrees American when I've had it out to test it while the starboard riser in an identical spot is around 110.

[CJD]

160 degree F (or American, LOL) water at the thermostat is mixed with 1200 degree F exhaust gases in the riser. The riser will have to be hotter than the thermostat. If you can put your hand on it, it is fine.

[Sdc77]

Thanks for advises guys :)
It runs pretty good anyway and the engine is never overeating

[SquamInboards]

Funny that you mention this...long story short my boat is in the water in the lift for the summer but I'm hesitant to take it out at the moment because I overheated the port exhaust hose on the way over to the lift from the launch and have been troubleshooting since then. I've even managed to stump Vince at skidim. Anyway, I have an infrared thermometer that I've been using and the very top of my port riser is sitting around 160 degrees American when I've had it out to test it while the starboard riser in an identical spot is around 110.

So... is one of your exhaust hoses getting warmer than the other? Is this all the time? Or just at idle?

The reason I'm asking is you may have seen a thread from me about my exhaust hose overheating... here's the link. https://forum.supraboats.com/showthread.php?16251-Exhaust-hose-overheat

TL/DR: I replaced my hoses with VHT Silicone hoses that are rated for 450F* (*I think).


To the OP on the riser temp, as others have said: the ballpark of 160F is "normal" but a good test without a thermometer is if you can put your hand on it but not for long, then that's ok. Like, more than an instant, but not 10 seconds maybe.

[Jetlink]

Here are my latest numbers after a quick run around the bay to see if I cleared any obstructions in the port manifold and riser.

Lake temp 74.0

Port water inlet 123.5
Port riser 180.5
Port manifold 127.0
Port exhaust hose at riser 115.5


Starboard water inlet 103.0
Starboard riser 119.5
Starboard manifold 126.0
Starboard exhaust hose at riser 109.0

Drip less shaft seal 128.5
Thermostat housing 140.0

[NoWake]

Here are my latest numbers after a quick run around the bay to see if I cleared any obstructions in the port manifold and riser.

Lake temp 74.0

Port water inlet 123.5
Port riser 180.5
Port manifold 127.0
Port exhaust hose at riser 115.5


Starboard water inlet 103.0
Starboard riser 119.5
Starboard manifold 126.0
Starboard exhaust hose at riser 109.0

Drip less shaft seal 128.5
Thermostat housing 140.0

Your welcome to shoot mine at the reunion or I can bring my thermal gun. Sorry to say but I still need to water test my comp before the reunion as it has been crazy here. Did you burn a hose or just got suspicious? I know you have the PSS dripless, would be interesting to test my OJ at the same spot and compare after an identical run.

[Jetlink]

It totally blew a hole through essentially what was brand new exhaust hose right where the riser went into the hose. I've taken the entire system apart to check for obstructions and water flow and I cannot figure it out. Taken the riser off the exhaust manifold and cleaned it, checked the passages for obstructions and those are clean. Installed new gasket between the riser and manifold as well. Went in the front and back of the manifold and checked the passages for obstructions and can't really find any. I get water out the back and not just a little bit but it is less quantity and less velocity than the starboard side and also less than when I ran it on the trailer before I dropped it in.

[NoWake]

I'm assuming you replaced the burnt hose and or looked at it for it's internal integrity? "stumped" Vince... What are we missing?

[Jetlink]

Yeah, replaced both hoses and have stumped everyone that I have spoken with about this issue.

[SquamInboards]

Yeah, replaced both hoses and have stumped everyone that I have spoken with about this issue.

I read back through my thread about my similar issue and was reminded that some suggested a blockage in the exhaust system somewhere AFTER those hoses. Maybe a nest of some kind over the winter... there could be some debris in there blocking the flow somewhat.

I somewhat eliminated that possibility with a non-scientific flow test - both directions - I had the hoses off with the boat in the water and let water freely flow into the boat from each side, one at a time, by tilting the boat. No visible difference and PLENTY of water came in. Same on land, I've had the hoses off and looked at idle water flow out the dual exhausts. No visible difference.

So is this happening to you all the time, at all speeds? Or is it worse at idle? Mine are fine at higher speeds, but get hotter at idle.

I know you probably don't want to go this route, but the high-temp silicone hose I used on my exhaust has "solved" my problem by allowing the temps to creep up on the hoses without damage. The temps never get high enough to cause damage to anything else, but I'm on my 3rd season with these and I haven't looked back.

Like you, I went through everything possible and stumped everyone I talked to. I worked at a marina at the time I had the issue and no one there could figure it out either. I remember thinking "what would we do if this was a customer's boat?" and not having a good answer (aside from the "solution" I did implement) unless they wanted to start throwing parts at it. New manifolds? Maybe, but no way to know. That's a lot of money. New mufflers? Mine are under the floor. $$$$$. What else is there that hasn't been looked at?

The only thing I haven't changed or otherwise eliminated is the RWP itself. In fact, I think you suggested perhaps a slightly larger pulley to increase flow... not a bad idea but I haven't gone down that road. Clearance to the doghouse is an issue, for one.

I'm happy to think/talk this through with you some more because although your higher-temp hose is on the opposite side to mine, it sounds extremely familiar.