exhaust hose smoking

[denwbaseball]

1987 Supra w/V8 351

The problem is the final exhaust hose after the riser is smoking...Here is where I am at.

There was smoke coming from the exhaust manifold at first so I ordered a new gasket for the manifold and a brand new manifold just in case I needed it. The manifold gasket was junk along with a few bolts that had to be cut out. So I changed the gasket(also change the valve cover gasket). Now the the big hose is smoking and not the manifold.

And it doesn't start smoking right off the bat it starts after running for several min. I look at the back two baffles and an even flow of water is coming out of both. I unhooked the hose from the riser and there is no blockage.

Should I just get a new hose? Or is there something else I should be looking at?

[92SupraComp]

something sounds really wrong. do you have to large muffler that sits right behind the engine like ours??

[crystal waters]

not sure if this helps or not but what color is the smoke? Black? Whitish? etc

[denwbaseball]

There is no large muffler. And the boat runs great and doesn't run hot at all....
The "smoke" is white and its not a ton of smoke if I keept the engine cover closed I'd probably never notice it.

[denwbaseball]

It's almost like there is oil or something on the hose and when it heats up it starts to smoke. But that doesn't seem to be the case.

[SquamInboards]

What temperature is the hose? Can you put your hand on it? It should be under 150, or at the very most still under 200. Mine run around 130-140 at idle. I had a weird issue this spring where the exhaust hoses were getting very hot, like 300+ and they still didn't emit any vapor. It sounds like a tiny leak somewhere that's creating steam, in your case.

[denwbaseball]

I could put my hand on it for a second or two before I'd have to take it off running it above idle.

So just a new hose? Maybe I damaged something taking it off and putting it back on when I was messing with the manifold?

[SquamInboards]

You might have damaged the hoses, possibly right under the hose clamps? If they've been on and off a few times the clamps could have damaged the hose enough to allow a tiny leak. It could be more noticeable at first startup, before the water starts to evaporate. If it's after the manifold it wouldn't prevent the engine from cooling properly or even cause any problem with water flow, but it certainly would be enough to create some steam.

Of course, it could be something else entirely, but it's free to check for leaks. Maybe try starting the boat and running for 90 seconds or so, then looking for a drip or wet spot, before it gets warm. If you can't see it then, run it up to temp and look carefully to try and find the source. That would at least narrow it down. New hoses aren't cheap or especially fun to install but it sounds likely you'll be doing it soon. You can get the right hose by the foot from skidim.

[denwbaseball]

Ok so today was a nice day without wind so I could tell exactly where it was coming from. The smoke is coming from hose just after the riser about were the clamp is for the riser. And most of the hose isn't hot at all but right where the riser is its real real hot. Move down the hose 6 inches and you can keep your had right on the hose no problems.

[92SupraComp]

well that should be the hottest point as that is were the water and exhaust come together. you should look up a cut away version of these manifolds.

[denwbaseball]

I want to take the riser off to inspect. Any advise on getting the back to hex head bolts off?

[denwbaseball]

Ok so the riser is off. Now what am I looking for to tell if I need to replace it. I will say that the very "end" of it where the water and exhaust meet its very black just like the inner exhaust chamber. Should there be this much carbon build up? Also I noticed that on the hull where the water blows out there is a carbon build up on that as well but just the one side.
Is it time for a new riser and all my "hot" problems will be solved?

[CornRickey]

I'm wondering if you have a blockage in the water jacket on that side. Is run the motor and hit all of the exhaust ports with a infered thermometer to compare temps .

[SquamInboards]

You separated the riser from the manifold before, right? There is a blocked port in the gasket that should be toward the stern. This forces water to go through the port that goes up and over the top of the riser, and through the sides, rather than taking the shortest path. Was the gasket installed that way?

[kreckley]

If your impeller is not drawing in enough water or your water pump is blocked or one of the lines or water jacket on your motor from an old impeller shredding IT will run the exhaust hot and usually the right one will burn through first Fire Hazard!!! You have a problem with cooling be careful This can be a bitch to find and clear