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Rubber exhaust hose heating on one side, good water flow new manifold and riser 5.7L carburetor

T

technish

New member
I am trying to find out why the rubber tube is heating up on the even bank of engine. It is a 1993 Crusader 5.7L carborated inboard. Details are the even bank rubber hose past the riser is getting 200+ degrees while the odd bank stays around 90 degrees warmed up. New parts are manifold, riser, thermostat, tstat housing and Impeller. I ran it with rubber tube off riser and there is tons of water flow on top and bottom coming out of riser. Timming and plugs are good and I dont suspect a clogged exhaust anywhere. It's kinda strange. Anyone seen an issue like this before? Thanks
 
Is it raw water cooled or does it have a heat exchanger?

Does the engine have log style exhaust manifolds (older design) or center riser (newer) manifolds?

"I ran it with rubber tube off riser and there is tons of water flow on top and bottom coming out of riser." - which hose are you referring to and exactly where is the water flowing from???
 
Raw water cooled fresh water boat, center riser. I removed the 4" rubber tube from the riser on the affected side and ran the engine, I got aprox 1.5 gallons of water in 15 seconds from the outlet of the riser. There is a wide water outlet on the top exit side of riser and a 1/4" × 3/8" hole at the bottom. Plenty of water flowing from them. Ty
 
Nevermind...newer center riser style....

so you are removing the 4" exhaust tube and getting 6qts of water in 15 seconds....at what RPM?

what event caused the parts changes?
 
what does the exhaust system look like from the 4" exhaust hoses back thru the transom?
in other words what is the configuration of the exhaust?
 
I'm getting that flow of water at idle. The exhaust travels down stream from both risers through 4" rubber tube. The even bank (the side with issue) has a 12" length of 4" to a 90deg fitting than flows through a 14×4" pipe into a tee, at the tee the odd bank 12" rubber hose joins it. From tee the exhaust travels another 10" into the muffler then out a 6" exhaust at the water line. I've had it apart all the way to the tee and everything is clear into the muffler. I haven't looked at the outlet of the boat yet but I suspect it's clear due to the odd bank exhaust low temperature. I also compared manifold vacuum tests between the 2 engines and they are identical with good vacuum.
 
technish said:
I'm getting that flow of water at idle. The exhaust travels down stream from both risers through 4" rubber tube. The even bank (the side with issue) has a 12" length of 4" to a 90deg fitting than flows through a 14×4" pipe into a tee, at the tee the odd bank 12" rubber hose joins it. From tee the exhaust travels another 10" into the muffler then out a 6" exhaust at the water line. I've had it apart all the way to the tee and everything is clear into the muffler. I haven't looked at the outlet of the boat yet but I suspect it's clear due to the odd bank exhaust low temperature. I also compared manifold vacuum tests between the 2 engines and they are identical with good vacuum.
Click to expand...

technish said:
I'm getting that flow of water at idle. The exhaust travels down stream from both risers through 4" rubber tube. The even bank (the side with issue) has a 12" length of 4" to a 90deg fitting than flows through a 14×4" pipe into a tee, at the tee the odd bank 12" rubber hose joins it. From tee the exhaust travels another 10" into the muffler then out a 6" exhaust at the water line. I've had it apart all the way to the tee and everything is clear into the muffler. I haven't looked at the outlet of the boat yet but I suspect it's clear due to the odd bank exhaust low temperature. I also compared manifold vacuum tests between the 2 engines and they are identical with good vacuum.
Click to expand...
The owner of the boat just started changing everything in sight to try to fix the problem. None of it worked
 
so the outlet from the Tee is 6"?

and the parts changed was driven by the owner who suddenly noticed one of his exhaust hoses was getting hot?
 
Tee to muffler is 4". 6" out of the muffler. The owner said that the 90 deg elbow and the up stream rubber pipe melted on the bad side. I'm not completely sure he changed both sides of the tstat housing, he told me he changed everything. Maybe combustion from excess fuel is happening in the rubber tube? Hard to believe with all the water flow but stranger have happened. Owner said the carb was never rebuilt either, but the ignition components are new.
 
Tee to muffler is 4". 6" out of the muffler. The owner said that the 90 deg elbow and the up stream rubber pipe melted on the bad side. I'm not completely sure he changed both sides of the tstat housing, he told me he changed everything. Maybe combustion from excess fuel is happening in the rubber tube? Hard to believe with all the water flow but stranger have happened. Owner said the carb was never rebuilt either, but the ignition components are new.
 
The tee isn't sized appropriately...but that's a different issue...

If you got that much flow out of the exhaust ELBOW, I'm surprised the exhaust HOSE melted...have you verified the 200 degF temp on the hose with the engine running...That flow is more than adequate to provide adequate cooling...

The t-stat housing only has a single port relief valve...so the normal flow into the exhaust manifolds is split in the upper half of the t-stat housing...the initial thought was the hose from the t-stat housing to the manifold has an issue (internally) but with that much flow I can't see it as an issue....unless the hose only restricts water flow at higher RPM.

If you can't see a 'hot' exhaust hose with the engine running at idle, I'd be inclined to check both hoses feeding water to the exhaust manifolds...if you can't thoroughly inspect the interior of the hoses, I'd change them...given the investment in 'new' parts already, a few feet of cooling hose is a bargain...
 
The exhaust over heats at idle, the water tube supplying the manifold was replaced as well. I'm thinking there's somehow combustion in the exhaust from an excessively rich condition on that bank. Or a partially plugged exhaust hose further down the line that isn't showing on vaccum gauge.
 
If the 'combustion in the exhaust' was occurring, I'd think that would be very easy to hear, even for us in the slightly hearing impaired bucket...and it would be obvious from measuring the exhaust passages in the bottom of the manifold...

The clogged exhaust seems unlikely as was clear thru the tee and the issue is only seen on the even bank and not on the odd bank...

Is the 'hot spot' on the 4" exhaust hose just in one spot or pretty consistent around the top of the hose? (the thought is maybe the elbow casting has an irregularity that messes up the water discharge pattern...if so, then swapping elbows from side-to-side should result in the 'hot exhaust hose' staying with the problem elbow...)

Still baffled at the hot spot given the volume of water measured...may be plausible if the raw water is being aerated....did you use a piece of clear hose to see if any air was being introduced into the cooling water?
 
looks like a lot of flow from the 'lower' opening....what does the flow look like from the other elbow? are the 'new' elbows Crusader or aftermarket?

I haven't had a good look at the crusader center riser elbows in a while....I'm pretty certain the last set of Mercruiser elbows I looked at only had the water outlets on the 'top' of the exhaust ports where the water is dumped into the exhaust stream...
 
I didn't pull the other exhaust. The riser installed is identical to the one removed, same water outlets. I'm not sure if there Crusader. The sides of the rubber tube are getting hot, not the top or bottom at all.
 
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