Blown Exhaust Hose

Hi All,

Out for the first run of the year this saturday, we had been riding for about 5 mins, when the boat filled with smoke, panic panic!! Shuting down the engine we found that the right rubber exhaust tube from the riser to back box had had blown a hole in its self about fist size.

Anybody else ever had this happen? What would cause this? The boat is a 1996 Super Sport Nautique Vdrive with GT40. The hose is original i think, so 12 years old, the other hose still looks good.

Cheers
Rossl

Bird nest in the exhaust? Backfire?

Low water flow can cause overheating of the exhaust. Check your impeller and then the system for blockage. Transmission cooler, strainer, etc.

I agree that it could have been an overheating issue but it might not have been recent. It could have been something that happened awhile ago and caused the hose to get hard and brittle. It could have just let loose now. Was the motor temp ok when it happened? The engine could have been starving for water now. This happened to me last year with my supersport, the impeller pump went bad, and caused the engine to get no water. It ended up warping a couple of valves. I replaced the valves and head gaskets. I also replaced the exhaust hoses while I was at it to be safe.

Its a closed cooled gt40 motor and the temp never got above 160 when running, That day there was a little more white steam coming from the boat than normal, but it was a very cold day. With the hole in the exhaust tube we had to limp back at idle and there was still water getting pushed out the hole at a good rate (Not constant, a burst every few seconds?). I am thinking water flow as we had just fitted a "flush pro" to the boat. Rossl

If the impeller had failed, the closed cooling system would have kept the engine cool, for a bit. But the exhaust would overheat in a matter of seconds.

On a "raw water cooled" engine the raw water pump sucks water up from the lake then pumps it through the engine block. When it exits the engine block it is pumped through the exhaust manifolds (cooling jacket) and the finally dumped into the exhaust itself after the "riser". The cooling water then exits the boat through the exhaust.

On a closed cooling system, the engine block is cooled much like a car engine would be. Instead of a "radiator" there is a "heat exchanger". The closed system circulates its water through the engine block and heat exchanger.

The raw water pump still sucks water up from the lake, then pumps it through the heat exchanger to cool the closed system water. After the heat exchanger the water is dumped into the exhaust, just like the raw water system does. Some systems will cool the exhaust manifolds with the closed system and others cool it with the raw water.

The first sign that your raw water impeller has failed is that the exhaust will get louder due to the lack of muffling that the cooling water would provide. On a raw water system you might notice the rise in engine temperature before the exhaust hose melts, but they would be pretty close.

On a closed system the engine will take a couple of minutes to overheat. That poor rubber exhaust hose, on the other hand, can't handle the extreme exhaust temperatures without a constant flow of water.

Usually such a failure will be accompanied by the unmistakeable smell of burning rubber. If you smelled that then I would say, without a doubt, that your impeller is toast.

If you didn't smell any burning rubber then I might believe that the hose failed for some other reason. I have certainly heard of cases of small rodents making thier home in the exhaust and simply chewing their way through the hose. I would expect that the teeth marks would be obvious, however.

Bottom line: check your impeller. While you are checking it, might as well replace it.

Rod

There was a smell of burning rubber when it went, I thought it was just the hose, it took us 20 minutes to drive back to the dock with the burst hose and water was still getting pumped out of it? i will check the impellar out.

Rossl

it happened to my friends boat yesterday,a brand new x-15 with only 1 hour.It also has a flush pro installed.The flush pro has a check valve but if the thru hull fitting for the garden hose leaks it might suck air into the raw waterpump.
(i,m just guessing here,cause the engine temp was normal 160 all the time)

i towed his boat to a dock and we where able to close the gap with another piece of rubber hose
102 mm wich fitted perfectly.Anyway he was able to drive the boat back across some pretty heavy chop and took it to the dealer.

I did some trouble shooting yesterday and found where the issue is, if i connect a hose to the water pipe feeding left manifold water rushes through and out the exhaust fine, if i connect a hose to the water pipe feeding the right exhaust manifold it takes a lot of strength to hold the hose in and only a trickle of water comes out the exhaust, if i take the right manifold drain plug out water runs through it fine, so there is a blockage between the manifold and riser. So i need to take off the riser, but it is stuck fast, 1/2 inch bolts won't budge. Any body got any ideas of how to get it off? Cheers Ross

PB Blaster and let it sit overnight. When you remove, break it quick with a cheater vs. a slow turn.

Does anybody know the size of the long bolts that hold on the PCM 3.5" short exhaust riser to the manifold. As i think i am going to need new ones once i have this riser off.

Cheers
ross

You can get new bolts and gaskets in a kit from skidim.com or partman.com

I would but i am in the UK and it takes about 7 days to ship from the US to here.

rossl

You are going to HAVE to get new gaskets, and you are going to need a wire wheel or a lot of wire brush to get the old off. The bolts aren't very long, but I do not remember the size; maybe 1"-1.5".

I bit the bullet and Order the gaskets and bolts from skidim $18 worth of parts and $100 fedex priority shipping to get them for the weekend. Worth it not to miss riding ..

rossl

OMG....$100.....that's crazy. I could have missed a weekend for that.

I guess the conversion is in your favor right now though.

The conversion is 2 to 1 so good, but we will spend over $400 dollars on fuel on a weekend so $100 is not too bad in the scheme of it. Also we don't get a very long season here so we have to make the most of it. The guys at skidim where v.good as well.

Rossl