What could have caused this..??

[moresparks]

Hi, as can be seen by the photo I have a split in the exhaust hose.
This happened suddenly and without warning filling the bilges with water and spraying seawater everywhere.
This is the rubber connecting hose (Volvo Penta part number 834871) that connects the exhaust manifold to the sterndrive exhaust pipe. This is a true blue Volvo part and not aftermarket and is only 2 to 3 years old.
At first I thought it may have been the hose clamp fitting but that was positioned quite high up.
Was I unlucky? Or should these now be changed at the same time as the bellows etc.
The conditions weren’t bad with only a slight chop and just cruising around 20knots so only minimal vibration.
Puzzled!!!

 

[stelican]

Could be poor alignment between elbow and exhaust horn causing a hard spot

 

[BruceK]

was there excessive rust on the lip of either the exhaust elbow or the exhaust pipe below that might have started the tear? The lip seems liable to rusting up.
Any sign of heat damage that may signify partial blockage in the elbow?

 

[moresparks]

Many thanks for responding.
The exhaust alignment has never ever been perfect and the exhaust manifold is brand a brand new stainless steel “Hi-Tek” as the original manifolds for my AQ171c’s are no longer available but these new manifolds are far more efficient and run cooler with no rust anywhere.

 

[BruceK]

Stelican may have nailed it then, but you may just have been unlucky in as much as I have heard of drive bellows tearing within their service interval too. They are a service item but I dont know the interval tbh. Keep a spare and see how it goes.
At a massive stretch here, the only other thing I can think of that may account for it, and it is a reach, is excessive exhaust back pressure causing higher temps, possibly? I'm sure someone else can chime in on that account and any other ideas.

 

[Freebee]

The last time I had one fail it was because the water pump impeller failed causing the exhaust rubber to overheat and soften, have you checked your impeller lately??

 

[moresparks]

Impeller working fine as witnessed by the volume of water pumping into the bilge even at tick-over. Temperatures also fine.
I am thinking that maybe I may have been too enthusiastic in cleaning the engine compartment in the past and some chemical has landed on the exhaust hose causing a softening of the rubber. On closer inspection there are other minor cuts / splits where the hose clamps are.

 

[BruceK]

Are you over tightening the clamps or reusing old clamps?

Edit, as on mine getting the clamp off requires a lot stretching it out which may buckle it ever so slightly but enough to cut when retightened