water pipe burst, to much pressure 4.3GL-D

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colliemcc

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I was out on my boat last wednesday and one of the large water pipes burst. I replaced it today and when the rpm is increased the pressure on the pipe also increases. Id say If I brought it up to 3k rpm it would just burst again. Boat was going perfect up until wednesday evening. Does anyone have any idea what could have caused the pipe to burst and now causing the high pressure, in this pipe.

The engine is a 2004 volvo penta 4.3GL-D
The pipe is number 17
in the link attached.
http://www.marinepartseurope.com/en/volvo-penta-explodedview-7744270-26-8546.aspx

Any help will be greatly appreciated

Colm
 
Last edited:
Without seeing your pic I'd say your manifolds and risers are corroded and blocked slowing the water flow out and around the engine, that's where I'd start.
 
Thinking about it now I only blew down the star board manifold, I blew from the end of pipe that goes into the thermostat housing and it seemed frew flowing Ie bubbles out the leg. I will do the other side first thing in the morning.
 
hose #17 in your schematic is the main hose from the raw water pump to the thermostat housing. From there, there is direct feed to the exhaust manifolds ( and via the thermostat into the engine). If the hose is blowing off, there is a serious blockage in the manifolds/ risers.
 
Number 15 in the drawing attached is the water feed from the water pump to the thermostat housing. then the two no 12s head down to the manifolds.
 
GrahamHR said:
hose #17 in your schematic is the main hose from the raw water pump to the thermostat housing. From there, there is direct feed to the exhaust manifolds ( and via the thermostat into the engine). If the hose is blowing off, there is a serious blockage in the manifolds/ risers.
Click to expand...

... or some serious back pressure caused by exhaust gasses getting somewhere they should not be?
 
colliemcc said:
Number 15 in the drawing attached is the water feed from the water pump to the thermostat housing. then the two no 12s head down to the manifolds.
Click to expand...

Yes, sorry for my mistake, hose #17 is the coolant recirculation hose. For it to burst or blow off, it indicates a very high pressure within the engine coolant circuit. A raw water (sea water) cooled engine should have virtually no pressure in there. As the engine warms up, it's a closed system until the thermostat starts to open and allow cool water in.
 
As graham says you should virtually no pressure in the block when running, the sea water pump bypasses an amount of water all the time to feed and cool the manifolds, when the engine is up to operating temp the stat opens allowing sea water to be pumped by the circulation pump through the block and out via the exhaust manifolds and risers, you must have a blockage somewhere to cause the hose to burst or expand like this so I'd be starting from the sea water pump area though the system.
 
Gonna have to wait till next week to pull of the manifolds. As its sitting in the water. The bellow on the port side looks like it over heated/melted so that will be my first port of call maybe a blockage there.....I hope
 
colliemcc said:
Gonna have to wait till next week to pull of the manifolds. As its sitting in the water. The bellow on the port side looks like it over heated/melted so that will be my first port of call maybe a blockage there.....I hope
Click to expand...

I'd also take the thermostat housing off and have a look in there , the 2 cast in hose tails for the hoses that go to the manifolds can get blocked up with rust particles and flakes. On my previous boat I only used the engine for 1 season ( ca 45 hours ) before I fitted closed cooling. The amount of build up in the cast iron thermostat housing after that one seasons use in salt water was surprising, those hose tails were down to around half their original internal cross sectional area.
 
Cheers for all the replies will let you know how I get on, and if anyone else has any ideas feel free to let me know please
Colm
 
Down at the boat here. Took off the thermostat housing. Found a piece of an impellor in it. I also took out the thermostat and ran the engine with no problem brought it up to over 3k rpm.

Then put back in the stat and seems to be building pressure again does not seem to be as bad as before. How much pressure is in that pipe. Like at 3k rpm should Ibe able to ssqueeze it.

Cheers
Colm
 
Anyone got more info taking the boat out this evening to replace one of the exhaust bellows. And to take a look at both manifold conditions.
 
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