Strange Restrictor in Cooling Bypass Hose

[dpapa1911]

2001 Volvo Penta 3.0 GS. Purchased the boat three years ago. Had the water circulating u-shaped hose burst a couple weeks back. Found there was a piece of an old impeller vane stuck in what looks to be some kind of restrictor device within the bypass cooling hose. Removed the vane and ran motor. I notice the replacement u-shaped water circulating hose is swelling a bit at idle and grows larger when increasing throttle. Unhooked the bypass hose, removed the strange restrictor device, reconnect, run engine. Water circulating hose no longer swelling at all regardless of throttle speed. Engine temp and all vitals look good. I’m thinking water circulating hose has been swelling since I got the boat, and once vane stuck in the restrictor hose pressure became overwhelming and burst.

Question is has anyone ever seen such a restrictor device in a bypass hose? Genuinely baffled as to what the purpose would be when it clearly causes enough pressure to swell circulating hose while operating. Restrictor looks pretty crudely made therefore doubt was from factory and can’t find it on any engine diagrams. I’m thinking I will just run the boat with it removed.

Pictures show swollen circulating hose at idle while restrictor device was in place, location of the restrictor device within the bypass hose, and some pictures of the restrictor device once removed from bypass hose.

Interested in any information on this. Thanks.

 

[itsathepete]

I'm not an expert on this setup but perhaps someone added the restrictor to force more water through the exhaust manifolds to keep them cooler. Older designs and mentality was to have lots of flow through exhaust manifolds to keep them cool and prevent damage to rubber parts and keep engine bay temps down. This was found to cause condensation of exhaust water vapor within the manifolds dripping back down to hot exhaust ports causing exhaust valve corrosion and damage. Newer designs have less flow until thermostat opens and keeps manifolds warmer preventing condensation. The bypass allows extra water pumped from the impeller to exit without creating too much pressure. However, the thermostat housing could have a blockage in the small orifice to the exhaust manifold, causing the manifold to run hot, which could be why the bypass restrictor was installed. I would remove the thermostat housing and check for any blockages to make sure.

 

[Scott Danforth]

someone butchered your cooling system.

suggest you return it to stock

 

[dpapa1911]

I'm not an expert on this setup but perhaps someone added the restrictor to force more water through the exhaust manifolds to keep them cooler. Older designs and mentality was to have lots of flow through exhaust manifolds to keep them cool and prevent damage to rubber parts and keep engine bay temps down. This was found to cause condensation of exhaust water vapor within the manifolds dripping back down to hot exhaust ports causing exhaust valve corrosion and damage. Newer designs have less flow until thermostat opens and keeps manifolds warmer preventing condensation. The bypass allows extra water pumped from the impeller to exit without creating too much pressure. However, the thermostat housing could have a blockage in the small orifice to the exhaust manifold, causing the manifold to run hot, which could be why the bypass restrictor was installed. I would remove the thermostat housing and check for any blockages to make sure.

Thanks - yea, we initially pulled the tstat housing off and looked for blockages thinking it must have been an impeller piece, but housing was all clear. Boiled tstat to confirm function and was good to go.

someone butchered your cooling system.

suggest you return it to stock

Yup I removed the restrictor and seems to operate just fine and the bulging cooling hose is cured. Just wanted to make sure there wasn’t some reason I couldn’t think of that it was supposed to be there or that it was like that from the factory (which seemed unlikely given I couldn’t find it on any diagram and how crudely machined it was).

 

[Scott Danforth]

remove the added stuff from the cooling system and return the system to stock.