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Vortec engine overheat on cowhorn bend

M

mtrigger

Member
I have a Vortec 4.3L which replaced VP AQ205A. The original Volvo Penta raw water cooling pump failed and replaced by http://www.keypart.com/stock/857451. Since replacement the top of the cowhorn bend on one side only after the exhaust rubber gets hot, the other side does not. The manifold and risers both sides remain barely warm. The overheat is confined to the cowhorn bend and to some extent the rubber as previously stated on one side only. I have removed both manifold and riser which appear unblocked. The riser design is the central exhaust flow with the cooling water rifled around the outside. It appears there is insufficient water pressure passing through the rifleing in the riser to create a tube of water to wrap itself around the exhaust gases. The impeller in the replacement pump is clealy smaller than the original Volvo Penta part. Any opinion very welcome. Many thanks.
 
Clearly smaller is an issue. The flexible impeller style pumps require a very specific fit to their housing. Another issue to consider is... When you removed the old impeller, was it intact? If not did you find all the pieces? Pieces larger that about 1/16 of an inch missing from the impeller and not found is recipe for problems.
 
Thanks Capn Bob. So far I have replaced - impeller, water feed pipes to manifolds and to/from circ pump, thermostat and new housing. Leg off and camera inspected waterways - all clear. I guess if the rifleing in that riser is no longer as narrow as it was perhaps their is no longer the resistance available to create the vortex effect. I am going to replace with another type where the cooling water exits from the top of the riser bore so instead of completely enveloping the exhaust it drops down over it so to speak.
 
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