NSW
123 posts
I will soon be servicing the Mixing Elbow/Riser and the Exhaust Manifold on my raw water cooled Yanmar 3QM30. The Mixing Elbow is a 5 year old aftermarket stainless steel one and appears to be in good condition externally however i suspect there to be a fair degree of fouling inside. The Exhaust Manifold is the standard 'wet type' that is found on most small marine engines. Again it appears in good condition externally. As to its age i don't know, however it may be original as it is in the original paint that Yanmar put on the engine 30 odd years ago. My intent is to remove the manifold, inspect and clean out the exhaust and water galleries using a Rydlime bath, screwdriver and
hacksaw blade laid flat to get into and clean water galleries of rust and salt build up. For the carbon a chisel and wire brush should be sufficient.
The question i have is how long should a exhaust manifold last? What experiences are other boat owners having with exhaust manifolds and mixing elbows? From information gained by searching the net some 'experts' state that both the mixing elbow and the exhaust manifold should be replaced every 3 years. Mixing Elbow at 3 years sounds plausible but a Exhaust Manifold every 3 years seems way excessive to me. An exhaust manifold for a RW Yanmar 3QM30H is $1150 plus another $150 for gaskets. Though expensive i am prepared to replace this if necessary as the engine is in great condition.
Boat owner experiences and wisdom would be greatly appreciated.
NSW
7757 posts
The exhaust manifold should last forever. The mixing elbow is a different story. Cold water hitting the exhaust is going to always cause a problem. Letting an engine idle with no load will cause a block up. Just be careful where you jam that screwdriver!
