Wednesday, February 1, 2012

Key West - Have you checked your exhaust elbow recently?

Old vs New exhaust elbows (despite appearances, they are exactly the same size
For those who have been following the blog, you've heard of our steadily increasing engine temperature problem. The engine has been increasing from the usual 80C to 95C  (water boils at 100C). All the usual suspects have been checked and found to be okay (impeller, water pump, strainer, etc.) Hinckley thought the engine ought to be descaled (pumped solution to rid the engine of internal deposits). Finally I placed a call to my long time expert, Brian at McDonnell Marine in Connecticut. He immediately diagnosed the cause to be blockage in the exhaust elbow.

So what is the exhaust elbow and what does it do? All marine engines, both gas and diesel, have an exhaust elbow. It's the point in the exhaust where the engine cooling water is injected into the engine exhaust. The next step is the muffler and then the water and exhaust gases mixture is expelled out the back in characteristic bursts familiar to all boaters.

New elbow - see the injection port, dark rectangle (hole in shadow)
The problem with all this is that the exhaust gases are very hot and even the cooling water is no slouch, around 80 to 90C. Throw in the salt from the ocean and you have a very corrosive environment. Most elbows are made of cast iron, not a particularly corrosion resistant material. That leads to rusting inside and eventually the blockage of the ports where the cooling water is injected - which leads to less cooling water flow and higher engine temperatures as a result. If not attended to, the cooling water will clog completely and the engine will overheat (as your overheat alarm goes off!!) On Fleetwing, I installed an engine temperature gauge so I was watching the temperature increase with concern.

Injectilon port blocked! Overheat, here we come

Today I replaced the elbow and, sure enough, one of the two injection ports were completely blocked with rust debris! I was getting at best half the cooling water flow. No wonder the engine temperature was going up! Most manuals recommend checking the exhaust elbows for blockage every four years. I had gone 10 years! How long have you gone?


Jeny said...

Very nice information..........
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