....................... finally revealed.
Ever since we purchased the boat new, I've worried about leaking water back into the cylinders of the Yanmar 2GM20F. The reason for the worry is the location of the mixing elbow situated ABOVE the engine
. All we'd need to have is the separation wall between the cooling sea water and the hot exhaust gasses spring a leak, and it's all over. Just need the fat lady to sing. Cold sea water is bad enough (corrosively speaking), but heat it up ........... I don't even want to think about it . I know cast iron is more corrosion resistant than mild steel, but the consequences of a perforation in the separation wall would be of biblical proportions indeed.
The below picture shows how the elbow sits above the engine.
This next picture shows a new mixing elbow attached to the riser piece which is in turn attached to the exhaust manifold. You can see how a pin hole perforation could allow sea water to dribble down through the riser and into the exhaust manifold and then ........................ well, you just don't want to go there :cry:.
For that reason, I remove the elbow every two years to inspect and clean and every four years, replace it . Perhaps a tad expensive at $382.35 (with taxes) for the last one, but better than the alternatives.
This time, in order to see how closely I was courting disaster, I decided to section the last elbow removed and a previous elbow which was laying around.
The below picture shows an earlier elbow which had been cleaned and then tossed to the rear of a shelf rather than put it back into service. It was sectioned using my favorite cutting oil, straight liquid soap detergent. Makes for an easier clean up and no, the red rust colour on the hot exhaust side is not due to water leakage into the exhaust passage. Just the result of washing the elbow in water and letting it dry. Notice the thickness of the wall separating the water from the gas passage. This is after about four years of service. Lots of metal remaining.
On to the most recent elbow removed, still in the original dirty condition. This was cleaned two years ago and is again REALLY dirty. Notice the carbon buildup restricting the gas passage. Notice the carbon buildup just where the sea water mixes with the hot exhaust gasses. Notice that it's a miracle the engine can still run. I didn't notice any problem with the engine running full throttle (3600 RPM) last season nor was there any sign of overheating displayed on the VDO engine temperature guage. And it certainly isn't the result of clean living on my part.
The one thing I do know for sure, the carbon has got to be due to the 138 F air inlet to the engine. It's the result of storing the engine in a shoe box as shown below.
So, after this little excercise, I find myself with one less thing to worry about on the boat. Now, to replace it with something else to worry about.
Ever since we purchased the boat new, I've worried about leaking water back into the cylinders of the Yanmar 2GM20F. The reason for the worry is the location of the mixing elbow situated ABOVE the engine
. All we'd need to have is the separation wall between the cooling sea water and the hot exhaust gasses spring a leak, and it's all over. Just need the fat lady to sing. Cold sea water is bad enough (corrosively speaking), but heat it up ........... I don't even want to think about it . I know cast iron is more corrosion resistant than mild steel, but the consequences of a perforation in the separation wall would be of biblical proportions indeed.The below picture shows how the elbow sits above the engine.
This next picture shows a new mixing elbow attached to the riser piece which is in turn attached to the exhaust manifold. You can see how a pin hole perforation could allow sea water to dribble down through the riser and into the exhaust manifold and then ........................ well, you just don't want to go there :cry:.
For that reason, I remove the elbow every two years to inspect and clean and every four years, replace it . Perhaps a tad expensive at $382.35 (with taxes) for the last one, but better than the alternatives.
This time, in order to see how closely I was courting disaster, I decided to section the last elbow removed and a previous elbow which was laying around.
The below picture shows an earlier elbow which had been cleaned and then tossed to the rear of a shelf rather than put it back into service. It was sectioned using my favorite cutting oil, straight liquid soap detergent. Makes for an easier clean up and no, the red rust colour on the hot exhaust side is not due to water leakage into the exhaust passage. Just the result of washing the elbow in water and letting it dry. Notice the thickness of the wall separating the water from the gas passage. This is after about four years of service. Lots of metal remaining.
On to the most recent elbow removed, still in the original dirty condition. This was cleaned two years ago and is again REALLY dirty. Notice the carbon buildup restricting the gas passage. Notice the carbon buildup just where the sea water mixes with the hot exhaust gasses. Notice that it's a miracle the engine can still run. I didn't notice any problem with the engine running full throttle (3600 RPM) last season nor was there any sign of overheating displayed on the VDO engine temperature guage. And it certainly isn't the result of clean living on my part.
The one thing I do know for sure, the carbon has got to be due to the 138 F air inlet to the engine. It's the result of storing the engine in a shoe box as shown below.
So, after this little excercise, I find myself with one less thing to worry about on the boat. Now, to replace it with something else to worry about.
