In one of the boating forums I belong to, a well respected contributer and I got into a discussion on engine oils for boats. Specifically, we were discussing a 10 year old Mercruiser 4.3 engine. Here is what he wrote:
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Merc racing and the NHRA drag race crowd ran into issues with diesel oils some time ago. The Delvac’s, Rotella-T’s, and Dryden offerings all use a heavy metal additive, usually Zinc. Diesels as you know suffer from fuel contamination into the crank case during warm up. The solution is Zinc to provide deposited lubrication upon the lower cylinder walls to prevent piston skirt scuffing as the crank passes through BDC. This finite additive also gets into the combustion chamber and detonates along with the fuel charge. In a lite to moderately loaded gas engine as installed in say a fleet delivery truck, the additive tends to stay in the crankcase.
Marine application was a different animal. As the offshore racing crown attempted to use the Shell and Mobil diesel offerings, their knock sensors were mapped showing timing reduction at moderately high to WOT operating conditions. The drag race guys just melted the top rings as they were running close to 17:1 compression ratios. The knee jerk reaction was to blame the fuel.
Combustion chamber temperatures in a marine engine operate somewhere in the stratosphere as compared with an automotive application. After altering fuel blends and talking with some of the top researchers in the industry, it was suggested that migration of the Zinc into the combustion chamber was creating a perfect storm of “glowing glitter” which caused pre-ignition and initiated the knock sensors to back out total ignition timing. Unless you have the hand held plugged in during a high speed run, a boat owner would never know it happened. I run a 496-HO, and can see the same thing happen if I attempt to run regular fuel, of even mid-grade in late July when the temperature is high and the air saturated with moisture.
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So, what do you all think? Most on here recommend diesel oils for boating. Modern diesel oils have less Zn than the oil available 10 years ago when this particular engine was new. Is this a plausible argument?
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Merc racing and the NHRA drag race crowd ran into issues with diesel oils some time ago. The Delvac’s, Rotella-T’s, and Dryden offerings all use a heavy metal additive, usually Zinc. Diesels as you know suffer from fuel contamination into the crank case during warm up. The solution is Zinc to provide deposited lubrication upon the lower cylinder walls to prevent piston skirt scuffing as the crank passes through BDC. This finite additive also gets into the combustion chamber and detonates along with the fuel charge. In a lite to moderately loaded gas engine as installed in say a fleet delivery truck, the additive tends to stay in the crankcase.
Marine application was a different animal. As the offshore racing crown attempted to use the Shell and Mobil diesel offerings, their knock sensors were mapped showing timing reduction at moderately high to WOT operating conditions. The drag race guys just melted the top rings as they were running close to 17:1 compression ratios. The knee jerk reaction was to blame the fuel.
Combustion chamber temperatures in a marine engine operate somewhere in the stratosphere as compared with an automotive application. After altering fuel blends and talking with some of the top researchers in the industry, it was suggested that migration of the Zinc into the combustion chamber was creating a perfect storm of “glowing glitter” which caused pre-ignition and initiated the knock sensors to back out total ignition timing. Unless you have the hand held plugged in during a high speed run, a boat owner would never know it happened. I run a 496-HO, and can see the same thing happen if I attempt to run regular fuel, of even mid-grade in late July when the temperature is high and the air saturated with moisture.
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So, what do you all think? Most on here recommend diesel oils for boating. Modern diesel oils have less Zn than the oil available 10 years ago when this particular engine was new. Is this a plausible argument?
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