Synthetic in the lower unit won't affect engine heat worth a dime. <br /><br />Lower units run cooler than car gearboxes, they are much simpler, and they take a lot less strain than a car gearbox does. With an oil change once a season - which I guess is what most of us do - whwether we go for synthetics or conventional oils ain't gonna make a heap of difference to the life of the outboard.<br /><br />Just MHO.
"OIL THREAD ALERT, OIL THREAD ALERT"!! <br /><br />I WAS JUST GOING TO BED WHEN THE ALARM WENT OFF! <br /><br /> Even though Im a firm believer in synthetic oils in automobiles and about everything else that moves, I would not extend the oil change interval on an outboard engine with synthetics due to the fuel delution issue. If you find the correct wieght in any of the synthetics, you can use it with confindence. It will extend the life of the engine some. Your great great great grandkids will enjoy it, where with conventional oil only your great great grandkids will get the pleasure. <br /><br />As far as lower unit oil, I have allways seen a slight performance increase in the larger outboards with a synthetic gear lube. I think it is mostly due to the oil being thinner, even though it carries the right wieght caracteristics.
No you did not.
Unless I've completely lost it, I think you'll find that the opposite is true.
I agree that this statement is not correct for virtually all substances which dissolve in water. Unfortunately I am correct with salt and this is why you see salt buildups in the water passages where you have the highest cooling water temperature. The salt buildup then gives better insulation between water and aluminium and so higher aluminium temperatures continue the problem of buildup. Cold water flush as long as thermostat opens will flush some of the buildup out.<br /><br />It is to stop this salt buildup that outboard manufacturers limit the thermostat temperatures to such a low figure and the resultant low oil temperature stops (or at least reduces) water being evaporated off from the oil.<br /><br />I am happy to be corrected if somebody has some better information. I am raising the issue because I would like to see public pressure on manufacturers of 4 stroke outboards to have closed circuit cooling systems like on cars at least in the larger motors. This will allow oils to last much longer and not simply be drained out because of water content.
