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4 stroke outboard oil


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Due for an oil change on a few smaller outboards, seems 10 30 is recommended, and there is plenty of that to Choose from, but then there is marine branded oils which were not in stock. They claim to have more corrosion resistance etc.Is it any different or worth paying extra for, I am talking about 2;4;and 10 hp motors, that get used occasionally and mostly at no more than half throttle.

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When it comes to oil, IMHO, it is worth considering how much you can save buying some crap from supercheap over the manufacturers genuine oil.

And how important oil is to the life of an engine.

Just my 2 cents worth, I'm sure there are people that will tell you the $5 saved is worth it,

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my honda 2hp 4 stroke 250ml of 10/30 normal car oil,how can the internals corrode unless the salt water gets in,Which it shouldnt,only the outside can corrode, the only internal which can corrode is the pump housing,waterways etc,oil does not protect those parts,hondas are air cooled so no saltwater internally anyway.

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It is not about the oil quality as such. It is about whether and engine has an oil filter or not. Most small motors do not have filters.
For any engine that has a Filter, you need an Oil with a detergent in it. The Detergent keeps the Particulates in suspension and as the oil passes through the Filter, the particles are removed.
For engines that do not have a filter, you don't want the particulates to be floating in the oil to be pumped around the internals of the engine to attack all the those important little parts. You want the particles to settle to the bottom of the Oil Sump so they stay away from all the goodies in the engine and then when you drain the oil, the particles are removed with the oil.
These kind of Oils are not so easy to come by at the normal places like the Supercheap/Repco's and is often why some Outboard makers have their own brand of oil. Which isn't really their own Oil, it is still made by the main players and they simply rebottle it in their own name. Anyone dealing with small motors, like Lawn Mowers will have these kind of Oils also. Although I have no clue as to the quality of a lawn mower oil when compared to a Brand name Outboard oil.
It is not critical. Any Oil is better than no oil. And by the way, Super Cheap and Repco have some very good oils in their range. Penrite is one of the best brands on the planet and they both have all the main names. They also have El Cheapo oils, but even cheap ones are not that bad these days.

When it comes to 2 stroke Oils, that is a whole nuther story. The are big differences mainly due to the operating temperatures of the engines. Outboards being different to a motorbike for instance. And as there is Air being drawn through the enigine with the Fuel/Oil mix, Anti corrosion additives are very different between the two.
 

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Oil accounts for 40% of the engine cooling in an ordinary car engine. For an air cooled aircraft engine, that could be substantially more. And these are dry sump engines remember. The main difference between the Rotax and the Lycoming  is that the Rotax fluid cools there engine heads, but the Cylinder itself has radial cooling fins.
The other possible is that because the Rotax is an engine specifically made for Home built light aircraft/microlights etc, the fuel used can be ordinary Car type petrol. So the engine will be designed to take a far wider range of Octane rating. Avgas being 100 of course. Overseas, there is another Aviation fuel that can be used in these engines, and I am not completely sure, but I suspect it is a Methanol based fuel. These Fuels cause the engine to run and very different temperatures and so the Oils asked for would need to meet the various Fuel types.

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