i use lucas semi synthetic.
just keep in mind that the cheaper 2 stroke oils are designed for yard equipment (trimmers and such) and marine 2 strokes, engines that arent don't get above 10,000rpm, ever. our little engines can reach in excess of 18000rpm, a quality oil is needed to make sure it lasts as long as it should.
as for switching between conventional, semi synthetic, and synthetic, it doesn't really matter. there is so much false info on this subject, not just in 2 strokes but in automotive too. i always hear that if you mix them "bad things will happen" but nobody can ever say what or show pics of it. the truth is synthetics have a modified molecular structure, basicly instead of the atoms in the molecules being in a clump they are in a string. what happens with oil is when it breaks down on a molecular level atoms break away from the molecules changing the structure of the oil, and those atoms are what form sludge. a synthetic oil is a much stronger molecular structure and resists breaking down better because of the changed molecular structure. basicly what im trying to get at is its really all the same thing, synthetic oil isnt completely man made in a lab, it still comes from crude, really its just refined better.
Basically correct but it's also the additive packages that go into the oils that make the difference. The advice is generally that you should not mix synthetics with others in case of problems of compatability not just between the base oils but also the additives and the risk of degrading these additives from doing their job correctly. Some basic info for you.....
What’s in the stuff anyway?
2-stroke engine oils, like most other engine and gear lubricants, are composed of base oil plus an additive package. The additive package can be as simple (only one or two components) or as complex (multiple components), depending on the requirements of the oil.
Base Oil Types
Base oils compose from 50% to 95% of the total weight of the 2-stroke engine oil. They fall into 2 general categories: synthetic and petroleum based. There is a third category, vegetable, I will discuss later. Since synthetic oils are manufactured from petroleum, there has been a lot of litigation flying around about what really constitutes a ‘true synthetic’ oil in the last several years. There is no universally accepted definition for synthetic oil. Each manufacturer is free to label their product ‘synthetic’ by whatever rules the manufacturer chooses. The API (American Petroleum Institute) has defined base oils into 5 different grades or groups rather than use the terms synthetic and conventional (petroleum). The groups are classified by quality of their VI (viscosity index). The VI is a relative measure of the base oil’s ability to not thicken at low temperatures and not thin out at high temperatures. The higher the VI number, the more resistant the oil to changes in viscosity as its temperature changes. Perfect base oil would have no viscosity change at all with temperature change. Some silicone-based oils have extremely high VI, but, unfortunately, they are terrible metal lubricants, so they can’t be considered for engine lubrication. The higher the API group number, the higher the VI number. Most, if not all, high performance 2-stroke oils are manufactured using API group III and IV and occasionally group V base oils. GroupIII (hydrocracked/hydro-treated petroleum oils) are used in non-synthetic and synthetic blends and Group IV (VHVI and PAO synthetic oils) are used in full synthetic and synthetic blends. Group V (Ester synthetic base oils) is rarely used because of their expense and they do not mix easily with gasoline and they are not compatible with some other oils. There are a number of advantages to using synthetic base oil in addition to the better VI. Synthetics have a much higher flash point than petroleum base oils.
Synthetics will not decompose as easily at high engine temperatures as petroleum. The engine stays cleaner because less varnish deposits on the power valves, ring lands and piston crown. They also transfer heat better than petroleum-based oils. In summary, it’s fair to say synthetic based oils (with the correct additive package) will out perform their petroleum-based cousins at extreme loads/temperatures. I mentioned a third category of base oils earlier, vegetable or Castor (not Castrol, that’s a manufacturer) bean oil. This oil is derived from pressing oil out of castor beans and distilling it. ‘Bean Oil’ as it is often referred to, has some very unique characteristics; some very good, others not so good. The good is that it is an excellent lubricant. It seeks out hot spots in the engine and clings to those hot surfaces much better than petroleum type oils. The bad is that it does not mix with gasoline easily and it burns ‘dirty’ (excessive carbon/varnish deposits). In the early 70s, before power valves were used, castor bean oil was very popular in racing 2-strokes. Now that power valves are common and we have improved petroleum and synthetic oils, castor bean oil is seldom used anymore. Several companies still market it in the form of a degummed castor oil for racing applications only. It should be avoided for recreational use unless you enjoy tearing your engine down for a top end cleanup fairly often. Several manufacturers formulate their oil with castor bean oil as an additive (antiwear agent) rather than base oil. They blend it with their petroleum and synthetic base oils. When castor bean oil burns, it has an unmistakable ‘sweet’ smell.
Additives
If science could develop a base oil that would not thermally decompose (burn) until 1600 deg/f and not change in viscosity for –40 to 600 deg/f and not pollute the water or air, we would not need any additives in the base oil. Wouldn’t it be nice if all the oil collected in the expansion chamber body stayed in the same pristine state it went into the engine? We could simply recycle it. Well this isn’t going to happen in our lifetime (sorry, not even you younger guys will ever see this). Lubrication science is just not there yet. Additives are combined with the base oil to fix certain faults with the base oil or stretch the limits of the base oil in some cases. Additives are complex chemicals that account for most of the cost of a bottle of 2-stroke oil. Additives for 2-stroke oils fall into several general categories: Detergent/Dispersants, Antiwear agents, Biodegradability components, and antioxidants. Since the lubricating oil must burn as part of the combustion process in a 2-stroke engine, the residue resulting from this combustion process must be swept away after each firing stroke. If not, the residue (varnish, lacquer and other heavy hydrocarbon compounds) would build up and plug the exhaust port and stick the rings and power valve(s). Detergents/dispersants must be added to the oil to prevent this problem. The two types of detergents/dispersants most commonly used in 2-stoke oil formations are Ashless and Low Ash. Medium Ash and High Ash detergents are not used in 2-stoke oils. Ashless detergents are used in low temperature applications such as TCW3 oils where the ring land temperature is held below 300 deg/f. These detergents work well in engines where an excess of cooling capacity is available and power valves are not used. Ashless detergents are manufactured form organic nitrogen compounds (Hydrazine) instead of heavy metal compounds; therefore, they produce no ash as they are burned away. This is where the name “Ashless” comes from. Oils containing this type detergent have a characteristic Ammonia odor. Ashless detergents were used in the first generation of Bombardier XPS engine oil. The formulation was later changed to a low ash type detergent because of the higher temperatures generated by the 787 engines. Low Ash type detergent/dispersants are used in most API-TC, Jasco FC and ISO GC certified 2-stroke oils. These oils are designed for air-cooled high performance engines that operate under severe load/temperature conditions. Low Ash detergents can keep the deposits to a minimum at ring land temperatures as high as 400 deg/f. These detergents are manufactured from compounds of Calcium and Magnesium (heavy metals). After these compounds (Calcium Phenate or Magnesium Phenate) do their job, they burn away, forming a heavy metal salt (ash) that is swept away during the normal combustion process. Hence, this is where the name Ash-type detergent comes from. Ash type detergents depend on the higher combustion temperatures (787 and 951 engines) to keep the resulting ash swept out. Therefore, the use of these high performance oils in outboard or other mildly tuned 2-stroke engines is not recommended. Some manufacturers are using a combination of detergent types (Ashless and Low Ash) to provide a broader range of uses for their oil. It is important to note that oil designed to meet TCW3 specs. only (Ashless) will not protect an engine requiring API-TC (Low Ash) type oil. The converse is also true. Using a Low Ash oil in an engine designed for an Ashless type oil only could result in fouled plugs and gummy combustion chambers. When 2-stroke oil is kept in its temperature limits, it provides an adequate protective film between all moving parts. When that maximum temperature is exceeded, the oil film breaks down and usually seizure occurs unless another line of defense is added to the oil mixture. These are the Antiwear agents. These Zinc compounds (Zinc Dithiophoshate) flow in with the oil and are never used unless the base oil breaks down. If the base oil breaks down, they form a protective barrier between the moving parts (usually piston skirts and cylinder walls).
Since all 2-stroke engines partially burn and expel their lubricant in the exhaust, the resulting exhaust residue must be rendered harmless to the environment (air, water and land). All 2-stroke oil intended for marine use and many intended for land recreational use contain Biodegrading agents. These complex chemical compounds allow the microbes found in water and in the soil to consume the hazardous chemicals and oil from the exhaust as they fall in the water or on the ground. These Biodegrading agents do nothing for the performance of the oil (sometimes they even hinder it), but they help assure us that 2-stroke engines will be around for a while. As you can see, 2-stroke oils are a mixture of many different complex chemicals with base oil. Each specialty chemical has a job to do. Care must be taken to assure that these different chemicals detergents/dispersants, Antiwear agents, and Biodegrade agents) do not react or interfere with each other or otherwise impair the function of any other additive. Antioxidants are chemicals that reduce the chance of reaction between the various additives in the oil mixture. They effectively extend the ‘shelf life’ of 2-stroke oils.
