What is premix?
Premix is mixing 2-stroke oil with the gas in the gas tank to assist with lubrication of the apex seals.
Because 2-stroke (in general) is designed to be burned cleanly without deposits. Unlike 4-stroke that you use in during oil changes, which is not designed to be burned.
This gets a bit more vague when answering. The short answer is as noted, to assist with apex seal lubrication. But do we need it? That's a tougher question to answer with facts. Some people swear by it, others do just fine without it. Series1 RX-8s have 2 injectors pointing at the side seals, Series 2 adds a center injector to help with lubricating the center of the apex seal. Mazda added this, so they must have found excessive wear in the center of the apex seal, so it's circumstantial evidence for the need to premix. It's hard to say if this will save your engine from apex seal wear failure though. About the only confirmed difference premixing really makes is that the carbon buildup inside the engine appears to be "softer". In theory, makes it easier to clean, and if it comes off it won't come off in dangerous flakes that could cause carbon lock.
Which premix to use?
Lots of debate here too. There are lots of options, and not all of them are even oil. The list below is ordered from most ideal at the top, least ideal/not recommended at the bottom.
- Idemitsu Premix is generally considered to be the best out there. The only draw back to it is accessibility in that you have to order it, and there are minimum order quantities. Often a member here will order a larger case and split it with locals, making this a bit easier, but it's also usually a 1-time thing.
- Amsoil Saber Pro is highly regarded, and a bit easier to get than Idemitsu.
- Pettit Protec R is from a well established rotary vendor, and is probably comparable to the Amsoil above. The problem is that the testing and 'evidence' provided don't mean anything, since none of the test conditions are what the 2-stroke sees inside a running engine.
- JASO FC and ISO oils basically other oil brands of the same type and grade as the items above. May be easier to obtain than those.
- TWC-3 Oils are usually easy to find, however it's not likely that you are doing much good with them. Not much harm, but small engines that require this type of oil can fail due to lack of lubrication from it, so it might not be sufficient for us. One explaination from RX8Club forum member 'Emery':
I think some things should be clarified, after several PM's between me and STEALTH and doing some online research on TCW-3. It is definitely designed to be burnt and fully combust without leaving any residue or ash (if it is a synthetic ashless oil). It is made WITHOUT any metallic additives, as it is meant to burn ashless it does not contain any.
While it probably wouldn't do any harm to the car (besides the catalyst), the problem with TCW-3 lies within it's lubricating capabilities. It is not as good as an oil at lubricating as a ISO or JASO FC certified oil is. TCW-3 is an oil that is not good enough to lubricate snowmobiles and motorcycle engines, and has lead to failure to those engines that TCW-3 oils were used in. Not because the oil itself caused the failure, it just didn't serve it's purpose in lubricating the bearings and engine parts that needed lubricity, hence the failure.
So what I'm trying to get at is... TCW-3 oils suck as a lubricating oil. A JASO FC and ISO oil would do a much better job. TCW-3 premix is not the worst thing you can put in the car though, it shouldn't harm it, and it should lubricate some what, but it just isn't the best lubricant we would want for our engine; we would want to get the best we could in there. I just wanted to clarify this and explain some of these details, so that people using TCW-3 as premix don't get scared and think that they have potentially harmed their engine by using a oil with metallic particles (not true) that isn't meant to combust in their car (not true as well).
If you were using TCW-3 oils as I was, you should definitely switch to something else like idemitsu or any other 2-cycle oil JASO FC or ISO rated. This is one long assss thread, and reading through it is a pain, but if one does so you would find how contradicting a lot of the information is. I just wanted to make it easier for some people, and so that others don't make the same mistake I and many others have made.
- Marvel Mystery Oil (MMO) is common, and easy to obtain. Some people swear by it, others denouce it totally. The people that love it can't prove that it does anything good, and the people that say that it is worthless can only point at it's cleaning agents as being a problem, which doesn't even sound like it's that big of a problem. All in all though, it probably doesn't have much lubrication compared to some of the other options above, so it could be considered to probably be on the same level as TWC-3. I.e., not doing much, or if anything, perhaps just some carbon removal (which isn't bad).
- Lucas Upper Cylinder Lubricant (Lucas UCL) is a non-oil you can find out there, but we can't recommend it. We can't prove that it causes any fuel filter problems, but for some unknown reason it shows up in a significant percentage of fuel filter problem threads (>2 in 3 threads at a guess). There is some suggestion that this is because the fuel actually starts solidifying / sludging with Lucal UCL in the tank. Nothing proven to back this up, but the rate of Lucas UCL in fuel filter problem threads is hard to ignore.
How much premix?
The standard amount is about 1oz for every 2 gallons of gas. Some people go 1oz for every 3 or 4 gallons, and some go for 1oz to 1 gallon. 1oz for 1 gallon is getting on the high end though, so don't just use that to use it. Dig into why you want that much. One of the common reasons for going to 1oz to 1 gallon is for a track day. Lots of heat means a bit better lubrication could be a good thing in the end. Note that these values are for how much fuel you are putting into the gas tank. So if you are filling up at halfway and adding 7 gallons, then about 3.5oz is ideal. If you never fill till the light comes on, then around 6.5oz is more accurate. Some premix containers come with a measuring method built right into the top, otherwise it might be useful to find some small plastic containers of the ideal size to keep several on hand. I lost them in a prior move and haven't replaced them, but for a while I was using four 6oz bottles that were originally intended for hair products. Clean them out thoroughly, let them dry, fill ahead of time, and keep tucked in the car to easily add when I fill up. If you opt for this and don't use glass bottles, I'd recommend replacing the bottles periodically, maybe every 6 months. Most plastics aren't of a grade that is designed to hold petroleum products, and it will start to break down from the inside after a while.
Managing oil bottles can be a pain?
If you go for the Idemitsu, it comes in a handy container that allows you to easily transfer a specific amount of oil into a separate section within the container top that is easily visible and marked with volume indicators, and then only pour the contents of that section out. Very easy to use. Anything else, will not be that easy. The best recommendation is to find small 8-12ox containers to store oil in as 'doses'. Keep in mind though that if you use anything plastic, that you only want to carry a week or two of oil in them at most. Petroleum products can disolve and degrade most plastics, and you don't want to carry a years worth and one day find that they all leaked out all over your car. Glass is a more stable option, though breakable.