Oil Talk - Good Brand / Bad Brand, etc.

[evannadeau]

I'd like to hear what everyone is using for 2T mix oil these days, as I'm about ready to pickup some more. I've nearly always run the Motul kart-specific 2T oil, but I've heard that other people have been having really good luck with other oils.

[JasonL]

For Rotax, the Rotax-branded oil is spec., so running anything else on a race day technically risks a DQ. For our karts I've been running Amsoil to save a few bucks since we moved to Rotax, but now that Carson is seeing podiums more regularly, have moved to Rotax on race days as I don't want to have to explain to him why he's been DQ'd.

Any objective evaluation of alternatives is going to be challenging because any suitable 2-stroke oil will be good enough that none of us will ever see a difference during the runtimes that our motors will have between teardowns. Even if something did show in an engine it would be hard to say that it was due to lubricant performance, given limited sample size.

This is made even more difficult because there isn't a third-party standard for a substitute oil to be certified against. It's not like the automotive industry, where a manufacturer says "use an oil meeting SAE ABC123 standards", Rotax says "use our oil, that's it" (arguably, a violation of Canadian competition laws).

Available technical information on oils is limited as Rotax (for example) doesn't want to share anything about their product that they don't have to, and proper oil testing/certification is expensive. I've had a few conversations with our lube PQ folks over the years where they've told me that we're sure that Product A meets Spec X, but we don't say so on the bottle because certification against that standard is incredibly expensive, and we don't think the market is big enough to justify the costs.

In short, my advice would be:

1. For races, use what is required unless you're comfortable risking a DQ.
2. If you want to save some money, read as much as you can about the 'recommended' lube, and find something whose specs are very similar and is advertised for use in similar applications.
3. If you want some sort of edge from a higher-performance lube - that will be very tough. What you'll find in documentation is likely to be of much value. Regardless, impact given how our motors are running is likely to be unnoticeable. I struggle to think of a reason to pay more than one would on the prescribed product.

[evannadeau]

Thanks for the response, JasonL. In the VLR class, both fuel and oil are open at the moment, so I was thinking of going for something more economical than what I have been running. Considering we are running a 25:1 mix ratio, an oil formulation that handles the RPMs yet is a bit more affordable would be nice.

[John Kwong]

Hi Evan,

I tried the Bombardier equivalent of the XPS oil but it was for snowmobiles. It didn't like being used at 25:1 and left gummy deposits in the carburetor. I would recommend staying with the Motel 800 and buy the 4L jug on Amazon which you can get for about $95. It burns clean and mixes well at the larger amount of oil that is used for VLR.

John K

[evannadeau]

Thanks John, that really helps a lot. I've used that 800 before without issue too. I'll grab a jug from Amazon.

[JasonL]

With Amsoil 2-stroke oil available at my local Canadian Tire, it's a no-brainer for me.

[evannadeau]

Thanks, Jason L.

I've been looking at the specs of various oils as part of this discussion. Due to its lower flashpoint, I would offer a word of caution about Amsoil for 2-stroke kart engines. When things get very toasty, Amsoil may flash off early and not provide enough lubrication.

After reading about the specs of these oils, I'll stick with the Motul. I hope this little chart helps others.



Flash Point

Code: Select all

Motul Kart:                256.0 °C / 492.8 °F  -  Designed for up to 23,000 RPM
Motul 800 Road Racing:     274.0 °C / 525.2 °F
Motul 800 Motocross:       252.0 °C / 485.6 °F
Amsoil Dominator Racing:   94 °C / 201 °F
Amsoil Interceptor:        94 °C / 201 °F
Rotax Kart:                "> 200 °C"  /  392 °F
Maxima Premium 2:          136 °C / 276 °F

[JasonL]

Evan,

Flash point indicates the temperature, above which there is enough vapour created by the substance to ignite (The temp. above which a lit match becomes a danger). Gasoline's is about -40C, so will ignite just about any time. Diesel is about 40C, so if you drop a match into diesel, it extinguishes.

Flash point, at best, is a poor indication of high-temp protection as it doesn't suggest what has evaporated, what remains as a liquid, or how much of either has happened.What is of more value are the viscosity at 100C and viscosity index of the lubricants.

Were you able to find a spec sheet for the Rotax oil? I could not, but found info for Motul and Amsoil, and would say that if you’re concerned about high temp protection, Amsoil seems a better choice. I've attached a graph, while not to scale, illustrates this.

The relevant available numbers are the viscosity at 40C and 100C and viscosity index.
When looking at the two oils, the Motul is 'thicker' at both 40C and 100C than the Amsoil, so one might suggest that it provides better protection throughout. The problem is the rate of decline of the viscosity through that heat range. The Motul has dropped 118 points, while the Amsoil has dropped 1/5 that amount. The Amsoil is dramatically better at retaining viscosity under temperature - which is shown in the higher (better) viscosity index number for the Amsoil.

If you draw the line of viscosity for an oil through the temp range, the line is straight (the viscosity on the Y-axis is logarithmic, so 60 isn't twice as high up as 30, for example). What this means is that the two lines intersect soon after 100C, and the Amsoil will be more viscous at high temperatures than the Motul. I'd love to see the numbers for the Rotax oil, if anyone can find them.

Amsoil Motul
Viscosity @40C 30.7 135
Viscosity @100C 6.5 16.9
Viscosity index 172 136

The effect of temperature on oil viscosity is very poorly understood. A few years ago, I had someone at the dealership argue with me when I asked them to put 0W oil in my car. He told me it didn't provide adequate protection vs. the 5W they wanted to use because it was a 'thinner' oil. The thing is, it's only thinner when it's cold (which is what one wants to get the oil flowing through the engine more quickly). The first number in a multi-weight oil denotes the cold-temp viscosity and the second the high-temp viscosity. A 0W40 and 10W40 oil will both have a similar viscosity at 100C (because they are both 40s), but the 0W will be much thinner when cold (good) and thicker above 100C (good), as the lines intersect.

In short, if available, ALWAYS USE THE 0W GRADE OF MOTOR OIL FOR YOUR CAR.

[evannadeau]

Fantastic information, thanks for sharing. I love putting the science behind this stuff. Now I have no idea what to use.


The specs I was looking at from this Rotax Webpage:
https://www.rotax-racing.com/products/f ... %20concept

Was this document:
https://www.rotax-racing.com/assets/upl ... OIL-GB.pdf


Viscosity, kinematic: 189 mm²/s @40°C

[JasonL]

Ya. Back to my earlier point about not much info being available.
I had found the sheet you linked, but that was a safety document, not a spec sheet, so has limited value.
The viscosity @40C number has me thinking its properties will be more like the Motul than Amsoil.

To further complicate matters, we could speculate on what impact the various viscosities will have on power production or how any of these specs may or may not matter once the oil has been mixed with gasoline.