quote:The API Engine Oil Classification Chart only gives "w" weights up through 25w. The weights represent a grade category with a range of viscosity (see chart). A 30 weight ranges 9.3 to 12.5 cSt at 100C. A 40 weight ranges 12.5 to 16.3. If you mix 30 weight with 40 weight you will either get a thick 30 weight or a thin 40 weight, but it will be somewhere in between. You can calculate it on this Calculator (just put dummy values in for the 40C to make it work). The 100C viscosities are available at the manufacturer's web site ( Valvoline Product Data for example). Or there is a pocket calculator formula. In any event the mixed viscosity is a bit below the arthmetic mean of the two viscosities. Edit: Here is the equation behind the fancy blending calculator Gary and I posted: Log Vs = (n log V1 + (100-n) log V2) / 100 where Vs = viscosity sought n = percent by weight of the first component of the blend having a viscosity of V1 V2 = viscosity of the second component of the blend. You can easily expand the equation to handle three oils in the mix. Happy mixing: Oh yeah, if you want to explore oil mixing, check this thread out. [ April 27, 2005, 03:24 PM: Message edited by: TallPaul ]
Originally posted by GreeCguy: Good afternoon fellow oilers: Quick question - if I mix a quart of 30W with a quart of 40W, will I then have two quarts of "35W"? Likewise, a 20W mixed with 40W would that make two quarts of 30W? Thanks in advance.
quote:Oh great! Now two women hate me for playing with oil. Yeah, once you mix it up it seems you can't stand to let it just sit in the jug. Gotta use it. I usually start my mixing a week or two before the anticipated oil change.
Originally posted by GreeCguy: My wife is going to hate you!