Hi folks, I had to join this discussion because I have some experience in the lubricants world (having working in R&D and sales for a major lubricants manufacturer). I just want to clear up a few concerns raised here the best I can.
Toyota's WS vs T-IV
- Toyota (see link to Service Bulletin <
http://www.etimago.com/yaris/TSB/TS-TC01...20Fluid ).pdf >) does clearly indicate that THEIR own ATF-WS is NOT compatible with T-IV or Dexron ATF and they recommend only the WS be used in vehicles that call for it. It makes perfect sense that they are not compatible because the additive chemistry is different. This is the same reason you should never add "magic" additives to ATF's to convert one to meet another spec - leave the chemistry work to the reputable ATF manufacturers since they spend enormous amounts of money in engineering and testing of their products.
- It is also true that the viscosity is very different, WS is a fair bit lighter viscosity. The Japanese are big into fuel efficiency and so the WS is designed with a lower viscosity which tends to result in a gain more fuel economy and it is also designing with a different additive cocktail to be a longer life fluid (similar benefits to GM's Dexron VI).
- Why they have not backspec'd the WS for T-IV applications is interesting but I think this is simply to avoid potential confusion especially seeing as the 2 fluids are not compatible - it is easy to see the possibility of dealer filling/top up mistakes.
So to use a "multi-vehicle" ATF (from a reputable company - ideally one that is known to make ATF's) with a slightly higher viscosity, the only real trade off will be fuel efficiency. Fuel Efficiency gains from lower viscosity ENGINE oils is proven with standardized tests but it which is much more difficult to quantify such savings between different viscosities of ATF's as there are so many other variables. If you make a switch to a different product and you experience undesirable "shifting" issues, then you might consider changing it back to the OEM product but I can assure you this is highly uunlikely if you use a reputable brand product. More of a concern is ensuring the old fluid is removed before adding a different one.
Early, Petro-Canada's DuraDrive MV (Multi-Vehicle) product was mentioned and there were concerns of it working in both T-IV and WS applications. Believe me, a major ATF player like Petro-Canada would not put their name on a product unless it was fully tested. Petro-Canada is a major world supplier of many different ATF's - most notably Dexron VI (they co-developed the product with GM and provide factory fill throughout the world)<
http://www.imakenews.com/lng/e_article000384801.cfm?x=b11,0,w >.
Another thing to keep in mind, those oil company's that supply the big automotive OEM's have to be very careful when marketing a "multi-vehicle" product because they are also licensed to make specific OEM labelled products. It is possible that their "multi-vehicle" product meets other spec's but they cannot show it because they risk losing their licensing of "specific" products. The ATF world is becoming very complicated as new designs of transmissions are developed. It is even more complicated because classic universal oils such as the old Dexron III/Mercon have been replaced with OEM specific products. The OEM's make a lot of their money on parts and lubricants are treated as a part so it is in their interest to market and protect their own labeled products.
