Is one reason that 30 weight oils are thin because...

[Audi Junkie]

...because you are supposed to mix them with 10w-40 when higher viscosity range is desired? Just wondering if this is the intent of oil companies. I just used 50/50 10w-30 and 10w-40 in an oil-burning Hi-Mi Mitsu because I was reluctant to use just 40 weight. Makes some sense to blend, right?

 

[DavoNF]

Good theory, but I don't think so. Most major oil companies have a range of oils to suit all climates and engine types. From a watery thin 5W-20 up to a nice robust 20W-50. If you are burning oil, there is nothing wrong with using a 10W-40, or even a 15W-40. You just have to watch your winter temperatures and adjust your cold visc. accordingly. Dave.