Mixing Oils
 

I sold my 84 diesel, but still have enough 15W40 Rotella T left for one more oil change, and I want to use it for the next oil change on my 89 300SE, which had been getting dino oils every 4k miles. However, I have been adding a quart of oil between oil changes, so I am wondering if it is ok to add different brand different viscosity oils?

Let me "mix" in another question, is there a shelf life for motor oils?

Others may gasp, but I don't see the big deal in mixing oils. It's certainly not as big a deal as mixing greases, which is a no-no. You seem to be conscientious about oil maintenance which is what really matters. The issues of weights, mixing, brands, etc., have only secondary importance.

I once looked for something published on oil shelf life and found it on the Mobil oil web site. Mobil assures 10 years shelf life for unopened bottles, but I can't remember if it's for the synthetic or dino oil.

It's okay to mix modern motor oils - API service category, viscosities, mineral or synthetic base.

Duke