Syn/non Syn oil mix

[EXPSD]

I have a Duramax with 3200 miles on it and would like to start using Rotella T. I also have 6 gallons of 15W 40 reg. Rotella that I purchased for my last Diesel that I do not want to waste. Can I mix 50/50 until the Reg Rotella is used up and than go 100% with Syn. I asked on the Rotella forum and did not get an answer.

[hickcox]

I don't see why you would want to mix the two types, why not just use the regular Rotella to break in the engine thoroughly first?

Or better yet,...Take the six gallons you have laying around, back to the store and exchange it for six gallons of the Rotella T syn. and pay the difference. The auto parts stores around me are usually quite accommodating, call around first.

Can't hurt to try?

[EXPSD]

Here is the answer from the people that know: The Rotella Web site expert(great site).

The two oils are generally compatible, and can be used with each other when topping off. However, mixing ROTELLA T Synthetic, or any synthetic based oil, with ROTELLA T SAE 15W-40 is not a recommended practice. Each oil has been carefully formulated so that its additives provide optimum performance in its particular base oil. Mixing two oils with different additives and different base oils creates a third oil with unproven performance, which may pose unknown risks. I’d use up the ROTELLA T SAE 15W-40 and then switch to ROTELLA T Synthetic.