Question about mixing different oils
 

Ok, so I'm currently using Rotella 15W40 oil in my car, but it's a quart short and I need to top it off. Is it ok to top it off with 5W40 (since it's getting cold here)? Or would that mess everything up since the latter is thinner than the former? Would it be better to just do an oil change if I want to use the thinner oil?

Answer
 

Esentially it will drop the viscosity of your oil, not a bad thing in cold weather.

IMO you should be running a 0W40 or 5W40 all year.

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yup. works fine. no problems. as long as BOTH oils are diesel rated, you'll be fine.

when is the next oil change due?