Mixing dino oils?

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Is it bad to mix? Mixing different viscosities of the same stuff is OK, right? How about mixing different brands of the same and/or different viscosities? The best of both worlds or a waste of time? Ex. Mixing 3 qts of Formula Shell 10w40 with 3 qts of Pennzoil 5W30? Mixing 3 quarts QS with 3 quarts Pennzoil 5W30? Or 1 quart Mobil 1 5W30 with 5 quarts QS or Pennzoil 5w30? [ April 25, 2004, 10:28 PM: Message edited by: FL-400S ]
 

TC

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I don't have the link available, but not long ago I read a Chevron website that stated that mixing various weights of the same brand (keep in mind that Castrol GTX and Castrol Syntec, for example, are two DIFFERENT brands) is perfectly fine. But mixing different brands is frowned upon since you may not end up with an optimal, or even effective, net additive package, in spite of the fact that motor oils are meant to be compatible. Putting a bunch of leftover oils in an old beater engine, such as one bottle of Castrol, one bottle of Pennzoil, one bottle of Valvoline, etc.) is something I can understand, although I'd hesitate to do even that. Otherwise, why would anyone assume "I know better than Chevron and Pennzoil...I'm gonna be a junior chemist and mix oils." What's the point? And what is gained?
 
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quote:
Originally posted by FL-400S: Is it bad to mix? Mixing different viscosities of the same stuff is OK, right? How about mixing different brands of the same and/or different viscosities? The best of both worlds or a waste of time?
Probably not good to make a regular practice of it, but at times it may be necessary. Say you are on a long trip and forgot to pack an extra quart of your normal oil. You get gas and check the oil finding you are a quart low and the gas station does not carry your brand. What to do. Get a quart of decent oil that they do carry in the same grade you use and pour it in. I could see boosting your oil with a quart of synthetic for the winter starts. Probably best to stay within the same oil company and check with them. I guess I am a bit reckless, though, using up various oils that I bought here and there I once had a witches brew in my wifes van: Valvoline Durablend 5w30, Valvoline Maxlife 5w30, Royal Purple 10w40, Citgo 10w40, and Rislone Engine Treatment. Her van now has all Valvoline Maxlife 10w30. My pickup had 5w30 in it when I installed an oil pressure gauge. Seeing the pressure was below spec, I wanted to try a 10w40. But the oil had just been changed. So I pulled two quarts out (6 qt capacity) and replaced them with 20w50, which gave me roughly a 10w40. I liked the resulting oil pressure and so now am running 10w40. BTW, the two qts I pulled out went into the wife's van as noted above.
 
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