Here's the situation:

A friend used Mobil 5W40 for the very cold weather he experienced in Canada, and because he could not find 0W40.

He came to the US to visit, we went to Walmart and he bought two 1.25 gallon jugs of Mobil 1 0w40.

He is worried about mixing synthetic oils of different viscosities: his diesel uses a little oil and will probably need a quart in another 500 miles.

He's wondering if the mixing of the two viscosities will hurt the oil mix and the engine.

Logically, to me, since they are all the same brand, I cannot see a problem.

However, I would like some info, some real data, not opinions.

The reason I believe as strongly in biodisesel is that I have seen the tests on their extra lubrication capability in tests.

I'd like to find someone who has data or real expertise about this topic.

Unfortunately my buddy Joe in Philly, a retired petroleum engineer, is off some place in Florida and he is not answering his phone.

Have not seen any other posts like that in this forum.

Anyone have references?

Thanks.

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It won't be a problem. From the source:

http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/Harm_Mixing_Different_Mobil_1_Viscosities.aspx

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I believe Shell sells one of the Rotella variants in Ca, it is 0W40.

I've never had an issue mixing oils, when possible I try to avoid it but I've never had anything bad happen.

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When you change your oil, do you drain the oil cooler, lines, and wipe down the engine internally? If not, then you've been mixing oil types all along

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