Any benifits to using 40 over 20?

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I have a 2009 Mazda 6 3.7L with 25k on it. The manual states use 5-20 but if its not available use xW-30 or xW-40. I can find plenty of 5w-20 but AA has M1 0w-40 and a filter for $29. I've heard a lot of good things about this weight.
 
The 5w20 might bring you slightly better fuel economy (if you even notice it), possible a bit more horsepower because the oil isn't as heavy, and possibly better cold flow properties.

If they say that a 30 or 40wt is fine then I would use whatever you can find that is cheap and meets your need.

0w40 is a very good Mobil oil.
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Being of a Chrysler background. (Dad was a mechanic for 35+ years and worked for them) I would tell you that it's nothing more than to promote CAFE standards from that company for Jeeps.

The 3.7 in my experience likes a thicker oil. I would go with a 30wt if you are using it for daily driving or in the colder weather and a 40 if off-roading and tearing it up/towing.

M1 0w40 is a very good oil that would be suitable year round though... Although I think those engines do best on Pennzoil if you like that brand.
 
I agree with stevo 5w20 first choice for mileage or the 0w40 for a outstanding oil,pick up both and run them then chose.
 
We dump 5w20 in everything that cap calls 5w20 at work. I don't see any reason not to do that. I would stick with PP5w20 that your using (if you like it).
 
Sorry I saw the Rubicon in your name and goofed... Then in your Mazda I would use the 5w20 in the winter and 5w30 in summer.

Pennzoil for both cases... 0w40 is a tad to thick for my liking in that engine.

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on my part... Sorry.
 
Warranty OCI
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I was thinking the same about 40 being to think and not needed. I like the idea of 20 winter/30 summer.
 
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