Different specs for esentially the same engine?

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Burning question I have.... I am not 100% sure that thinner is better, nor do I think thicker is better. I am in the middle. My question is this. My Mazda3 is NA, and specs either 5w30 or 5w20. The turbo version of the car specs 5w30, which makes sense due to higher temps, etc. Many use Rotella 5w40 in the car with good results. So my question is: Besides the turbo, the cars are very similar. So, what prevents one from using a heavy 30/ thin 40 in the NA version of the car? Any terrible consequences? Just curious, as I am looking to keep one oil in my garage to fit all sizes. Thanks.
 
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I think my 07 Focus has about the same engine as your Mazda, and I use M1 5-30 EP in it with great success. Did one UOA at 9200 miles and showed many miles left in it. Any good 5-30 synt. will work well for you winter and summer.
 
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 Originally Posted By: BTLew81
Burning question I have.... I am not 100% sure that thinner is better, nor do I think thicker is better. I am in the middle. My question is this. My Mazda3 is NA, and specs either 5w30 or 5w20. The turbo version of the car specs 5w30, which makes sense due to higher temps, etc. Many use Rotella 5w40 in the car with good results. So my question is: Besides the turbo, the cars are very similar. So, what prevents one from using a heavy 30/ thin 40 in the NA version of the car? Any terrible consequences? Just curious, as I am looking to keep one oil in my garage to fit all sizes. Thanks.
I'm sure there aren't any terrible consequences. I would run in in a hot climate especially if you drive it hard without any worries.
 
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Funny you bring this up as we have been discussing oil viscosity as it relates to not only protection, but performance with our Australian cousins. Same motor ( GM LS1) and the Aussies use 20-50 religiously with great success....and GM recommends 5-30 here. Go figure. Bottom line is run it ( the 40 weight) with absolutely no worry of doing any harm to your motor man.
 
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 Originally Posted By: BTLew81
Burning question I have.... I am not 100% sure that thinner is better, nor do I think thicker is better. I am in the middle. My question is this. My Mazda3 is NA, and specs either 5w30 or 5w20. The turbo version of the car specs 5w30, which makes sense due to higher temps, etc. Many use Rotella 5w40 in the car with good results. So my question is: Besides the turbo, the cars are very similar. So, what prevents one from using a heavy 30/ thin 40 in the NA version of the car? Any terrible consequences?
Only consequence is slightly lower mpg, see what that car runs in another country, it maybe 5w-30 or 10w-30. I just put 5w-30 Mobil 1 EP in a Civic specked for 5w-20, I found no noticeable loss in mpg.
 
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BTLew81

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I know that they spec 40 in other countries. I know for a fact the couple of OCI's I ran with GC, which is more like a 40, it ran much quieter. In general, these engines have noisy cam followers, and the thicker oil really quieted it. I'm thinking Rotella 5w40.
 
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 Originally Posted By: GrampsintheSand
Funny you bring this up as we have been discussing oil viscosity as it relates to not only protection, but performance with our Australian cousins. Same motor ( GM LS1) and the Aussies use 20-50 religiously with great success....and GM recommends 5-30 here. Go figure. Bottom line is run it ( the 40 weight) with absolutely no worry of doing any harm to your motor man.
don't hang your hat on australians using 20w-50. many folks don't understand lubrication and the benefits a thinner oil could bring.
 
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