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I have a 2007 Mazda 3 GX which I just took in for an oil change @ Canadian Tire. On the receipt they wrote down the filled it up with 5w30 oil. I was looking through my manual today and under the maintenance section I noticed it said to use 5w40 oil. I don't know that much about cars and I was wondering if I should worry about this or if everything is okay? When I took my car in they never asked me what type of oil so I assumed they would have some sort of a reference lookup to inform them based on type of car.

Thanks
 

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I'm pretty sure the manual will call for 5W20, not 5W40, unless (maybe) your car is a grey market diesel imported from some market where Mazda sells the 3 with the 1.6L diesel. This is unlikely and seems like something you would quite aware of if it were the case. ;)

As for what oil the manufacturer calls for vs what CTC mechanics will put in, years of behind the counter experience tells me whatever is in the bulk tank is the correct grade.

Anyhoo, 5W30 won't do any harm, it just doesn't get quite as thin as 5W20 when the oil is up to operating temp. In theory this could result in a 1-2% increase in fuel consumption. Personally, I feel this unlikely possibility is a worthwhile trade for increased engine protection and have switched to 5W30 myself.
 

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[quote author=bustednutz link=topic=136201.msg2943425#msg2943425 date=1234913281]
I also use 5w30 as well.  Every other country specs it for the 3 except the US.  Its a C.A.F.E. thing.
[/quote]

What does that mean ("C.A.F.E. thing")?
 

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C.A.F.E. = Corporate Average Fuel Efficiency.

A government/EPA mandated thing which requires manufacturers to meet a minimum average fuel mileage number for their entire line of vehicles.
 

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So does that apply to the 2.0 as well? I thought the 2.3 recommend 5W-30, but the 2.0 recommended 5W-20? Edit: I mean in every other country. So, say in Japan, what would be the spec for the 2.0?
 

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Does A Higher Grade (5w20 -> 5w30) Increase Performance And Decrease Fuel Economy? Or Is It The Other Way Around. I've Heard Too Many Things To Believe Anything ><
 

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The lower viscosity of the 5W20 at operating temp supposedly reduces viscous drag in the engine. In theory you could maybe, possibly get slightly better fuel economy and make slightly more power by using 5W20 instead of 5W30. In practice I seriously doubt the slight difference in viscous drag would make any measurable change in either fuel consumption of power in low rpm, low output engines like ours in the real world. If we were turning 10,000+ rpm and squeezing out 200-300 hp/L then maybe there would be a measurable difference between 5W20 and 5W30 but at 6,500 rpm and ~150 hp the difference is probably much less than 1%.

If you want some hard numbers from an actual oil company, Petro-Canada provides a handy PDF file which compares viscosity and such for their line of synthetic motor oils. It is easy to see how the 5W20 has apparently quite a bit lower viscosity at high temp than the 5W30. I'm sure other oil companies can provide similar data which will show much the same general comparison for their products.
 
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