use 10w-30 in place of 5w-30?

[Arkaign]

Dropping an oil grade at operating temp (40 -> 30, or 30 -> 20) reduces fuel consumption by about 2% according to castrol. While it may not be much in real life, it can squeeze you down a bracket with regard to taxes in the euro zone... (where tax is based on g/km and 1-2 g/km can be important).

Changing the ecu setup/oil/gearing is cheaper than other options.

Yeah I kind of get that the drop was for fuel economy, but is it safe enough for my motor? It's not too thin is it? I'd trade 2% fuel economy for a little added protection if there is a notable difference. If everything is good as-is, I'll just stick with the mfg spec 5w-20, but continue supersyn instead of syn-blend. There's literally zero black/ash/residue in my motor as far as I can see, just a nice honey-colored mobil 1 light glaze For contrast, when I take the oil filler cap off of my friend's '08 Jeep Liberty, it has the typical 'dirty' look, even though he has about 10k less miles than me.

 

[HarryLui]

2%

That's 25mpg vs. 24.5mpg.

 

[LTC8K6]

2%

That's 25mpg vs. 24.5mpg.

Paging fleabag...
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[Zenmervolt]

So is the use of synthetic 0W-30 going to be better overall in terms of lubrication and efficiency as the use of 5w-30 dino oil? It sounds like to me you are saying that a straight 30 oil is going to last much longer than a 5 or 10w-30 oil would.. How much worse is a 0w-30 going to be in comparison to a 5w-30? Also is the increase in viscosity modifiers when going from 5w-30 to 0W-30 going to be higher than 5w-20 to 0w-20?

How much longer is a variable amount of time that will depend on any of thousands of different factors. That said, yes, a straight-weight oil will technically protect better than a multiweight oil assuming both are flowing fully. The issue is that a straight-weight oil that is thick enough to function per design specs when the engine is hot will almost never be thin enough when cold to flow properly at start-up. Since the majority of engine wear occurs during a cold start (in the brief period before oil pressure comes fully up), it is important to ensure that the oil is sufficiently thin when cold.

As with most engineering issues for cars, this is a balancing act. Oil has to perform over a wide range of temperatures, especially when seasons change. Since most people won't bother to change their oil based on the seasons (indeed, few enough people bother to change their oil based on the correct mileage), engineers design engines such that multigrade oils offer sufficient protection over a broad range of conditions. If a car specified 5w30 and you lived on the equator, you could probably get by just fine running straight 30 weight all the time since you would never encounter the frigid cold temperatures where the thinner oil would be critical. But someone living in Ohio where they might encounter 95 degree days in August and 0 degree days in December all on the same oil, the 5w30 pays off even though straight 30 weight may allow a person to eek another 500-1000 miles out of an oil change interval.

ZV

 

[Zenmervolt]

ZV, this is kinda off track of the current discussion, but wanted your opinion.

I have the '08 Focus S 2.0 Duratec (16v DOHC i4, 10.0 CR), and the factory oil was Ford Syn-Blend 5w20. After the first oil change I dumped the synblend and have been using Mobil 1 SuperSyn 5w20. Seems great, but should I stick with this or consider other options?

I see nothing wrong with that, but, frankly, I wouldn't bother.

In general, while synthetic is technically better, I just don't see the difference being meaningful in liquid-cooled, naturally-aspirated engines like the one in your Focus. For turbocharged vehicles or air-cooled vehicles I really like synthetic for its superior resistance thermal breakdown, but I just don't see that being a worry in the average street car.

As far as Mobil 1, it's what I use in my own vehicles. Yes, there are oils out there that are technically better, but IMO they are not enough better to justify their price. Mobil 1 occupies what I believe to be the sweet spot on the price/performance graph.

ZV