Will 0w-30 be different than 5w-30 in a warm climate?

That is a good question. Supposedly, Mobil 1 0W-30 does offer a slight fuel economy improvement over M1 5W-30. Note that I said "slight" improvement. If you're hoping for 5-10 MPG, look elsewhere

M1 0W-30 and 5W-30 are both rated the same by Mobil, they both claim to exceed API/ILSAC SM/GF-4. They both meet the tougher European spec ACEA A1/B1.

Hot viscosity, there are two different SAE approved ways of measuring. The first is a kinematic test at +100 C oil temp, which is under ASTM D445. Any oil claiming to be a "30" such as straight 30, 10W-30, 5W-30, or 0W-30, *must* test 9.3-12.5 cSt (CentiStokes). No exceptions

The second test is a dynamic one under ASTM D4683. This is a high temperature high shear test, run at +150 C oil temp, and 10^6 shears/sec. Any oil claiming to be a "30" *must* have a minimum viscosity of 2.9 mPa s (Milli Pascals per sec). No exceptions

Mobil 1 5W-30 is rated by Mobil as having a kinematic viscosity of 11.3 cSt, and a dynamic viscosity of 3.09 mPa s. Flash point is +230 C

Mobil 1 0W-30 is rated by Mobil as having a kinematic viscosity of 11 cSt, and a dynamic viscosity of 2.99 mPa s. Flash point is +228 C

THose test results are a virtually identical rating. If one oil tested say 12.3 vs 11 cSt, that is a difference. Or if one oil had a HTHS of 3.6 mPa and the other had 2.9

A lot of conventional oils are designed to shear on purpose, to enhance fuel economy. Mobil 1 oils are designed not to shear at all, providing better engine protection.

Also keep in mind that both oils are specifically approved by GM for use in the high performance Corvette

So use whatever oil you feel is appropriate. Around here, the 0W-40, 0W-20, 0W-30, 5W-30 of Mobil 1 are the same exact price. If the dealer wants to be a real tool about it, have him state in writing that 0W-30 can't be used

 

Whoa, that is a *big* increase! Like I said, around here *all* the regular Mobil 1 grades (0W-20, 0W-30, 0W-40, 5W-20, 5W-30, 10W-30) are the same exact price, around $8.99 a litre

I used to run Mobil 1 5W-30 and 0W-30 in my Prius before switching over to 0W-20. When the temps were above -18 C, there was no difference in mpg I could detect. I only noticed a *slight* improvement - maybe 3 MPG - running the 0W-20 at -30 C, especially -40 C

You'll be fine with the 5W-30. Unless your dealer wants to be a tool and puts in writing "no synthetic allowed, will void warranty" or some such nonsense. If they do, demand a sample of their wonderful no-name bulk lube oil, send it off for testing, and show them the results

That was how I got Toyota Canada to STFU

 

When I bought M1 0W30 in the 5 qt jugs at Walmart, it was the same price as the M1 5W30. It is harder to find though; it seems to only be carried at a few Walmart stores.

I think either one is fine. I have been using the 0W30 for the last two OCIs.

 

Keeping your warranty hassle-free and use a 5w-30 would be my choice.

5w-30 and 0w-30 are both 30 weights at operating temperature. The difference you are looking for is not in the 5w or the 0w.

The difference you seek is the 30 weight viscosity at operating temperature. There are 30w's that are lower viscosity and those with a higher viscosity at op temp. The lowest two viscosity oils at temp that I've been able to find are Havoline Deposit Shield 5w-30 and Castrol Syntec 5w-30. Havoline is a standard oil and the Syntec is a synthetic.

Either are good oils. I use the Havoline. The Syntec is too pricey. Modern oils are good enough that it really isn't much of an issue with 5k mile change intervals.

 

Bottom line is for a warm-ish climate the 0W-30 is not terrible useful over a 5W-30. But if the oil were the same price from a quality synthetic maker (e.g Mobil) I would choose the 0W-30 over the 5W-30 every time.

At startup temps the 0W is thinner than the 5W, even fractionally - which can lead to less wear, negligible though it might be. Another consideration is that from some makers the 0W-30 is a "flagship" product and is designed for the longer change interval. For examls the Amsoil SSO 0W-30 is their flagship oil designed for at least a 17,500 miles in severe service and 35,000 (!) in regular service (or one year in both cases). One can save injecting much waste oil with that many miles between changes.

I choose Amsoil 0W-20 here in New Jersey as it's rated for almost as many miles as the SSO, and the 20 weight oil has been shown to give very good results in the Prius.

As far as warranty goes, the Magnuson-Moss Warranty act covers us so that a maker cannot invalidate a warranty simply because one used other than 5W-30 or 5,000 miles. They must show the oil caused the issue to get out of warranty work. And one will have the oil maker on your side for the deep pockets against the auto company (bad for oil business if they can't sell oil as they want to).

Rumple