I just put a load of 0W-30 into one of my outdoor cars, a 2004 Dodge Intrepid 3.5L for one reason: cold starts. Yesterday, I took advantage of Costco's $10 coupon on cases of 5W-30 and picked up three of those. It got me thinking about just how much different the specs on these two oils are. I guess the answer is, "not much", but I found some unexpected differences.

For example, while 0W has a lower viscosity at 100C (where you'd expect them to be the same), 0W has a higher viscosity at 40C, 62.9 vs. 61.7. Does that trend continue at even lower temperatures? The Viscosity Index of 5W is higher than 0W, 172 vs 166. I thought higher VI's meant better cold starts. Am I mistaken? The Pour Point seems to indicate what one would expect, with 0W lower at -50C vs -42C. Mobil gives an MRV @-40C for 0W but not 5W, so that can't be compared. Not related, but of interest, Mobil specs a seemingly healthy TBN of 9.1 for 0W then doesn't provide the spec for 5W.

I'm sure I could use either oil in any of my vehicles and I like the fact that the 5W is Honda HTO approved when considering it for my turbo Mazda but the real issue for me here is cold starting. What say you oil spec experts about the differences between these two oils? Heck, the Mobil website even gives the 0W a couple of extra check marks on performance. Have UOA's revealed any significant differences? Is it really worth bothering with the AFE's for near 0F temps?

Your right their isn't much difference between the two oils until you get well below freezing.
The one viscosity spec' you haven't considered is HTHS. In fact you can ignore the KV40 and KV100 spec's since we have the VI's of both oils.
The 0W-30 has a slightly lower HTHSV of 3.0cP vs 3.1cP for the 5W-30. That compensates for the 0W-30's somewhat lower VI which would otherwise result in a heavier oil at normal hot operating temp's.

I think the cold starting advantage of the AFE 0W-30 will only rear it's head at temp's well below 0F.

This thread is relevant to my interests. Also interested in comparison to the M1 5W30 EP.

Caterham, thanks for your input. I have seen your many comments on oil specs and respect your knowledge and experience in these matters. In fact, I thought of you when comparing the HTHS specs which are only one tenth apart. But, since my concern was cold starts, I didn't see how the high temp visc played a role in low temp performance and still not quite sure I understand.

And it is really sub-zero (F) cold starts that I'm interested in. 5W has proven to work just fine at 0F.

Again M1 5W-30 's viscosity is not much different from the other two oils with it's HTHSV of 3.0cP and 169 VI.

Personally, of the three oils, in our climate I prefer M1 5W-30 for it's higher HTHSV and VI, but as I said we are splitting hairs.

I also consider CATERHAM the expert and i am trying very hard to go to 0W on all my oils. However, the truth is i presently live in a HOT climate and i wont really EVER see a tempterature anywhere CLOSE to zero degrees (which is below freezing, i can not think of when i will even see 32 degrees) and i could probably be fine with a 5W oil.

Still, the stigma of a 0W oil is great and CATERHAM also talks about how "even at 100 degrees" (which happens most times of the year) it will be lighter at start-up, and that means that i pursue either a 0W or 5W. (Royal Purple 5W-30, Castrol Edge 5W-30, or M1 AFE 0W-30.) In Dallas, Texas. (What if i drive somewhere cold in the winter. Even if i dont... 0W better than 5W right? - Redline 0W-20?)

Agree.

Surely there is a data point that indicates cold start performance? Even though the oils discussed here may be very close, it would be good to have a spec one could compare different brands or even synthetics vs conventionals.

Me neither. How is a specification determined at 150 degC relevant to flow and pumpability at 0 degC? Is there data or evidence demonstrating that HTHS is a better predictor than MRV or CCS, of flow and pumpability at 0 degC, ?

And this is precisely what I'm looking for. Is there a test to identify superior performance at -10F? -20F?

I like your question except for the 0C which of course is only 32F where we all have plenty of first hand experience with successful performance of 5W. Heck, the manuals of my older vehicles call for 10W-30 down to 0F and 5W only when expecting below 0F. I'm looking for an oil that will help that baby start when the battery will barely crank.

CCS specs cover the temp range of -10 to -35 degC
MRV specs cover the temp range of -15 to -40 degC

What is the lowest temp you are expecting this winter?

Isnt 0W better at ANY temperature, CATERHAM?

The main advantage of 0W oils for most application has nothing to do with extreme cold temp' starting performance but rather that generally 0W oils have higher VIs than 5W and heavier oils.
In that sense they are more of a multi-grade oil.

I think where the disconnect can happen is when folks assume that 0W oils are automatically better at cold starts. Obviously, the real answer is "it depends". In looking around at various 0W20 and 5W20 oils, I was stuck by the fact that M1's 0W20 is pretty close to the same viscosity @40C as many 5W20's. "Cold" for me is anything under 50F, so honestly I look at 40C viscosity more than MRV specs.

So, I guess the takeaway is that not all 0W oils are created equal--and don't assume that one particular 0W will offer better cold start protection than a 5W. You have to dig a little deeper than that.