I respectfully disagree ,in anything but very cold temps like 0-20deg f 10w base oil in a 10-30 oil pumps up just fine/fast enough and isn't an issue at all.
The motor oil temps charts i have read from oil mfg's rate 10-30 safe down to 0deg f but to be safe i would not run it below 20 deg f.
The reason why i prefer /suggest 10w 30 over 5w-30 for street perf BBC/SBC motors is because the base stock 5w oil in a 5w-30 oil can shear/reduced in viscosity before the 10w base oil does in 10w-30 oil not to mention the additonal chemical additives in 5w-30 to get to 30wt when hot.
I have read oil tests done over the yrs that showed just that point so i feel going with 10w base oil in a 10-30 multi viscosity oil you get a little better protection against thermal/viscosity breakdown vs 5-30.
Another point is that they need to add more chemical additive to get 5w base oil to 30wt oil when oil gets up to proper operation temp then going from 10w base oil to 30wt oil when hot making the 10-30 a little more durable/stable then 5w-30 for hi perf use.
Are hi perf motors going to blow up because they are running 5-30 oil,not likely. But it still doesnt take away from the fact the 10-30 oil did a little better then 5-30 did with all else being = in the oil tests i had rvu'd . Again,that was due to the 10-30 multi visc oil having a 2x higher visc base oil (10w vs 5w) along with it also requiring less chemical additives in the oil to get it from 10w to 30wt when hot vs getting 5w oil up to 30wt oil when hot.
When both thoses oils are at proper operating temp the 5w-30 with lower visc 5w base oil & more additives to hit 30w sheared/broke down a little faster viscosity wise . It wasn't a day & night difference but non the less the 10-30 did better overall then 5-30 did & thats the point.
And the 10w base oil in a 10-30 on cold start isn't an issue at all in the temps we run these cars/motors in .
Starting/running a motor in a daily driver in 0-10deg f temps would be a different story and in that case i woiuld prefer 5w-30 over 10w-30 but the fact is most of us run these limited use /non daily driver cars in temps above 40-50 deg & 10w's not an issue there at all for cold startup.
And thats not even getting into the fact if somoe's running a semi blend or full syn oil that they flow better convetional oil does in cooler temps.
Just my $.02 on that.
Scott, I don’t disagree with the technical details you reference. But those hair splitting differences are negligible and don’t stack up to much of anything in running engines in the real world.
And for the record, I had in mind, premium quality full synthetic oil, when I wrote my response, though I neglected to specify that. I barely even consider dino oil anymore, and I sort of think of it like bias ply tires, a thing of the past.
The range between the cold viscosity rating number and the operating temp viscosity rating number of 5W30 is of course 25, while that number for 10W30 is of course 20. The difference between the two ranges is only 5. Not a huge difference, but that gives you cause for concern, because of base stocks and added chemicals.
Well, how about the range between the old favorites 10W40 or 20W50? Their range is 30, which is 5 more than the range for 5W30. Yet I doubt you ever had concern about them, since they have been used with great success for decades. So, with your line of thinking, 5W30’s range should be more desirable than theirs. To make it a little more clear, here is a list for easy comparison:
20W50 = 30 spread
10W40 = 30 spread
5W30 = 25 spread
10W30 = 20 spread
That puts 5W30’s spread right in between your preferred 10W30 and the old 10W40 and 20W50 favorites. I guess the 5W30 can’t be too bad, huh?
Lots of people, myself included, have run premium quality full synthetic 5W30’s in some stout running engines for years without any issue at all. Personally, I run it in all my stuff, including a 600hp Supercharged small block, an 800hp BBC, as well as a 430hp GTO, and in regular daily drivers. No problem so far……...in any of them. Bottom line, 5W30 works just fine in a wide range of applications, with no down side. Though with that said, I’d only use or recommend premium quality full synthetics.
Sacrificing cold flow ability for the misguided hope of getting infinitesimally better protection between 5W30 and 10W30 is a good way to shoot yourself in the foot, in my opinion.
Its commonly understood that around 90% of all engine wear occurs at cold start up, during the brief time before oil gets to all the engine’s internals. 5W30 will get there quicker than 10W30, no matter what the ambient temp is outside. And getting oil to all your engine’s components as quickly as possible, is a difference that offers real value.