If all oil is too thick when cold...

Shannow covered most of it. I'd also add cost and specifications. Some will follow the specifications to the letter (as in it it's 5w-30, they'll only use that, even if 0w-30 AFE is acceptable). Others want to use conventional, so they'll use the 5w-30 ahead of the 0w-30.
 
I agree with the original premise...in most cases, assuming oil cost is the same, there's really no good reason to not use a 0W grade. Yes, it, too, is still much heavier when it's not at operating temperature. Even Toyota's 0W-20 is about FOUR times as heavy at 104 deg F than it is at operating temperature (somewhere around 32 cSt vs. somewhere around 8 cSt). So even with the hottest cold start you can imagine, and even with a 0W-20 with a really good VI, the thickening as it cools (even at over 100 deg F) is significant. Why put unnecessary load on your starter and electrical system?

Outside of special engine requirements, the biggest issue with most users is either cost (0W- grades usually cost more than conventional oil) or warranty (some owner's manuals list only 5W- or 10W- grades).

If you don't care about warranty, or aren't under warranty, and if you're going to buy synthetic anyway, then I see zero reason to not use a 0W- grade. (The only reason I have 5W- grades in my cars now is because they're "free" $5-off-$5 purchases at O'Reilly from last year.)
 
Quote:
If you don't care about warranty
The Factory Warranty is a non issue in the US....Period. An OEM cannot void a factory warranty because you use a viscosity not listed in your manual...period!

A failure must occur that can be attributed to the lubricant used. If the OEM can't prove that, they must provide warranty coverage for the failed component....Period.

It's time to put these warranty concerns to rest. If the oil didn't cause a failure, the OEM factory warranty can't be voided. The burden of proof is on the OEM in the US. The magnuson moss warranty act of 1975 provides this protection for any car bought in the US.

However, be advised that this may not true for "so-called" extended warranties, which are, in many cases, insurance policies or service contracts. check the mice type. You might be surprised with what you have. Unless it is a extended OEM warranty, the Magnuson Moss Warranty Act may not apply. Insurance policies and service contracts, that provide repairs may not cover you if you violate any provisions of your manual (including NOT having your vehicle serviced at an OEM dealership). Know what you really have and service your vehicle accordingly. In may cases, an extended "so Called" warranty is an expensive trap, not the piece of mind, it was sold as.

Needless to say, I do not buy extended 3rd party warranties for this reason.
 
Originally Posted By: spasm3
How much real difference in startup flow is there from a 5w 20 to a 0w 20 in say 20f?


None, Nada, Zip, Zilch.

They are both at least 35F above the temperature at which any of their respective pumpability issues are possibly going to come to the fore...the oil pump will shift exactly the same quantity of either per revolution of the engine.

20F, a 10W and 15W are still completely in the safe range 20W, 25W are going to be fine typically.
 
Originally Posted By: BrianC
An OEM cannot void a factory warranty because you use a viscosity not listed in your manual...period! A failure must occur that can be attributed to the lubricant used. If the OEM can't prove that, they must provide warranty coverage for the failed component....Period


Many modern vehicles have a ambient temp/viscosity chart in the owner's handbook while other's specify a heavier oil based on the climate or usage. Here are 3 manuals I can put my hands on right now:

2014 Porsche Panamera Owner's Manual Page 257: "0W-40 for winter - 5W-50 for high temperatures"

2014 Corvette Ower's Manual Section 10-15: "For competitive driving, use Mobil 1 15W-50"

2015 Maserati GT Owner's Manual Page 207: "Fully synthetic 5W-40 all climatic ranges"
 
Back in the day, every OM had a temp/visc chart and every OM allowed for the use of a range of grades.
For more than a decade, alternative grade recommendations have been rare.
An exception can be found with Subarus. The current flat four has only one recommended grade, but for the earlier timing belt engines, a range of grades and even API specs was allowed.
The OM of our '09 Forester states that an API SM 5W-30 is prefered, but then goes on to allow the use of just about any thicker grade you can think of, including a 40 or a 20W-50 as long as the oil is at least an API SL.
A 10W-30 or 10W-40 is allowed for down to about -4F.
This is all OT and not responsive to the OP's question.
At the coldest ambients most of us typically see, the difference between a 5W-XX and a 0W-XX will be tiny. At really cold temperatures, some type of external heating might be of more value than a 0W-XX oil, as another poster noted above.
Someone also noted that a 0W-XX grade must be synthetic.
Not so. Honda markets a syn blend 0W-20 and there is also a Maxlife syn blend 0W-20. If any manufacturer actually recommended a 0W-30, we'd probably see it offered in a syn blend as well and there'd be a lot more readily available oils in the grade than just the API SL Syntec 0W-30 or the API SN M1 AFE.
 
Originally Posted By: BrianC
A failure must occur that can be attributed to the lubricant used. If the OEM can't prove that, they must provide warranty coverage for the failed component....Period.


This is correct, and nothing in my post contradicts this. Some people are worried about going outside the recommendations because of this potential. Some are not. It's a non-issue for many, but it's still relevant to note.
 
Originally Posted By: spasm3
How much real difference in startup flow is there from a 5w 20 to a 0w 20 in say 20f?


Flow? None. Viscosity? Potentially a lot.
 
A straight 30 is the wrong oil then winter temps are below freezing. Just to get a base for proper w selection of oil viscosity.
 
There are oil applications that have little to do with driving down the road at legal velocities.

But for these applications, a different (set of) numbers are generally what one looks for; Such as:
HTHS for tack related oil applications. It is almost impossible to find a HTHS number over 4.0 with
a 0W-xx as the leading viscosity oil-weight-grade indicator.
 
Originally Posted By: spasm3
How much real difference in startup flow is there from a 5w 20 to a 0w 20 in say 20f?

It depends on the 0W-20 but M1 0W-20 for example is about 20% lighter and a light 0W-20 like TGMO about 50% lighter at that temperature.
The lower the viscosity of the oil the higher an engine can be rev'd cold before oil flow begins to be restricted.
At that temperature, initially on idle the heavier 5W-20 I suspect should have the oil's pumpability largely unrestricted. The reduced flow would begin at some elevated rpm above idle. Consequently the lighter the oil, the higher it can be rev'd without oil flow being restricted.

When you start an engine at that temperature and then drive off your oil flow will be greater with the lighter oil even at low road speeds.
Even on a cold start at room temperature with the very light TGMO 0W-20, if you rev' an engine any higher than about 2,500 rpm oil flow will begin to be restricted until some heat starts to thin it out. The lower the temperature the lower the engine rpm that this will happen.

Since most cars aren't equipped with an oil pressure gauge so that you can tell at what rpm the oil flow is being restricted during warm-up, one can generally conclude that more oil is being pumped with a 0W-20 than a 5W-20.
 
Caterham;
I took him off of your hand for a few days to give you a rest.

You know what his response is going to be.

"Your and your oil pump, please explain how a positive displacement.......ect"
 
What's the point of oil grades like 5w-30 or 10w-30 or 15w-40? Why not just use 0w-30/0w-20/0w-40 when possible? I've read and searched but could never find a definitive answer
In Washington State I don't think you'll find a case where all three of the grade of oil listed won't work just fine. Especially if you car get parked inside.
 
5w30 ACEA A5 is less viscous than 0w30 ACEA C3.

10 vs 12 cst on 100 Celsius, and 55 vs 65 cst on 40 Celsius.

SAE rating is missleading.
 
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