Pauly001

I wonder if not only emissions dictates the lighter oil but the engine design with that water cooled oil cooler in the “v” works better to dissipate the heat along with the hot “v” design. Possibly the flow rate through the cooler then the turbo is better with a thinner oil at operating temps.

Nick Tremblay

Great questions.

EDIT: I initially made some typo errors that may have compromised adequate understanding. Sorry for that. See corrected text below.

1- This one can be confusing, it's not obvious to explain it through a forum. A manufacturer may required a specific grade, the reality if that the engine is designed to deal with a broad range of different oil viscosities, because the temperature varies a lot. The take away here: engine can deal with a broad range of viscosities without being hurt. At -20 Cesius start up, a 0W-20 oil will have a viscosity too great to be measured in centistokes, while it will have a viscosity between 9.3 and 12.4 centistokes at 100 Cesius, typical normal operating temp. So using a viscosity different than the one specified, say a 0W-30 instead of a 0W-20, won't have direct adverse effect, because if one fear that a 0W-30 will be too thick for the engine, keep in mind that using the recommended 0W-20 will be way thicker at -20 Cesius start up than the 'so feared' 0W-30 at normal operating temperature. If the thick 0W20 at -20 celcius didn't break the engine at start up, then 0W30 won't hurt anything at 100 celcius.

2- Again, not obvious to cover this over a forum. I can't share any specific document here because what I know about this is based on the sum of my education, work experience, reading (Lubes'N Greases, Lubrication Machinery) and several phone discussions with contacts I have in the oil industry. So it is up to you to believe or not. Being critical of what we read on web forums is totally ok and you're welcome to challenge. So don't take my word for it and I invite you to check for yourself (read, call oil company technical services). However, I won't share any specific document, because it does not boil down to a single piece of document.

3- I don't know much on the B-cycle engine differences. The Budack cycle refers to a different version of the Miller cycle (related to the intake valve timing), the intake ports have a different shape (on the 2.0 TSI 137 kW) and a variable displacement oil pump. If somebody here know more about it, please feel free to share. In a nushell, this specific intake valve timing improve fuel/air mix inside combustion chamber, which improve burn efficiency, hence the fuel economy. Opting to a lighter oil to be ran in B-cycle engine makes senses, with fuel economy in mind, manufacturer wants to takes all the necessary steps to optimize: not only a 0W-20 VW 508 is lighter than previous VW 50X specifications, but it comes with a maximum limit of High temp High shear viscosity, meaning that the engine can benefit from an even lower parasitic load from oil internal friction in engine high shear areas, such piston rings, camshafts, etc. All this benefit better fuel economy. The different oil pump has been likely designed around that 0W20 VW 508 spec, but again, remind the point #1: this pump can handle very thick, cold 0W20 lubricant at startup, so I wouldn't be concerned for that pump with a warm thin 0W30. What I don't know is what controls the pump flow variation: RPM ? load (viscosity) ? That, I don't know.

Nick Tremblay

Question: 0W-20 is the same flow or thickness(viscosity) when cold as 0W-30, hence the “0”.

Not necessarily the very same viscosity.A 0W refer to a maximum Cranking and Pumping viscosity at -35 and -40 Celcius respectively (see SAE J300). So 2 different 0W-xx oils MAY have different viscosities at low temperature, because the 0W label is granted to a lubricant that meets the criteria, think in in viscosity range (or maximum allowable), not a specific measured viscosity.

Question: If the thickness was different at -20c SAE probably would not certify the rating scale across all oil brands as a standard.. would you agree?

I do not agree. Two 0W lubes may have different viscosity at -20C and be labeled 0W because both meet the criterias. Again, see first question and answer. the 0W label is granted to a lubricant that meets the criterias. According SAE J300, a lubricant can be labeled as 0W if its maximum Cranking viscosity does not exceed 6200 cP at -35C and if its maximum Pumping viscosity does not exceed 60000 cP at -40C.

Question: When hot the 0W-30 is thicker than the 0W-20.

Only at a given temperature ! A 0W-30 at -20C will be a lot thicker than a 0W-30 at 100C. See this graph and see for yourself. https://www.quora.com/What-is-a-tran...ansmission-oil

bhvrdr

Ill be honest nick im a little more confused now

1. Your statement was that a 0w20 is thicker than a 0w30 at cold temps. I took that to mean both oils at the same cold temps nick. Certainly youre not comparing a 0w20 at cold temp to a 0w30 at warm temp? You do realize such a comparison should not be made for considering the proper viscosity across all operating ranges?

2. Here i specifically asked you what the difference is beteeen the vw504 spec and vw508 as far as actual requirements to meet certification and it appears you do not have an answer. How can you speak about certifications that you have not seen the full requirements for? While many engines operate well on many different viscoosities depending on climatecand operating conditions we Certainly also know there are engines out there that do require a very specific viscosity and certfication of oil.

3. You dont know much about b cycle differences nor obviously that the two engines (2.9 and 3.0) have identical oil pumps but very specific electromechanical controls nor how thise cintrols operate. Dont you think knowing what these differences are would be important before suggesting audi simply required vw508 for fuel economy and to please put on a non approved oil viscosity? Here you also again bring up cold pumping vs hot which i am confused why you would do that.

Nick Tremblay

Well .I'm sorry I could not answer your questions to your satisfaction. I tried my best but it appears that words on a forum won’t achieve the clarifying level that we look for. Next step would be for you and me to meet in front of a white board....the cofee is on me !

Pauly001

Last try.
All factors the same in comparing the two oils at 100C is the 0W-30 thicker..?
I would assume the 0W there is a range of viscosity that allows it to be rated a 0W. Where I struggle is the 0W-20 called thicker at cold temps.

Nick Tremblay

Yes of course, at a given temperature, say 100C, a 0w-30 is expected to be thicker than a 0w-20.

I’ll try this way: those numbers are arbitrary, are unit less , its a scale system, they are no centistokes or centipoises, they are grades that refer to how the viscosity behaves with temperature.

Take aways:

• Numbers in 0W-20, 5W-40 etc. do not represent direct viscosity readings, they are an arbitrary unit less numbers, they are part of scale system to get an idea how the oil viscosity behaves with temperature. Refer to SAE J300.
• For any grade, say 10W30, it’s viscosity varies all the time with temperature change. There is no such thing as a fixed viscosity for lubricating oils. The grade (scale system SAE J300) gives an idea how the viscosity behaves with temperature.
• When you start a cold soaked engine at -20C, yes you can expect that a 0W-30 is thinner than a 5w-30 at the same temperature, however, this 0w-30 is nonetheless very thick at -20C. It’s viscosity will decrease as the engine warms up.
• For those who fear that a 0W-30 will harm a EA888 gen3b budack cycle engine specced with 0W-20 grade...think this: the real measured viscosity oil at -20C of any 0W-xx oil would be, say 5000 cst. Yes, the engine will handle this viscosity at startup. Once at operating temperature of 100C, a 0W-20 grade will have a measured viscosity between 5.6 and 9.2 cst, while 0w-30 grade will have a measured viscosity between 9.3 and 12.4 cst You will agree that even with the 0W-30 grade, the viscosity at 100C (about 10 cst) will always be way thinner than any 0W-xx grade at cold start up temperature (say 5000 cst). However, the b-cycle engine is designed to handle such thick viscosity at cold startup without breaking. So you can expect the same engine to handle any 10 cst oil at normal operating temp ( yes a 0w-30) without breaking as well.

To explain more than that....we will need a video conference with board and pen (we can arrange that

Ps: I appreciate those questions, challenges and intellectual curiosity. Keep going.

bhvrdr

Nick we understand oils behave differently with respect to fluidity at different temperatures we just cannot figure out why in the world you would compare a 0w20 cold viscosity to a 0w30 hot viscosity.

Saying the engine is great for a 0w30 because a 0w20 is thicker at cold start than a 0w30 is at hot is crazy. A 0w20 at 40c is twice as thick as a 10w60 oil at 100c... of course... but that doesnt mean you should run a 10w60 in a car that specs 0w20.

I think we were confused because no one would expect you to be comparing cold viscosity of one oil to hot on another. Try running the car to redline daily on an oil that is not at operating temp yet and see how long the engine lasts.

Nick Tremblay

Question: why in the world you would compare a 0w20 cold viscosity to a 0w30 hot viscosity

Answer: To put things in perspective about the marginal risk to use a slightly different viscosity grade than the one recommended. Comparing cold and hot viscosity illustrates how broad is the viscosity range an engine can handle.

Comment: Saying the engine is great for a 0w30 because a 0w20 is thicker at cold start than a 0w30 is at hot is crazy. A 0w20 at 40c is twice as thick as a 10w60 oil at 100c... of course... but that doesnt mean you should run a 10w60 in a car that specs 0w20. I think we were confused because no one would expect you to be comparing cold viscosity of one oil to hot on another

Reaction: I agree with that. It is not necessarily 'great' and it doesn't mean you 'should' use an higher viscosity grade than recommended. However, I would be careful by qualifing a forum perspective as crazy. Those are words on a screen and it's sometime challenging to expose properly one's line of thinking. Comparing hot and cold viscosities is certainly a different, non-conventional educationnal approach about lubricant, but it remains valid IMO to put certain aspects in perspective. I'm sorry it didn't work as intended this time.

Comment: Try running the car to redline daily on an oil that is not at operating temp yet and see how long the engine lasts.

Reaction: I agree, and to be honest, I was expecting this one to come up. Knowing that my engine can handle a 6000 cP lubricant at idle with no load doesn't mean it can handle it at hign RPM with loads. Granted. Hence this analogy can certainly illustrates that an engine can handle without harm a 2 cSt difference at normal operating temp, which is often the difference between an xW-20 and a xW-30, which was the main purpose of this example.

Nick Tremblay

https://www.lubrizoladditives360.com/vw5080050900/

https://www.lubrizoladditives360.com/vw5040050700/

Here is a part of the « proof » requested earlier on this forum about the VW 508 spec if the only driver is in fact fuel economy and if it includes other specific performance requirements.

See links above. The answer is pretty clear comparing VW 508 and VW 504 requirements from Lubrizol: the only difference is a lower HTHS...for fuel economy, all others requirements are identical. A quick search will reveal the the point in using lower HTHS is reducing fluid motion internal friction.

Take away: any VW 504 approved lubricants satisfies performance requirements by VW 508 specced engine....except HTHS viscosity, which is for fuel economy.

The only disagreement remains about the viscosity grade (VW 504 = xW-30 vs VW 508 = xW-20), but we already trade a lot of comments and FAQ to allow one to make his/her head around this.