Start Up Flow Clarified ?

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My question is : Do all 5W synthetic oils (5W20 , 5W30 , 5W40) flow the same rate in a cold engine that has sat over night ? In other words a 5W20 should not flow any faster upon starting up an engine than a 5W40 synthetic oil would correct ?
 
Why are you asking about flow? The winter rating does not measure flow.As long as the oil can be pumped it will flow.
Cranking and pumpability is what the winter rating measures.

And it is entirely temperature dependent. Unless you are at very low temperatures where the winter rating is important then a 40-grade is always going to be thicker than a 20-grade or a 30-grade.
 
My question is : Do all 5W synthetic oils (5W20 , 5W30 , 5W40) flow the same rate in a cold engine that has sat over night ? In other words a 5W20 should not flow any faster upon starting up an engine than a 5W40 synthetic oil would correct ?
For the most part, flow rate depends on the oil pumps gallons per minute, however, if the oil is extremely thick, some of it cold flow out of the pressure relief valve, that being said, a 5w40 will definitely be thicker at say 0 degrees than a 5w20.
 
Flow? The oils ability to flow from the sump to the oil pump. after the oil pump the oil is pressurized .
 
Generally speaking, you are correct. The two 5w-xx oils will flow the same at startup in the engine.


Now, let the 'Actually..." and "What about..." replies from everyone begin!
Generally speaking, you are incorrect. See graph below. 0W40 has almost twice the viscosity at freezing as 0W20.

Screen Shot 2021-09-27 at 1.52.37 PM.jpg
 
Generally speaking, you are incorrect. See graph below. 0W40 has almost twice the viscosity at freezing as 0W20.
Generally speaking, you are incorrect. See graph below. 0W40 has almost twice the viscosity at freezing as 0W20.

View attachment 72609
The W rating is about pumpability / flow what ever we want to refer to it as,, not viscosity . There are specific SAE test procedures for the W ratings.
 
*OP here - perhaps "flow" was not the correct word to use - more specifically I am curious about start up wear protection differences (if any) between 5W20 , 5W30 synthetic oils : Since they are both a 5W rating do they both circulate to critical engine parts at or near the same rate when both the oil and the engine are cold ? Here I have either read where a member will switch from 5W30 to 5W20 in the Winter or substitute a couple of quarts of 5W30 for 5W20 in cooler month operation . If both oils are 5W is that necessary to increase start up wear protection ?
 
*OP here - perhaps "flow" was not the correct word to use - more specifically I am curious about start up wear protection differences (if any) between 5W20 , 5W30 synthetic oils : Since they are both a 5W rating do they both circulate to critical engine parts at or near the same rate when both the oil and the engine are cold ? Here I have either read where a member will switch from 5W30 to 5W20 in the Winter or substitute a couple of quarts of 5W30 for 5W20 in cooler month operation . If both oils are 5W is that necessary to increase start up wear protection ?
Startup wear is not due to oil viscosity, it's due to increased clearances between cold, shrunken parts, the lack of heat needed to activate the additives, moisture, and fuel dilution washing the cylinder walls.
 
Generally speaking, you are incorrect. See graph below. 0W40 has almost twice the viscosity at freezing as 0W20.

View attachment 72609

Well then Chapter 2 of this website’s Motor Oil University needs a correction, as it definitely leads the reader to believe 0w-xx oils behave similarly in colder conditions.

I’m specifically referring to the halfway mark on this page: https://bobistheoilguy.com/motor-oil-102/

Where it says:
“Similarly, you could compare 0W16, 0W20, 0W30 or 0W40 as all having similar cold temperature performance, but with different ranges in high temperature performance.”
 
Well then Chapter 2 of this website’s Motor Oil University needs a correction, as it definitely leads the reader to believe 0w-xx oils behave similarly in colder conditions.

I’m specifically referring to the halfway mark on this page: https://bobistheoilguy.com/motor-oil-102/

Where it says:
“Similarly, you could compare 0W16, 0W20, 0W30 or 0W40 as all having similar cold temperature performance, but with different ranges in high temperature performance.”
Yes , this is the basis of my question : There should be no difference in cold temperature performance between 5W20 and 5W30 at say 20 degrees F. yes or no ?
 
Yes , this is the basis of my question : There should be no difference in cold temperature performance between 5W20 and 5W30 at say 20 degrees F. yes or no ?
I have asked a similar question below but never really got a straight answer.
My conclusion to this question is; even though both 5w-20 and 5w-30 (for simplicity assume the same brand) can both be pumped at the same low temperature since they are both 5w. At at any given temperature the 5W-30 will have a higher Kinematic Viscosity.
 
I have asked a similar question below but never really got a straight answer.
My conclusion to this question is; even though both 5w-20 and 5w-30 (for simplicity assume the same brand) can both be pumped at the same low temperature since they are both 5w. At at any given temperature the 5W-30 will have a higher Kinematic Viscosity.
*So the guy who says : "For winter I'll substitute a couple of quarts of 5W20 in place of my normal 5 quarts of 5W30 for better cold temperature protection" ... Is wasting his time ?
 
Well then Chapter 2 of this website’s Motor Oil University needs a correction, as it definitely leads the reader to believe 0w-xx oils behave similarly in colder conditions.

I’m specifically referring to the halfway mark on this page: https://bobistheoilguy.com/motor-oil-102/

Where it says:
“Similarly, you could compare 0W16, 0W20, 0W30 or 0W40 as all having similar cold temperature performance, but with different ranges in high temperature performance.”
Also from the same page (paragraph one):

"If the operating temperature is 212F and the recommended viscosity is 10cSt then OIL A which can be made to be 40 cSt at 104F(40C) is going to be better than OIL B that is 100cSt at 104F (40C). They will both will still be too thick at start up and during the warm up period but OIL A will flow better and waste less energy. When these oils are pumped, they may move at the same rate, but the thicker oil will require more energy to make it move."
 
Also from the same page (paragraph one):

"If the operating temperature is 212F and the recommended viscosity is 10cSt then OIL A which can be made to be 40 cSt at 104F(40C) is going to be better than OIL B that is 100cSt at 104F (40C). They will both will still be too thick at start up and during the warm up period but OIL A will flow better and waste less energy. When these oils are pumped, they may move at the same rate, but the thicker oil will require more energy to make it move."

Yes, heavier oil takes more energy to pump. Is it significant? No. But that's part of the reason for that thinner oils are being spec'd for CAFE, those tiny incremental gains in efficiency/economy.
 
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