One of the reasons to go for a 0/5 W20 over a 5/10 W30 is for the oil to pump more quickly around the engine at non operating temps.
Using synpower as an example, at 40c the cST for 5w20 is 48 vs at 100c being 8.65. For 5w30 it is 59 and 10.5 respectively.
At lower temps the cST increases exponentially. I found a graphing program that said at 0c 5w20 would be about 400 cST and 5w30 would be 475cST
So my questions are this;
1) Clearly the cST's are huge at non operating temperatures compared to at operating temperatures. This means oil will not flow as quickly by a huge order of magnitude at non operating temperatures. In that respect, discussions about 5w20 vs 5w30 vs 15w50 seem irrelevant as far as the second number is concerned. Why do I say this? Well a lot of the concerns I have read seems to be that thicker oil won't flow around the engine freely enough, that gaps are smaller and the oil might not get everywhere.
Well if the cST for 5w20 is in the hundreds when cold and that is tolerable for the warranty period let alone hundreds of thousands of miles, why would single digit cST differences between 5w20 and 5w30 at operating temperatures make any difference? In the case of a cold start at 0c, a cST of 400 is still deemed to protect the engine, so why would going from 8.65 to 10.5 at 100c cause any issues whatsoever?
2) If a 0c 5w20 Cst is 400 and a 0c 5w30 Cst is 475, is the 5w20 that much better than the 5w30? The reason I ask is as follows. They are both labelled as 5w so presumably when the temperature gets lower, the 5w30 closes the gap a little. Also, as the temperature drops, the cST's go up even more. So the oils, rated for temperatures below 0c, will flow even more slowly below 0c then at 0c. Such cST's for the 5w20 will be deemed acceptable, thus cST's for the 5w30 at temperatures ever so slightly higher than the 5w20 will also be acceptable. Ie if the 5w20 was ok flowing that slow, then the 5w30 would be also.
So really my conclusions are as follows - which I would love to have corrected(!)
1) That unless you are reaching the lower ranges of allowable temperatures for your 5w20/30, there is no real cold start benefit from using 5w20 vs 5w30. The flow rate at 0c is relatively unimpeded compared to lower than 0c.
2) That the engine is not impacted by a 30, 40 or even 50 weight oil compared to a 20 weight oil at operating temperature because at non operating temps these same oils flow at rates many orders of magnitude slower and are deemed to protect.
3) That the really important judgement that needs to be made is whether the 20 weight oil is too thin to prevent metal to metal wear. Clearly as you approach zero cST, the difference between 10 and 8 is quite big.
Thoughts & Criticisms?
Using synpower as an example, at 40c the cST for 5w20 is 48 vs at 100c being 8.65. For 5w30 it is 59 and 10.5 respectively.
At lower temps the cST increases exponentially. I found a graphing program that said at 0c 5w20 would be about 400 cST and 5w30 would be 475cST
So my questions are this;
1) Clearly the cST's are huge at non operating temperatures compared to at operating temperatures. This means oil will not flow as quickly by a huge order of magnitude at non operating temperatures. In that respect, discussions about 5w20 vs 5w30 vs 15w50 seem irrelevant as far as the second number is concerned. Why do I say this? Well a lot of the concerns I have read seems to be that thicker oil won't flow around the engine freely enough, that gaps are smaller and the oil might not get everywhere.
Well if the cST for 5w20 is in the hundreds when cold and that is tolerable for the warranty period let alone hundreds of thousands of miles, why would single digit cST differences between 5w20 and 5w30 at operating temperatures make any difference? In the case of a cold start at 0c, a cST of 400 is still deemed to protect the engine, so why would going from 8.65 to 10.5 at 100c cause any issues whatsoever?
2) If a 0c 5w20 Cst is 400 and a 0c 5w30 Cst is 475, is the 5w20 that much better than the 5w30? The reason I ask is as follows. They are both labelled as 5w so presumably when the temperature gets lower, the 5w30 closes the gap a little. Also, as the temperature drops, the cST's go up even more. So the oils, rated for temperatures below 0c, will flow even more slowly below 0c then at 0c. Such cST's for the 5w20 will be deemed acceptable, thus cST's for the 5w30 at temperatures ever so slightly higher than the 5w20 will also be acceptable. Ie if the 5w20 was ok flowing that slow, then the 5w30 would be also.
So really my conclusions are as follows - which I would love to have corrected(!)
1) That unless you are reaching the lower ranges of allowable temperatures for your 5w20/30, there is no real cold start benefit from using 5w20 vs 5w30. The flow rate at 0c is relatively unimpeded compared to lower than 0c.
2) That the engine is not impacted by a 30, 40 or even 50 weight oil compared to a 20 weight oil at operating temperature because at non operating temps these same oils flow at rates many orders of magnitude slower and are deemed to protect.
3) That the really important judgement that needs to be made is whether the 20 weight oil is too thin to prevent metal to metal wear. Clearly as you approach zero cST, the difference between 10 and 8 is quite big.
Thoughts & Criticisms?
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