at one time motorists were advised to not use 5w-50 for example because this wide range of viscosities requires more vi than 5w-20 and vi was rumored to lead to premature oil breakdown, etc. is this still the case or have the oil guys whipped this problem? ford said use 5w-30 when I bought my truck and now 5w-20 is recommended. which is best?
viscosity improvers
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Don't stress yourself there Hub,,,just run what the owners-manual says to run,imho.
The technology of viscosity modifiers has improved over the years and the viscometric shear that was the main concern can be solved. That being said, not all oil manufacturers use the higher end polymers in their formulas for many reasons. So an SAE viscosity rating with a larger spread does not automatically mean an oil is less shear stable than one with a smaller spread, but it can be true.
Different polymers are more mechanically stable than others. So if a stable polymer is used it won't matter what the viscosity rating is because it will retain its viscosity better than a less stable polymer. What viscosity is best is likely the one that the OEM recommends. They have an vested interest in your vehicle not breaking down prematurely (at least until the warranty runs out).
Different polymers are more mechanically stable than others. So if a stable polymer is used it won't matter what the viscosity rating is because it will retain its viscosity better than a less stable polymer. What viscosity is best is likely the one that the OEM recommends. They have an vested interest in your vehicle not breaking down prematurely (at least until the warranty runs out).
If it were my vehicle, I'd use 5-30
A little extra film strength provides an extra level of protection
Steve
A little extra film strength provides an extra level of protection
Steve
In the hot South Carolina, given the age of your vehicle, 10W-30 is probably even better -- less VII and probably higher HTHSV (the latter very likely so if higher 100 C viscosity). Higher viscosity will lower your oil consumption.
Oil has reportedly improved over the years, BUT, I would use 5w-30 if your manual calls for it. But consider this:
5w-30 may be ok if you putt around in a northern climate
OR
just put in a semi-synthetic and call it a day....Synthetics tend to make the viscosity spread without problems.
5w-30 may be ok if you putt around in a northern climate
OR
just put in a semi-synthetic and call it a day....Synthetics tend to make the viscosity spread without problems.
It was hinted by another poster, but they're viscosity index improvers. They don't necessarily improve viscosity (since a particular number isn't necessarily better or worse), but the viscosity index - being how the oil resists thinning. Everything is just formulated to achieve a desired viscosity at operating temperature.
I'd think that a lot of newer "conventional" oils are using different basestocks than years ago and require less VII. These base oils are supposed to have a higher inherent viscosity index. Stuff like Group II and Group III, or even PAO and esters.
I thought that one reason for going to 5W-20 over 5W-30 was that often the VII would break down such that it ended up being close to a 5W-20 oil anyways, and it worked just fine. On top of that, I think a typical 5W-20 is actually thinner at non-winter temps than a 5W-30. The 5W number measures pumping at some subzero temperature. For a typical summer cold start, the Mobil 1 0W-40 I've got in my car is already thicker than the "conventional" 5W-20 in my wife's car.
I'd think that a lot of newer "conventional" oils are using different basestocks than years ago and require less VII. These base oils are supposed to have a higher inherent viscosity index. Stuff like Group II and Group III, or even PAO and esters.
I thought that one reason for going to 5W-20 over 5W-30 was that often the VII would break down such that it ended up being close to a 5W-20 oil anyways, and it worked just fine. On top of that, I think a typical 5W-20 is actually thinner at non-winter temps than a 5W-30. The 5W number measures pumping at some subzero temperature. For a typical summer cold start, the Mobil 1 0W-40 I've got in my car is already thicker than the "conventional" 5W-20 in my wife's car.
Originally Posted By: y_p_w
I thought that one reason for going to 5W-20 over 5W-30 was that often the VII would break down such that it ended up being close to a 5W-20 oil anyways, and it worked just fine.
No that was a BITOG myth that gained legs by being repeated by proponents with an agenda so often.
First question asked in questioning was "what does a 20 shear down to ?"
Answers to that were that they "stayed in grade"...which was disingenuous as the industry already knew that 20 was far too wide until the 2013 update, after which they started dropping out of grade.
Also, 30s start with an HTHS of at least 2.9, 20s 2.6...oils typically lose percentage wise half the drop of the KV100..."sheared" 5W30 is a vastly different beast, but it suited their agendas to try to make it lore...
I thought that one reason for going to 5W-20 over 5W-30 was that often the VII would break down such that it ended up being close to a 5W-20 oil anyways, and it worked just fine.
No that was a BITOG myth that gained legs by being repeated by proponents with an agenda so often.
First question asked in questioning was "what does a 20 shear down to ?"
Answers to that were that they "stayed in grade"...which was disingenuous as the industry already knew that 20 was far too wide until the 2013 update, after which they started dropping out of grade.
Also, 30s start with an HTHS of at least 2.9, 20s 2.6...oils typically lose percentage wise half the drop of the KV100..."sheared" 5W30 is a vastly different beast, but it suited their agendas to try to make it lore...
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