K3993
Well-Known Member
Where to begin? Lol. What's tough is how anecdotal so much of it all is. On one hand, people claim 5w20 kills engines, on the other, cars last longer now than ever before and 5w20 is very prominent. There's definitely no "one size fits all" option. There's a statement I read that recalled a quote of someone saying that they'd put an engine on a dyno and floor it. Its life was measured in seconds with 5w20, minutes with 5w30, and would run all night with 40w. Considering the temps an engine sees if it's at redline, then sure. Also, if 5w20 blows engines in seconds at redline, I would've just blown my engine tonight. One other big point to consider is how quickly 5w30 shears to 5w20, especially older oil formulations a decade ago. This means that a lot of the high mileage engines, like the 4.6 2v, spent a large portion of its lifetime running 5w20. 5w20 will also shear, especially with fuel dilution, but it doesn't use as many viscosity index improvers so it stays in grade much better and longer. This logic is also why people like the 10w30 so much over at bitog. The smaller the gap in numbers, the less VII. 5w20 and 10w30 also have much lower NOACK values. If someone is in a hot climate and wants to run 5w30, a good argument could be had that 10w30 is the better way to go. Another key point that was brought up is how an oils additive package play a much larger role in antiwear than the oil's viscosity. Another concern is that the oil film, in thin oil, can't protect a bearing from contaminants as well as thicker oil. But, to be honest, the difference in 5w20 and 5w30 is not nearly big enough for this to be a deciding factor. Pennzoil platinum 5w30 has a kv100 of 9.8. Pennzoil platinum 5w20 has a kv100 of 8.9. Also, I'm not sure what bearings Ford uses for the coyote, but bi metal main bearings are designed to prevent debris from becoming embodied in the bearing and easily flushed through. In this case, I'd argue 5w20 is better because it's better flow compliments the bearings design.
There's just so many variables. I used to buy into the argument that clearances haven't changed with the 4.6 (back spec'd to 5w20) and I think I remember reading that the bearing clearances are larger in the 5.0. So 5w30, or greater, would be better. But then I read about how larger aluminum bearings tighten the clearance up more due to greater thermal expansion and, as such, benefit more from thinner oil. So bearing material plays a key role, and not just the amount of clearance that's spec'd.
The next thing is oil pressure. I see a lot of people (myself included, at one point) freak out over low oil pressure. Oil pressure is resistance to flow and is not good. High oil pressure means lower flow and more heat. I think the idea that low oil pressure is bad stems from how low oil pressure would typically be a result of some sort of failure, like worn out bearings (more clearance, less resistance, lower oil pressure). Low oil pressure also seems to be an issue with high load and low rpm applications, but I haven't learned enough to go too much into this. So thinner oil is ideal on high revving engines. However, greater engine speeds also creates more heat, so this is why heat management is crucial if you want to run thinner oil. "Oh but the boss 302 calls for 5w50!" Go away. I hate this argument, and this is coming from someone who was in the thicker is better camp. 5w50 is spec'd because the car is assumed to be seeing a lot of track time with increased engine speeds and heat that go well beyond what 5w20 can handle. It's also not financially practical to dump the oil after every track session. 5w50 is fine for occasional street driving and frequent track use in the same way that 5w20 is fine for occasional spirited driving with frequent street driving. 5w30 may still be the better option, especially if the new GF-6 testing gives us much more shear resistant oils. But there's no definitive proof one way or the other.
I'm no engineer, and I'm learning as I go. So take what you will out of all of that. However, my personal opinion is that thinner oils are definitely the way forward. They're just more efficient overall. Remember, not too long ago 5w30 was viewed the same way as 5w20 is now (won't protect well, only for CAFE, etc). Although I will admit that the 0w16, or whatever it is, is pushing it a bit. I think we're at least a decade away from being able to safely use oil that thin.
Thank you for the additional thoughts on this subject, always appreciated.Where to begin? Lol. What's tough is how anecdotal so much of it all is. On one hand, people claim 5w20 kills engines, on the other, cars last longer now than ever before and 5w20 is very prominent. There's definitely no "one size fits all" option. There's a statement I read that recalled a quote of someone saying that they'd put an engine on a dyno and floor it. Its life was measured in seconds with 5w20, minutes with 5w30, and would run all night with 40w. Considering the temps an engine sees if it's at redline, then sure. Also, if 5w20 blows engines in seconds at redline, I would've just blown my engine tonight
There's just so many variables. I used to buy into the argument that clearances haven't changed with the 4.6 (back spec'd to 5w20) and I think I remember reading that the bearing clearances are larger in the 5.0. So 5w30, or greater, would be better. But then I read about how larger aluminum bearings tighten the clearance up more due to greater thermal expansion and, as such, benefit more from thinner oil. So bearing material plays a key role, and not just the amount of clearance that's spec'd.
The next thing is oil pressure. I see a lot of people (myself included, at one point) freak out over low oil pressure. Oil pressure is resistance to flow and is not good. High oil pressure means lower flow and more heat. I think the idea that low oil pressure is bad stems from how low oil pressure would typically be a result of some sort of failure, like worn out bearings (more clearance, less resistance, lower oil pressure). Low oil pressure also seems to be an issue with high load and low rpm applications, but I haven't learned enough to go too much into this. So thinner oil is ideal on high revving engines. However, greater engine speeds also creates more heat, so this is why heat management is crucial if you want to run thinner oil. "Oh but the boss 302 calls for 5w50!" Go away. I hate this argument, and this is coming from someone who was in the thicker is better camp. 5w50 is spec'd because the car is assumed to be seeing a lot of track time with increased engine speeds and heat that go well beyond what 5w20 can handle. It's also not financially practical to dump the oil after every track session. 5w50 is fine for occasional street driving and frequent track use in the same way that 5w20 is fine for occasional spirited driving with frequent street driving. 5w30 may still be the better option, especially if the new GF-6 testing gives us much more shear resistant oils. But there's no definitive proof one way or the other.
I'm no engineer, and I'm learning as I go. So take what you will out of all of that. However, my personal opinion is that thinner oils are definitely the way forward. They're just more efficient overall. Remember, not too long ago 5w30 was viewed the same way as 5w20 is now (won't protect well, only for CAFE, etc). Although I will admit that the 0w16, or whatever it is, is pushing it a bit. I think we're at least a decade away from being able to safely use oil that thin.
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