oesman
Well-Known Member
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- Feb 18, 2016
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- Houston, TX
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- Dmitry
- Vehicle(s)
- 2016 Mustang GT PP
I'm running Motul 300V Chrono 10w40 which is their car formula. I posted some thoughts/results here:
https://www.mustang6g.com/forums/showthread.php?t=92145
So while you're 100% right that the bearing clearances do not change, the thickness of the oil absolutely changes with forced induction. That 5w20 can act more like water than oil if you get it hot enough. The downside of going thicker is that when you're not at your hot operating temperatures the engine may get less protection.
If you assume that a normal daily driver using 5w20 has about 190F oil temperature puttering around a highway; You can see on the attached image that a 15w40 should be of a similar viscosity at 250F under heavy load. So the question is what is your actual operating oil temperature and how thick will your oil be at that temperature and will that meet your needs for lubricating your engine? Adjust as necessary.
https://www.mustang6g.com/forums/showthread.php?t=92145
This is true assuming temperatures are within spec. Multi-grade oils (i.e. 5w20, 5w30, etc...) are designed to protect daily driven cars across a range of temperature from cold start in Alaska to warm run in Houston. However, when you push the car hard, with a power adder and especially on a race track that 5w20 is now very fluid having lost all it's viscosity and protection. This is why we used to run thin oils in the winter and thick oils in the summer, before these multi-grade oils became used in everything.The way I always have looked at it, the weight of oil is determined by the bearing clearances. Forced induction does not change the bearing clearances, and knowing what I know now about how tight they are, I would not go with a thicker oil.
So while you're 100% right that the bearing clearances do not change, the thickness of the oil absolutely changes with forced induction. That 5w20 can act more like water than oil if you get it hot enough. The downside of going thicker is that when you're not at your hot operating temperatures the engine may get less protection.
If you assume that a normal daily driver using 5w20 has about 190F oil temperature puttering around a highway; You can see on the attached image that a 15w40 should be of a similar viscosity at 250F under heavy load. So the question is what is your actual operating oil temperature and how thick will your oil be at that temperature and will that meet your needs for lubricating your engine? Adjust as necessary.
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