mnmike59
Well-Known Member
- Joined
- Apr 5, 2016
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- 2 hours South of BIR
- Vehicle(s)
- 2016 Mustang GT PP
This makes sense to me Norm, Well said. Now I wonder if a heavier viscosity has an equal ability, better or worse to remove heat?I've just read through this entire thread, and the thing that stands out in my mind is that nobody has even attempted to correlate viscosity index to absolute viscosity. They aren't the same thing, as there's a high dependence on temperature.
MC in 5W20 may well be 'adequate' for relatively low oil temperatures and "normal street driving" that presumably implies easier driving than Mustang GT's are prone to seeing. 'Adequate' means that the oil will measure acceptably close to what the absolute viscosity of 20-weight oil is at whatever that DD temperature is, which is apparently acceptable to Ford even from the warranty point of view.
When you take that same car out on the track for 20 minutes or more, your oil will run considerably warmer, and will be thinner in absolute terms as a result. But the engine still needs at least the same amount of protection as it did at the DD temperature with 20-weight, meaning that you do need to look at oils with bigger hot numbers.
There will be a temperature above that DD oil temperature where the absolute viscosity of (for example) 30-weight will be equal to 20-weight at the DD temperature. If that happens to fall about where your track temperatures are, then you'd need to step up at least to 5W30. My own suggestion would be to make the step to full-synthetic at the same time.
Some engineer, ex-Ford with knowledge of this topic beyond what I think is present here, first name Scott (IIRC), wouldn't run 5W20 at least in semi-syn in any modular motor. Period.
Norm
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