Quote:
Originally Posted by teoman
I recall reading on bobistheoilguy.com quite the opposite. (no personal experience).
The explanation was that if you have thinner oil, it flows more removing more heat.
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Again depends on operating conditions. On the track, the oil can get so hot the bypass doesn't activate at 7000rpm and 50wt oil thins down to what 20wt would be at normal temperatures. As long as the bypass doesn't activate, you have the same oil flow (since the viscosity is a little higher, you'd expect a slightly different distribution of oil flow between different parts of the engine).
On the street your oil is never getting hot like that unless you're driving way too fast, so it makes sense to go one grade thinner (if your engine can live at 270+F on 50wt oil, it'll be fine at 220F on 40 or even 30).