Originally Posted By: Shannow
It's funny, but your monograde 10W20 would warm up quicker than an uber VI 0W20, with more viscous drag in that warmup regime.
Looking at Toyota and Honda stuff, it's the warm-up range that they are really targetting, short tripping.
Do you think that you could make a mono 20 with an HTHS around the 2.6 mark instead of 2.8 to 3 ?
Shannow, I don't have my old box of tricks to answer such questions but I would have guessed you could get 10W20 to at least 2.6 HTHS.
Yes, I know that a lot of OEMs target the 'very low temperature end' of fuel economy and it's here where 0W20's will shine the most and 10W20 won't. However, if I look at my own driving habits, I might typically start the car when it's 10-15°C ambient (so expect the sump temp to be a few degrees higher). The water temperature light goes off after maybe 90 seconds so I know the engine's warming up quickly. As often as not, after 5 - 10 minutes I'm on the motorway and I'm going to guess the oil's equilibrated with the water temp in another 10 minutes because there's so little oil to heat up in my tiny sump.
So say there are three phases from 10°C to 100°C; 10->40, 40->70 & 70->100. A 0W20 will do way better than a 10W20 in that first phase but here's the thing... for a lot of cars, this will be a very short transient phase because this is when the rate of oil heat-up is at it's highest. For phase 2, the relative FE advantage of the 0W20 will still be there but much diminished. For phase 3, I doubt if you will see any FE advantage. If you drive say for one hour or more, the 10W20 will be giving you much the same overall FE as a 0W20.
And here's the big thing...the 10W20 will require cheaper, heavier base oils, less (no??) VII, a lot less DI and it will have a low Noack. For me, these are significant pluses that more than compensate for that small differential in overall FE. At the end of the day, oil FE is a financial benefit from which you have to subtract the differential cost of the oil. If you widen the financial calculation, my instinct is that the numbers will favour a cheap 10W20 over an expensive 0W20.
Finally, remember that engine oil warms up relatively quickly but cools down relatively slowly. If I drive an hour to see my grandson for a few hours, the oil will still be warm when I set off on the return journey. So phase 1 (the one that favours 0W20) may be very short lived on the way back. Given that most human driving involves going somewhere and coming back later, this is probably significant.
PS - I should add that I have a 0W20 in my Suzuki and I'm pleased with it but a 10W20 might be just as good and better in other respects.