[BlueDevil]

May I ask a question, please?
I've read throught this entire thread and I didn't get my mind changed so far (which is to use what factory told me to use). But that aside...

What importance does outside temp have on oil? I know the WINTER part (the number before the "W") is important and why (cold starts etc). What I don't get is the other part where people say things like "0w30 is not good for hot climates". Specifically, where I live we get -10, -15 celsius in winter (sometimes over -20 but that's pretty rare) and we get +35 easily in summer (measured in shade, over the grass on 1m height, as it should be) - so in sun when standing still it will go to +40 no problem.

But what does all that have to do with engine oil? Surely where it flows thge temps are much higher that +40 so if someone says +40 is too hot for 0w30 oil then basically any outside temp is too hot for that oil since it will only get to work temp quicker when starting from +40 rather than starting form +10. Just that.

I belive I've read somewhere that diesel engine's oil working temp is between 100 and 110 dec celsius. So the oil will be working at that temp. The only difference I can see the outside temp makes is that if you start your car on -10 celsius then the oil must be thin enough to lubricate ASAP, and it will take longer for oil to reach 100-110 celsius of operating temp.
If you start the car on outside temp of +30 celsius, then it will be quicker to reach 100-110 celsius working temp - but that's it! The +40 outside or -10 outside won't do anything to oil performance. Anything.

Please correct me if I'm wrong, but the only real problem is to have the oil thin enough in cold weather. Just that. IT will never get over 100-110 outside, and the engine will always try to have the oil at that temp, so I really don't get it.

I mean even if you lived in an area where temps all-year round are from -30 to -10, never over 0 (always celsius), the engine would still be operating the oil at 100-110, just taking longer to get there. And if you were to live in year-round +30 to +60 (always celsius), the engine would reach oil temp of 100-110 quicker, but still would keep it there and try to cool it down if it was to go over that, or warm it up if it was to go under that. But 100-110 range is way higher than environment so it can't possibly have an impact.