Hi guys.

Recently I have changed my engine oil from stock 5w30 to Mobil1 new life 0w40. It was recommended by my colleague since Mini engine generates lot of heat, and mostly due to driving habit.

What I realize after the oil replacement, my ECT, engine coolant temp tends to increase quite slowly.
Before it took around 2~3min to heat up to 60 celcius, and with another 2~3 min of smooth driving, it will reach upto 80~90 celcius which seems hot enough for wild driving.

However after the replacement, it takes longer idling time to reach 60, and even with 5min of driving, it barely touches 80celcius. Of course if I drice around more than 15min, it goes up to 105 degrees which is normal for N18 turbo engine.

Can you guys explain what does oil viscosity got to do with coolant temp?

 

It is a fact of reducing friction, that slows the heat up. It also slows the wear on the engine components and thus taking longer to warm up the water jacket.
Full synthetic oil is the only oil to use in a MINI! More of the heat is going out the exhaust, which is also heating the turbo sooner and faster at lower rpm range, due to heat expansion of exhaust gasses.
I hope this helps you see what is going on a little better.