5w40 synthetic in ALL of my engines. That includes my diesel truck, my 3kw generator, my SUVs and Passenger cars (which say to use 5w20 but in other countries go up to 15w40 in hot climate areas), my lawnmower, my snowthrower, and any other 4 stroke engine I come across. Never had an issue with the thicker viscosity nor cam phasers which are reliant on oil flow. I'm not a believer in 5w20 oil because it is only there to promote fuel economy at the expense of engine longevity. My 2013 Santa Fe lists 5w20 or 5w30 oil in warmer temps but for other parts of the world, its 5w30 all the way up to 15w40 in their manual. Why is that? Is the 100 deg F in the middle east hotter than the 100 deg F heat in Arizona? Not buying it.
HDEO 5w40 oil has more antiwear additives, suspend insoluble better to prevent them wearing engine components and better shear stability and ability to handle high temperatures.
I've even run it in a Jeep 5.7L engine that strictly recommends 5w20 oil or their camshaft phase system would not supposely work. Think about it, when an engine and oil are cold, their oil vicsocity is higher than a 5w40 oil at 100 deg C temperature.
Pleaes don't preach to me about tighter engine tolerances. That may be been true in the 50-70s when engines were fairly loose and quality was poor which a lot of manufacturing variations. Piston to cylidner, piston end ring gaps, connecting rod to crankshaft bearing clearances haven't gotten tighter in the past 20 years or so. Lighter oils is nothing more than acheiving better fuel economy to satisfy the EPA.
BTW, did you know that new modern oils to meet ACEA A5/B5 specs in 5w30 oil weights must show a 2.5% improvement in fuel economy over a 15w40 oil?
Wonder why semi's still use mostly 15w40 oil today? Perhaps it is what allows them to go over a million miles and more before needing new pistons and rings.
I will put my money where my mouth is. I bought a new car 2 weeks ago. I put 1110 miles on it in 5 days with the factory 5w20 fill. Since it is cold here right now, I switched to 0w40 and will use it in winter months and use 5w40 in summer months. It is a Hyundai Elantra and I'll let you know over the course of the next 10 years how it is doing. So far getting 42-44 mpg on the highway at 70mph with cruise set on the 0w40 oil and I'm very happy with this figure.
