The person you are correcting have not posted in this in thread in about 10 years.

Many people just use the term " oil weight" instead of the viscosity or flow of the oil. It is what it is; not point of trying to educate people on the fine details of motor oil science.

However, I will state that the 2015 RX350 owners manual only allows for the use of 5W-20 engine oil for use in an emergency when 0W-20 is not available and for short term use to be drained at the next oil change. The owners manual makes not mention of 10w-30 as being acceptable to use. So please do not state incorrect information that can damage someone engine. 0W-20 is the proper oil weight(viscosity) to use in the 2010-2015 RX350; not 5w-20 or 10W-30.

 

That section of the manual has bothered me. Cold start? No such problem here in these parts of Texas. I would like to see the manual for a vehicle delivered to hot climates, i.e. Saudi Arabia or something. What does it say? Would love to see it.

 

What bothers me is the ES350 with the same engine in most of the same model years calls for 5w-30.
I think they used 0w-20 to improve their corporate gas mileage average as it gives the RX a slightly improved gas mileage rating.

 

^^ Exactly. More of a CAFE thing than anything else.

 

I disregard what the manual says for our '14, it has been getting 5W-30 for years as does my 08 RX and 02 HL which are specc'd for it. The 2GRs are basically internally identical throughout 05-18, the main documented change being a revised exhaust cam phaser after '09 to address the infamous "death rattle" on startup. The 5W-30 is still more than thin enough below 0 to flow well on cold starts. New 0W-20 oil spec, removal of the all-time 50/50 AWD system, center differential and viscous coupler transfer case of the 07-09 RX, all cost-cutting and MPG decisions to allow Lexus to sell a larger vehicle as emissions regulations became more stringent.

There was a tiny rattle with our '14 on cold starts occasionally on a very cold day, that has gone away with the 5W-30 surprisingly. Maybe more oil pressure from the thicker oil reaching the valvetrain faster? Who knows. I'm sticking with 5W-30 for the extra protection, this car doesn't get driven hard like my '08 but it gets enough WOT highway pulls to make me sleep better at night. MPG difference was not even measurable

 

I stick with 0W-20 in my wife's 2015 RX350 primarily for resale purposes. Our future buyer will see my documentation showing that the vehicle received exactly what its owner's manual specified.

 

Makes sense, and an easy decision for you given your climate. Down here where 115F not unheard of makes the decision a bit more difficult after looking at the operating temp ranges of 0-20. cuts out way below the temps we see all summer in this area. Which is why I would love to see a manual from a hot region. I've seen people claim the spec is different in hot regions, but they did not provide proof.

 

What could have happened as well is that Toyota engineers may have noticed that some of the VVTI gear and timing chain tensioner issues occurring in early model 3.5 engines may have been happening due to start-up wear due to the 5W-30 oil being too thick with poor flow when cold. 0W-20 oil flows very well to get to the many parts that needs it at start-up like timing chain tensioners and camshaft actuators which is a good thing to reduce wear in those parts.