I just had my oil changed. But I was reading that the 0w-20 gets better gas mileage than a 10w-30 would get in the same car. Please engineers explain to me how this could be true.

 

Why wouldn't it not be true. For the record I'm not an engineer but a simple car enthusiast.
0W or 10W is not really relevant to our conversation as the W stands for winter and it's just the indicator of the flow of oil at low temperature.

What is important is the number that comes after it which is relevant at operating temperature. The 20 weight oil is lighter then the 30 weight oil therefore there is far less viscosity fluid friction which allows the motor spin with less resistance. It's akin to moving your arm in molasses vs water which is an extreme example but in reality the difference is not that great between the two oils.
Because there is less resistance the car will achieve better gas millage as well as power but that might come at a cost of reliability so that is why Toyota formulates their oils with an abundance of anti wear additives.

 

While this is true in theory, is there any data demonstrating the improved mileage with the lower viscosity oil?

 

I'm sure there is but I never seen any of these publications. I have heard though the internets long ago that some race teams use lighter viscosity oils in their cars to qualify as it gives them an edge. The auto industry publishes some pretty intensive studies kind of like peer review.
These studies are then disseminated across the industry.

 

"This" is a pronoun used to indicate a person, thing, idea, state, event, time, remark, etc., as present, near, just mentioned or pointed out, supposed to be understood, or by way of emphasis. Plural form is These.

titling the thread appropriately so the correct people who have expertise in the area know to read it would help you. All the info you need, is in this thread:

http://www.bobistheoilguy.com/motor-oil-108/

 

LOL. Wow.....

 

I think the original thread topic was "explain These to me" - however, the correction comes off just a bit pompous.

 

That was my point. LOL. Just a BIT....

 

What do people put in these cars? I know it calls for 5w20 or 0w20, but I've been running the 5w20, I just don't feel comfortable putting something as thin as 0w20 in an engine. The stuff flows like water when you pour it. I imagine I might get .1 mpg more out of it, but I worry about engine protection.

 

The W number has nothing to do with the thickness of the oil. The W stands for winter not weight. An oils final viscosity is at temperature.
As an example a 0W-40 is thicker then a 10W-30.

It's not just about fuel savings as much as matching the cars engines viscosity with the tolerances for the kind of service the car will see.

 

There was no correction, I was just bein a smart ***. He said Explain "THIS" to me. So I put the definition of THIS on here. But then followed with a link to answer his question

 

Ah-so - that's the thing with electronic forms of communication - can't put a wink and a nudge in a thread response.

One thing I will note about oil viscosity - I've had two different Lexus service writers from two different dealers both caution me to use only 0W-20 oil. Has something to do with the problems related to the knock sensors being overly sensitive and causing low-power conditions immediately after an oil change.

However, given that I live in Houston, TX, where we care very little about the cold-weather aspect of oils I find the caution a bit over-zealous. My first oil change was with 5W-20. I'm coming up on my second in a few hundred miles and I'll be using 0W-20 - no need to tempt fate, right?

 

And they're right. I have used 5W20 for two oil changes now and had the hesitation issue occur. After I added some Rislone Engine Treatment the issue disappeared. In doing research and with the help of DevH, it seems that the VVT-I system and other components really want the 0W20. I am waiting for my Rislone to do it's thing, then flush the engine with Toyota Oil System cleaner and refill with the 0w20, thereby starting from scratch and HOPEFULLY, eliminating the hesitation issue some have experienced after an oil change. It would seem that those using the Toyota 0W20 have not encountered the issue. I also will only use the Toyota oil as it seems they have the necessary additives to work well with the VVT-I system and overly-sensitive knock sensors in our cars. I will not tempt fate again by using another brand of oil or viscosity. Also, with the 5W20 oil, I was adding a qt every 12-15 hundred miles but now havent had to add a drop since my last change 3k miles ago.

It's reassuring to hear what your dealers told you as it now confirms what DevH and I researched and uncovered. This is good!!

 

Lexus service writers and mechanics are not engineers and I would take whatever they say with a load of speculation.
If the knock sensors was pulling timing like crazy to cause hesitation it would throw a check engine light eventually. What we are dealing with here is VVT issues with varnished deposits that is not allowing the oil to move the VVT sprocket effectively since it is oil pressure dependent. It's most likely the source of hesitation and it's documented. Using regular oil is the culprit and synthetic oil is the cure because it will keep the engine deposit free.
You do not need to use Toyota oil or even a 0W-20 grade but I would stick to Toyota oil because it's the best oil for your Toyota because of it's formulation. The formulation is specifically designed to match the metals and seals of the car and because it's a lighter weight oil they formulated it heavily with anti-wear additives that is in excess with whatever Mobil 1 is formulated with.

 

The cold or hot issue aspect of oil is not really relevant with modern oils especially with synthetic these days.
There should be no difference in viscosity between the two oils as both are 20 weight.
The only difference is that one can flow better at low temperatures.

The only time you should use thicker oil is in an application where you will be towing or racing. What happens is the oils viscosity at a very high heat will thin down to match the clearances giving enough adequate protection between moving parts. Thicker oil is a band aid for very high temps that most all of us will never see.
If you use thicker oil where you are not needing it then you will create unnecessary fluid friction.
Because synthetic oil is thermally stable and the fact that modern cooling systems are more then adequate, you don't need to worry about the oil weight.