Dealership added the wrong oil

You can contact Toyota and report that unprofessional behavior, but screw that dealer. I wouldn't set foot in there again. In fact, I'd be posting the name of the dealer everywhere I could. What an idiot.

 

Just to be clear, I don't think 5W20 vs. 0W20 makes that huge of a difference. As I recommended to the OP, after a service appointment I'd check tire pressure and whether they overfilled the oil. That can make a bigger difference.

Toyota does recommend the 0W20 and my primary point is on a newer car, I'd always want what is considered optimal. When paying a dealership to change the oil, I'd expect them to use the primary, owners manual recommended weight. That would be my expectation. If for some unexplainable reasons it is not available or they have run out, at the very least I would expect warning and a conversation BEFORE any other weight is used.

Do I think running 5W20 for a cycle would make a huge difference in mileage or on any other measurable scale? No. Toyota even says you can do it, even if they do recommend changing back the next cycle.

 

5w-20 instead of 0w-20 is not going to hurt anything on the Prius. End of story.

 

Right - I get all that, cold oil = more viscous, friction is the enemy, etc. But that's not really my question. Especially in a warm season/climate, the oil is only "cold" (below operating temperature) for a few minutes at the start of each trip. After that, it was my understanding that viscosity is the same at operating temperature, so I don't see how the 0W vs 5W makes any noticeable difference.

I'm not saying you should use 5W oil; I use 0W-20 exclusively in my Prius. But I wouldn't hesitate to put in 5W if I knew my OCI would be summer-only! That's why I'm surprised - that people notice any difference with 0W vs 5W in a warm climate.

 

They probably just think that they notice the difference.

People are funny sometimes.

 

I'm saying it should always make a difference, at every temperature. Nearly every part in the engine and drive-train is bathed in oil, therefore viscosity is always a factor. I don't believe there is ever a point where it disappears.

 

But nominally, the two grades have the same viscosity when they're warm!

 

Ayup.

Of course it's still a factor, but are you saying it's different between 0W-20 and 5W-20, once the oil has warmed up?

Exactly! That's my point.

 

Well, I'm saying they aren't, but whether it has a measurable effect on mileage is another matter. As I said, small things count towards fuel economy on the Prius.

 

I'm afraid I'm more confused now... You're saying there's no difference between X & Y, but switching from X to Y might still result in a measurable change in fuel economy? Not trying to be a wise-@$$, just trying to understand.

 

I'm saying there's no such thing as "no difference."

However, proving "no significant difference" is another matter. If it made no difference, the 0W20 I'm using should give me the same mileage I get in the summer. It doesn't.

For fuel economy, I'll take whatever I can get.

 

Well said, Mitch.

 

My guess: What those people are noticing is 30% explained by viscosity difference (mainly before the oil is up to operating temperature), and 70% by placebo effect.

 

I purchased my 2012 Prius v a few months ago and saw the Mazda dealer I bought it from put 5W-20 in it. Took it in last week for an oil change and got 0W-20 this time. I drive the same route every morning to work and have been noting the mpg reading from Torque at the same point (2.5 miles in). I'm sure there is some mpg difference between the two oils, but I can't detect it from my drives.

 

I'd suspect 5W20 is slightly thicker than 0W20 at any temperature. That the increased thickness is most pronounced when cold, but they're never identical in thickness, even at the high temperature end.

 

Yeah, but let's not lose sight of the fact that the viscosity difference between 5W-20 and 0W-20 is trivial compared to the differences in viscosity due to temperature variations as weather changes, or between Calgary's climate and South Carolina's, for example.

 

Ha! I'd probably call it "confirmation bias" in this case, but I completely agree.

 

If alcohol had any lubricating qualities, I'm sure it would greatly improve fuel economy if it were used as an engine oil, because of it's much lower viscosity.

Anyone who has tried running in deep water knows about viscosity. Imagine what it would be like trying to run in engine oil. That explains why 0W20 oil should provide better fuel economy than 5W20.

 

I once tried to support local business in the town where I lived, but they didn't support me. I was asked to pay $99 for a pair of shoes locally, but when I went to the city, I found the exact-same shoes for $29. If you have to ask big favors of your customers all the time, you don't deserve to be in business.

I didn't get a manual with my car either, but they promised me one. I didn't get it for 6 months, because they said it had to be specially printed. Not very impressive.

 

If you're talking about running the car in a cold climate during the first few minutes after it's been turned on, I'd agree. But you seem to be saying that there are inherent viscosity differences all the time when using these different oils. My whole point is that most of the time that most cars are used, they're at operating temperature, and that time spent running at cold temperatures is minimal. You seem to be missing the whole point of multi-grade oils, which is that two different oils can be effectively a DIFFERENT VISCOSITY when cold, and the SAME VISCOSITY at operating temperature. Thus these two oils are THE SAME once the car is running. Unless you drive primarily in short trips, letting the engine completely cool between each, the difference should be very small.
Here are a few different sources showing SAE specs for engine oils:
Motor Oil Viscosity Grades Explained in Layman's Terms
Viscosity Classifications

Note in both sources that the kinematic viscosity of both 0W and 5W oil is 3.8 mm^2/s at 100 degrees C, exactly the same. 10W and higher have slightly different viscosities at 100C, but 0W and 5W are the same.
If you know of any data suggesting that 0W-20 and 5W-20 oils have a different viscosity while in regular use, please share it.

Having said all this, I'll say once again that I'm not going to start using 5W in my v right now! Warmup time is still relevant, especially at our current sub-freezing temps, and I like to follow mfr's recommendations whenever possible. But if I lived in a consistently warm climate, or if I was doing an oil change that would ONLY be used in mid-summer, I would not hesitate to use 5W.