IMPORTANT QUESTION
 

Where i live, the toyota dealership only has 0W-40 and 0W-50 (both synthetic).
The guy there told me that its ok to to put 0W-50 in. Is that true.
I dont know if this makes any difference but in summer the temperature here gets up 55 degrees C or 131 degrees F, it can get really dusty, and it can get really humid.

*and i cant take the car anywhere else for service or theyll void my warranty*

Hell no.
Engine operating temperature is around 100C and there is no active oil cooling stock so it wont matter what kind of ambient temperatures you experience, you wont see much temperture rise to justify going 50wt or even a 40wt oil. Most people still have that "thicker is better" mentality. I'd probably go for a 5W 30 max in those kinds of environments

The problem is that they dont have any :(

but would it hurt the engine?

Theoretically you can run any grade oil you want, you just won't get the fuel efficiency of the intended design with a heavier weight oil.

In the long run the key is to maintain a certain oil pressure. As your oil pump ages, you want to maintain pressure by going with heavier oils. And if you track the car, temps need to be kept in check via an oil cooler.
That's all.

-alex

90% of engine wear happens in the first 20 or so minutes after start-up because oil is cold and ALL grades of oil are way to thick. Going with a 40/50 wt oil will make the start-up viscosity much thicker due to the shape of the viscosity v temperature curve. Lets say ideal oil viscosity is 10 Cst, a 20wt oil will be 5 times thicker than ideal (assuming 40C temperature) and a 40wt will be around 9 times thicker and it gets worse as temperatures dip under 40C oil temp (these are very rough values). This increase in viscosity may lead to slightly more wear (probably not significant with your ambients).

The issue I would be more concerned about would be reaching maximum oil pressure before redline. Thicker oil = more oil pressure for the same flow and if oil is thick enough to reach maximum pressure at say 4000 rpm, you wont receive more flow after that point and hence no more extra lubrication. thinner oil = less oil pressure for same flow and you are able to continue lubricating at higher rpms.

There are other potential issues with bearing clearances etc. but Im probably making it sound worse than it really is, That being said on this car i would never put more than a 30wt unless I know oil temperatures will be over 110C consistently (track) and if you were to go to a track you probably should have an oil cooler for such a hot running engine anyways.

How about 20w-50 or 5w-40?

You should ask them to put in the 0W 40. Those higher W numbers would not be a good idea to use.

Bear in mind, though, that this is actually Toyota's problem not yours during the warranty period! If the dealer installs it and there's a problem Toyota has to honour that warranty.

I would look in your manual, there should be the required oil for your car in the country it is run in. That is what will be covered under warranty. The dealer should carry the proper oil for your car for it to stay in warranty....

-Mike Paisan

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The first number (0w 5w...) is generally a representation of the level of refinement of the oil rather than the difference in viscosity at 40c. Some 0w30 oils are thicker than 5w30 at 40c. The higher the initial number, the less refined it is. 10w and above are dominated with mineral oils. There are some "synthetics" that may have that viscosity however The definition of synthetics is very vague, many oils are labelled fully synthetic when they aren't even 8% synthetic. Stick to 5w and under I'd say, a 5w 40 would work much better than the 10w60 now. It's hard to comment on the ideal viscosity when we don't know what kind of oil temperatures you are experiencing though.

As for the warranty issue, the Toyota guys don't sound like they know what they are talking about and tbh I don't think they care too much aswell. You could probably run the car at almost any viscosity and not have the engine die within warranty period.

Go to a Subaru dealership and get the oil of them

PS they cant void your factory warranty for getting it serviced somewhere else. They can void the dealer extended warranty though

Here is a breakdown of what oil grades mean:

The "W" stands for "winter" and refers to the viscosity of the oil at colder temperatures. As @504 said, the majority of engine wear happens in the first 20 minutes after start up because the oil has not yet coated the engine parts, causing more dry friction.

A lower first number means a higher viscosity. Higher viscosity allows the oil to flow faster, but provides less lubrication. Remember, this is upon cold startup only.

The second number refers to its viscosity after the engine has been running for a while.

So what you're looking for is a lower first number so that you minimize dry friction (which cause the most wear and tear), that eventually becomes less viscous so that good lubrication is provided. Higher initial viscosity prevents less damage to the engine. This is why people are recommending getting a 0W or a 5W at max. Then, as the engine warms, the oil will become thinner and more protective.

Even if the temperature is never low where you live, you need something that will coat the engine quickly at startup. The 0W-50 is good for cold startup and will provide good protection after the engine is running, although performance and fuel economy may be reduced. Ambient temperature really shouldn't affect it, the only reason you would need the extra protection is if you were running the engine hard (i.e. racing, autoX, etc...)

If I missed anything, or made a mistake, please correct me guys!

Well, actually a lower first number means a lower viscosity, which means a thinner oil. The oil companies add polymers that actually thicken up the oil as its gets hotter(to a certain point), which gets the oil to the last number. So a 0W20 oil will flow like a 0 weight oil at startup, and a thicker 20 weight oil when running at 100 C.

A 0W20 will flow LIKE a 0 weight at cold temperatures. Would a 0W40 have the same flow at cold temps? no way. these are just classifications and the numbers only give approximate ranges. At 40C a 0w40 would have nearly twice the viscosity as a 0W20 so if you want to minimise wear on cold start ups you need to reduce both numerical values.