I just don't understand why you would run a 10w instead of a 5w if that is what Toyota recommends. The only difference in a 5w-30 and 10w-30 would be cold start flow. Why not have the extra protection with the 5w oil? There is nothing wrong with 10w-30 but 5w-30 wil do everything and also give you more protection at startup. With that being said, if an older car recommends a 10w I would run what they recommend. I believe most cars today are recommending 0w-20, 5w-20, and 5w-30 mostly. I'm sure there is exceptions to that though.

 

I've just been told that 10w 30 is thinner than 5W 30. And in the summer time thinner is better. And with my old car, I never had any problems using 10w 30 all year round.

This is my first import, and still learning all of it's idiosyncrasies. I've always heard that japanese cars are much more reliable than american cars. So I figure, if what worked pretty good with my old Pontiac, shouldn't be a problem at all with the Camry. And the guy I bought it from said he's been using 10w 30. And the car is still running great.

 

Here is a basic idea what the viscosity means on oil. The first number like 5w or 10w if basically how well it flows at startup temp. The lower the number the better it flow or thinner some say. The second number is how well it flows at operating temp. Most cars are designed for a 30w or even a 40w in some cases. The reason we use multigrade oil is to give us protection at startup. There is no way physically a 10w can flow better than a 5w at startup. So, a 5w-30 is going to flow better at startup but perform the same as a 10w-30 once at operating temp. If you live in an area that gets very cold in the winter you can even switch to a 0w-30 for more protection at startup. One thing that always confused me was when looking at room temp. oil it seems thicker than warm or hot oil drained from a car. Two things happen. When oil temp is warmed up it gets thinner. This has nothing to do with the flow rate or ability to protect your motor. Also as oil breaks down it gets thinner. Don't let you eyes deceive you. Don't go by what it looks like as far as thin or thick to the eye. The rating is for when it's working in the motor.

 

Ah, so I've been misinformed, or I've perceived it the wrong way. Thanks for the quick lesson on oil viscosity. So basically, if I wanted to, I can just run 0w30 all year round, even if the Toyota recommends 5w30?

 

Yes you could. The only thing is 0w-30 is synthetic only. Atleast I have not seen 0w in conventional oil. Therefore cost becomes a factor. If you are out of warranty you can offset the cost of synthetics with extended oil change intervals. There are people going 10k to 12k miles on synthetic before changing. That's a bit long to me but you can safely go 7.5k miles without worrying. The reason is sheer stability. Synthetic oil does not sheer and break down nearly as fast as conventional oil. My plan with my new camry is conventional 5w-20, which is recommended, until warranty is up. Then, I will switch to 0w-20 synthetic and change to 7.5k intervals.