I am planning to buy some Mobil1 for my first oil change, and was thinking I'd use 0w-20 synthetic as per all of the recommendations I've read on GH, but noticed that Wally also has 0w-40 synthetic, and wanted to get opinions on the downside (if any) of using the 0w-40.

I live in Arizona, which is known for its heat and my concern is that the 0w-20 won't protect as well in the summer heat as the 0w-40.

If I'm not mistaken the 0w-40 should be able to get to critical engine parts as easily as the 0w-20 during startup, but I'd like a weigh in from those in the know.

For reference, I'm not a very heavy driver, having only 3250 miles on my '07 Camhy since picking it up in Sept. '06. I will be sticking to a 5k oil change interval on the car.

I would use the 0-40 if I lived in your area What does Toyota recommend?

Here is a link to some corvette guys discussing 0w-40 oils:

http://forums.corvetteforum.com/show....php?t=1394289

What oil are you using Larry? As I recall, you were using 0w-20 Mobil1...you live out here in the heat as well - any switch or sticking with tried and true?

Engines get very hot operating anywhere. The problem with using the 0w-40 is the way the hybrid engine turns on and off. If the oil has reached the 40w and has not cooled enough to be the 0w (or5w) again then when the engine restarts periodically the oil can't pump up fast enough. My recommendation if you are concerned about extreme summer driving is the 5w-20 because it starts out a little thicker but that's okay because the ambient temperature keeps the engine warm enough even when the engine is off in the summer. The advantage is that it doesn't get so thick it can't pump rapidly when needed.

I'm still using the Mobil 1 0w-20 and cannot see a compelling reason to switch....

Now, if you come across something that says 0w-40 both can AND will increase fuel efficiency over 0w-20, then let me know. That would sway me.....

In the Corvette forums linked above I recall seeing something about the oil breaking down when it has such a disparity like 0-40 as opposed to a smaller temp range of 0-20.

Larry, if you're still using 0w-20 Mobil1 through the summer months, that's good enough for me...I was just curious if anyone had any insight into that 0-40 weight stuff.

Thanks all for the replies.

Why do they make 0-40? I think it is for use in extreme climates? I think ,however that Mike hit the nail on the head!