I live in Southern California. Temperatures range from 40F at night to 98F during the day. What synthetic should I use.. 5W or 10W.

Also, for an auto transmission what transmission fluid should I use (Redline?).

Nissan Maxima SE 2002 (Auto)

First off tranny fluid doesn't come rated by 5w or 10w anything, your thinking off engine oil. So if it's engine then if I remember correctly 10W-30 has the bigest range of use, so I would go it.

Actually, 5W-30 has the wider range of use because its thinner in the cold... However, reading the lovely book that Nissan provides with each Maxima, shows that 5W-30 is "preferred" for all temperature ranges. It then states that if the ambient temperature is above 0 degrees F all the time, then 10W-30 is good.. Personally, in CA I'd use the 10W-30 because it will be thicker on cold start ups (or when car hasn't been used for a while) and protect better until the oil reaches operating temperature. However, with synthetics like Amsoil and Mobil 1 that don't use thinners in the 5W oil, the protection is about the same at cold start up so that you are still protected.

???? How did you come to this conclusion? I am not trying to flame, just seems contradictory to everything I have read on the subject so far. I thought you would want a "thinner" oil (I.E. 5W- XX vs 10W-XX) for cold weather pumpability and the 30 that give the hot weather protection of a 30W?

I wonder where Bill is....I want to prove I actually read these oil threads almost like religious text!

What you're missing is the California part. It just doesn't get cold there. With a low temp of 40 degrees, I would definitely use 10W/30. 10W flows fine at 40 degrees and you will have a slightly thicker oil when cold than a 5W/30, which will actually reduce wear at startup since a heavier oil at cold temps is being used. The example of not running a car for a few days is a good example. As long as it doesn't get below freezing, using 5W/30 doesn't offer any advantages over a 10W/30.

I'm always here and always monitoring.

1BADMAX... I didn't say 10W-30 was a type of transmission fluid!

The term "ALSO" was used...

Very funny... since on my other post you also said "By the UDP has nothing to do with the y-pipe"...

You need to read my posts better, your making me sound like an idiot. I didn't think a UDP had anything to do with a Y-Pipe and I didn't say tranny fluid comes in 10W... Are you doing this on purpose

[Homer] DOH! [/Homer] So close and yet so far....must keep studying...

I'm in Cali too and I use Mobil 1 10W-30...

Okay so I read this one wrong, but from the looks of the other post it did appear that you were saying that none of the mods would be beneficial since you didn't have a y-pipe. Hell who knows maybe i'm the idiot...lol.

talking about catback in specific but whatever.

so 10W-30 is perfectly fine even if sometimes it reaches 37F?

And is redline tranny fluid good for auto?

and where the hell do i buy Amzoil.. is that what you people recommend?