5w40 in the NB1, or 10w30? Synthetic.

So, hot temps in the SoAZ desert, last week was 113-114, and I was going to run a good synthetic rest of summer. 

But, local parts store has no synthetic 10w40, which is what I normally run (dino in winter, synthetic in summer).  

So, lighter cold weight or lighter hot weight?  

I'm thinking 5/40, I usually baby the motor when cold anyway, but would 5 cold be too thin?

Or run the 10/30?

What sez the engineer types, and or Keith?

so from a lubricant standpoint, the rule of thumb if you do not have the preferred viscosity, you can go to the next thicker fluid.  To test for the CC (cold crank) which is looking for the lower number value and effectiveness, a 5W will be tested at -30C IIRC. a 10W is tested at -25 I think... I'll have to do some research. In either case, the base viscosity (30 or 40) is what you're going to be looking at for your climate. 

Why do you think you need thicker oil? Are you seeing wear? Low oil pressures? 

*edit*  Duh, I read this as ND1.

In reply to red_stapler :

?  Not in an NB that i recall. 

Doing a little reading on Bobistheoilguy, several guys running 5wXX, seems like 5w40 would be fine. 

Bobzilla, I switched from 10w30 to 10w40 years ago, not real sure why, probably car seemed to be run a little cooler/better in the hotter months, never went back to 30.

Now,  30 synth is probably fine, but I think I'll run the 5w40.

Auto-x tomorrow, supposed to be 104 at peak heat (we should finish before then, but will be within a couple degrees of that. 

Mazda would tell you 10W30. 

Doesn't really matter what the max outdoor temp is, your cooling system should be controlling the operating temp. 

In reply to Keith Tanner :

I saw that 10/30 was indicated, went with that. 

I can't remember now why the h-e- double hockey sticks I'm thinking about 40 with this car. 

They say as you age the mind is the second thing to go.   Can't remember the first. 

Thinner cold viscosity is so that you don't have to baby a cold engine, since thicker oil mostly just blows past the pressure bypass until everything is up to temp.  The oil isn't thinner when cold, a 5W40 means that the oil is as thick as cold 5wt when cold and as thick as hot 40wt when hot.

IIRC, 0W60 has an almost completely flat viscosity curve.  It costs a little bit more than 5W40 or 10W30 though!