I have used 15-w40 rotella in my two vans (80k and 185k miles) in central/southern ca temps about 15k miles. No problems. Before that I used 15w50 mobil 1, but it's not available for reasonable prices around here any more. 

So anecdotally I think you're fine. Take an aspirin and move on.
 
Joe
Cayucos CA

On Mar 15, 2013, at 4:22 PM, Jeremy Stovin <jjstov@YAHOO.COM> wrote:

> AAAHHH!! My head is spinning!!  I am in Seattle. Summer temps are 60-80. Driving to San Diego in July. Can we agree that 15w-40 will be just fine for me? Taking an aspirin. 
> 
> Sent from my iPad
> 
> On Mar 15, 2013, at 2:43 PM, Dave Mcneely <mcneely4@COX.NET> wrote:
> 
>> ---- Karl Wolz <wolzphoto@Q.COM> wrote:
>>> Record back in the sixties was 118. Maybe your memory added ten.
>> 
>> that's not that much hotter than here.  We had 115 last summer, and 112 and over for days at a time.  Similar the previous summer, except I think the hottest was 114.  Central Oklahoma, not far from Oklahoma City.  But, we have winter, and not just in the mountains (we don't have any of those, though there are ranges of hills that bear the name).
>> 
>> mcneely
>> 
>>> 
>>> Karl Wolz
>>> Sent from my electronic umbilicus
>> 
>> --
>> David McNeely