I know the 3.0 calls for 0-20. Wondering since it’s summer would it be a good idea to throw in a slightly thicker oil so the oil doesn’t thin out too much?

 

You didn't specified the MY of your Jag but you indicated it's a 3.0 and I assume it's gas/petrol engine. . According to Amsoil use only 0w-20 all year round
https://www.amsoil.com/lookup/auto-a...gine-code-d-d/

 

Jag originally spec’d 5W-20 for the AJ126 V6, with 0W-20 in warmer climates, but later changed it to 0W-20 everywhere. At least, that’s what I remember though it was 8-9 years ago.

 

Pretty sure it was a little different to that, with 5W-20 in the early days (from 2012) then 0W-20 from 2014 but with 5W-20 for hot climates.
My point is you want thicker oil (higher viscosity) for hot weather not already thin oil like 0W-20.

 

I live in Indiana. It gets maybe 90s but that’s ab it. Might stick some 5-20 in there at some point

 

I used 5W-20 for the first few years, because that was all they spec’d originally.