it is the only "true" synthetic on the market and is the only oil OTC that I can find that is recommeded for BMW, VW(audi), Mercedes AMG.......can the 3.5 use the same oil?

 

While I "think" the 0w-40 is still a group IV, that's a BIG viscosity range for an oil to handle.

I'd MUCH rather use something like Amsoil in the proper viscosity range if you want to use a "100% synthetic" group IV type oil. I think there still a few other 100% oils out there.

 

thats the wrong viscosity for our cars. use amsoil or the German Castrol 0w30

 

Might not be the best but I also run 15w50 which seems to work just fine.

 

So if we are to order the amsoil what weight or the manufactuerer do we order?

 

I use 0W/40 Mobile1 in my G35 here in Florida. I would not use the 5w/30 as that multigrade is way too thin. Here in the extreme heat this weight is the way to go. I believe that the German castrol 0W/30 is a very thick oil as well. That oil is heavier than other 0W/30 synthetics. It is actually very close in thickness to the 0W/40 Mobile1. Both German Castrol 0W/30 and Mobile1 0W/40 are really equivalent to a "0W/35" if there was one. Some other synthetic oils are also good, but I like to go with what is accessible and easier to find. It's expensive, but it's worth it.

 

It's important to know the exact temperature that oil encounters at the bearings. The sump temperature is usually 10-25 F lower, depending on rpm and load.

A 30 might be 28 and a 40 might be 35 where it counts.
The owner should select the top viscosity based on extreme hot idle oil pressure.