As listed in the manual 5w-30.
You can use either 5W30 or 10W30...doesn't matter
Mine says 5w-30 on the oil filler cap
Your choice. GM does not specify which to use so it is up to you. Just make sure to use the recommended weight.
The manufacturer recommends that you use 10 W-40 weight motor oil in your 2003 Mercedes-Benz 500. You can use a lighter weight motor oil in extremely cold climates.
10-30 weight
5W30 weight.
R134a
You can use Synthetic oil at any time. You can even mix it with regular oil. Just be sure and use the correct weight.
Use 5W-30. It is the recommended weight by GM.
Most GM products, including the 2003 Trailblazer, take Dexron III transmission fluid. However, it is always a good idea to consult the owner or maintenance manual to be certain.
I use it on my 06 trailblazer I6 4.2
i got a 2003 model i gave it an oil change and advised to use 10w/40 synthetic.