I bought my 05 magnum used and it was changed at Mopar using conventional 5-20. I drove with conventional oil for several tanks on a preset route which was all Interstate. I averaged 21.4 +/- 1/10 mpg. I swapped over to Mobil 1 synthetic and on the same route at the same speed averaged 22.5 +/1 1/10 mpg. Perhaps next oil change I will try Royal Purple and see if there is any additional mpg gain. But for those looking for the little extra economy, consider synthetic oil.

 

The results you got mirrored mine with my Buick--about 1.5 mpg. I'm interested in your results if you try the Royal Purple. I'm considering using RP when I get 5000 or 6000 miles on my R/T.

 

Even if you are not trying to get more MPG's synthetic is a good choice. Just make sure you retain the recommended oil weight (RT's it is critical), cost a little more but you can double and in some cars even triple the oil change intervals. Some people just pop off the oil filter and replace it at 3k and top off the leveluntil they get to the6k interval when they switched to synthetic.