You can use the Shell Rotella T 15w-40 or the synthetic 5w-40. Either will be fine. You can also use Mobil Delvac. Despite what is preached here, according to Mobil, you can use Mobil 1 10w-40 in a light diesel engine.
That is a myth about not being able to switch back to a non synthetic oil if you use the Rotella syn. Of course, since it is alleged synthetics are more slippery as soon as you switch back to a non syn oil the advantage of having run synthetic will quickly be lost so thus you wasted your money. Oil threads always cause arm waving and general dissagreement /forums/images/graemlins/shocked.gif. Many claim there is no benefit to synthetic oil /forums/images/graemlins/wink.gif. Many of these same people will then tell you that you cannot use synthetic during break in because the rings will not seat because it is so slippery /forums/images/graemlins/crazy.gif. Think about that /forums/images/graemlins/confused.gif. Then it usually wanders off into a arguement about extended drain intervals and Amsoil vs Mobil 1 and everything else /forums/images/graemlins/frown.gif. Time and time again independent studies have shown Mobil 1 to be superior to virtually any other oil, most recently I read about a tests in MCN, Motorcycle Consumer News. Mobil 1 auto oil used in motorcycles retained more viscosity etc than any other oil tested (they did not test everything of course). Corvette, BMW and others come from the factory with Mobil 1. Harley Davidson now recommends a synthetic --theirs or Mobil 1. The thing is that a quality conventional oil like Shell Rotella or Delvac or Dello (Chevron) will perform well in the conditions most experience with their vehicles, tractors etc
Here is the good news, use the Shell or any quality name brand oil and change your oil and filter per the manual and you will be A-ok. I change my oil and filter every 50 hours in my tractors, 5000 miles in the cars and 2,000 on the bike, I run Mobil 1 in everyhting, I have been doing this since 1980 when I worked for a particular oil company. That oil company performed fleet tests on company vehicles as well as lab tests. Their oil was a conventional and it was at that time a fine oil, they came to the conclusion, however, that Mobil 1 was the superior oil to any tested. Of course, these results were not released to the public for obvious reasons. Oh, the Fram filter would be my last choice.
If you go with the Shell Synthetic Rotella 5w-40 you can use it in everyhting including your push mower, your cars and trucks and your BX, even your air compressor. If you go with the non syn 15w-40 it will be great in your BX and your Briggs pushmower but I would not use it in newer vehicles that specify 5w30.
Confused, you might wish to retreat to the oil thread forum under general topics /forums/images/graemlins/grin.gif. J