C15 Synthetic or Not?

I would stick with rotella 15W-40.
I always heard if there’s a place to leak synthetic will find it.

 

I’ve used T6 forever in a C15...... fix the front cover.
It was probably leaking before anyways.

 

First where's it leaking on the front cover ? Crank seal probably wasn't part of over haul if inframe. Probably ready to leak from age. Leaking from behind fan hub mount the one stud (top driverside) common issue of leaking. Two ways to fix. Cheap way,pull stud clean stud and hole use silicon adhesive (not to much) put on stud threads and install. Let it cure and it will stop leak. Or expensive way remove front cover and replace front cover and plate gaskets.

 

Always use synthetic if you own it.

 

I switched to synthetic blend oil (shaffers) and no leaks.

 

Try to locate your “engine manual” online, which is not the same as your truck manual. There should be a section about engine oil types for your engine. I’d stick with what they recommend.

I personally use synthetic blend for my DD15 engine (2013 model). Full synthetic is very expensive.

 

Exactly this!
I used to run T6 in everything I owned, when I purchased my truck eith a 2WS Cat there wasn't a drop of oil anywhere. Even on the 2000 mile drive home nothing. Swapped it over to T6, it was like I drilled holes all over the thing. I couldn't keep the oil in it. Went to Mobil delvac 1300... No leaks.