Using Delvac dino oil & had Rotella in it in the past. Does synthetic make a difference in wear & MPG? If so, Synth Mobil or Rotella? Pulling 14K when the truck is driven. Does

I use nothing but the Delvac 1300 15w40 in the
2000 F450 7.3
1989 F350 7.3
1995 5.9 cummins

Excellent engine wear protection.

I have a 2000 7.3, use it for everything from side-work to pulling 10k-12k to the track. Owned it since new and it has had a diet of Rotella, both dino and synthetic. I have never been able to tell a solid difference between the oils and certainly no mileage increase. It might run a bit quieter for a longer period on the synthetic but whether that's a wear factor or not, I couldn't say.

Delvac is good oil and has rebates now.
https://mobiloil.com/en/promot.../40-off-mobil-delvac

Synthetic or not, they seem to "like" lower viscosity in the winter time. I guess it has to do with the HUEI system. I just use leftover 15w40 from work (Delo) during the summer; winter time 10w30 or 5w40 whichever I can get my hands on. MPG improves with 5w40 compared to 15w40.

Once the temps drop into the 30-40's around here, I keep mine plugged in - sure helps that first start in the morning.

Delo 15/40 from Costco, 450,000 miles and still going.....Bought it new, changed oil every 3500/4500 miles.

both of ours start a little easier with 10/30 or 5w40 in the winter. I don't plug mine in, never needs it. Dad plugs his in but his relay is junk. Mine is a stancor relay. I have in the past just to make sure the heater works (and it does). With lower viscosity fluid, the engine seems considerably less cold natured, a LOT less sluggish before it's at operating temperature. Dad's is an OBS and with 15w40 in the winter, it wants to "romp" about 10 times before it smooths out. With lighter oil, it starts right up--perfectly smooth; well as smooth as a T444E is going to be. NOTHING like the newer stuff.

Both are good oils, Most important thing is that you change the oil often and make sure you don't run low. I run rotella T4, and I used some hot shot secret sticktion eliminate on the last oil change. works great. I used the lucas the 2 oil change before and saw some performance loss. Could be just my truck didn't like it, My car does.