Marvel's Mystery Oil year round.
Diesel Kleen White comes fall & winter.
And when it gets around 20 below zero or colder, isopropyl alcohol in addition to the Diesel Kleen White.
You may call me Doctor Overkill, that's okay, but I haven't had any fuel gel up or fuel lines freeze yet in Minnesota winters.
No engine issues in 300K+ miles. Other issues, yes, but never engine issues.