I came across a bargain on some
Schaeffer's #131 and have been working my way through it at a fairly high dosage rate (not that more is better, but because of partial tank fills and wish to have the minimum dosage present). Did some short hauls with a 7k trailer and now can't find a bit of smoke/haze when winding it out in Fourth to redline.
Fuel additives may "work best" when the motor is being asked to perform, not loaf. I tend to think the better ones simply help the diesel to burn a bit better
and that this shows up only under heavier fueling demand. I noticed on my old big block gasser car that this also "seemed so".
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