So I’ve been running my old 5.9 Cummins for years, and I’ve always just topped up the coolant when it looked low. Now I’m staring at a jug of Fleetguard ES Compleat and my shop manual, and I’m realizing I’ve probably never done a full flush and fill correctly. I guess my question is, if you’ve switched to an extended life coolant, did you notice any difference in how the engine ran or how often you had to mess with it? I’m just worried I might be overlooking something simple.
Switching to extended life coolant years ago left the engine looking steadier and the temps felt calmer, but the difference was small and steady rather than dramatic.
From a maintenance view the real lesson is flushing to remove old deposits and keeping the inhibitors in balance so the system stays corrosion free with ES Compleat.
I am skeptical about big claims and on a 5.9 Cummins I still top up and monitor the level, the long life coolant may help but it is not a magic fix.
Some people frame this as a fluid choice issue but is the real point the need for a proper flush and bleed?
Reading the shop manual you will see there is a method to flush and fill to spec and mix the correct ratio with extended life coolant.
I like to treat the coolant like a character in a story and see if it shows up as clear or murky and the ES Compleat approach invites a longer stretch between changes.
If the system feels fine now maybe the test is a long drive and watching for color changes on the gauge rather than chasing a perfect mix.