DEF Fluid when to add

[Screamsdaddy]

Hi all, purchased my 2019 Ram EcoDiesel May of 2020. I have only driven 4000 miles to date. My DEF gauge shows 1/2 tank remaining. Should I run the fluid to as close to empty and refill the tank then or may I top it off with fresh fluid? Since it is an 8 gallon tank I was thinking of adding 2.5 gallons. Still learning the tricks of the trade.

 

[John Jensen]

Hi all, purchased my 2019 Ram EcoDiesel May of 2020. I have only driven 4000 miles to date. My DEF gauge shows 1/2 tank remaining. Should I run the fluid to as close to empty and refill the tank then or may I top it off with fresh fluid? Since it is an 8 gallon tank I was thinking of adding 2.5 gallons. Still learning the tricks of the trade.

There's no good formula. It depends on how you drive. If driving low miles don't fill it as DEF has a short active life span. If you are a high mileage or towing driver fill it up. Unless it is under load the Eco does not use much DEF.

DEF is used during Passive regeneration. Here's what was once said by a reputable tuner:
Generally, the EGT’s will not get hot enough for a passive regeneration at unloaded highway speeds. Most trucks will never see a passive regeneration. However, when towing, carrying a full load, or driving hard the EGT’s can reach passive temps (700+f) and perform a passive regeneration.

 

[CAVEMANN]

John is correct on life span, everything I've found says it depends on temperature, and at temps around 100 it's supposedly about 3 months IIRC. I bought a refractometer on AMAZON for the DEF for about 26 bucks before I tuned the need for DEF out.