DEF CONSUMPTION

By law all DEF will have a shelf life of 2 years . After that you dilute it 10 parts water to one part DEF and spray it on your lawn , per the manufacturer .
Sunlight will shorten shelf life .

DEF consumption is a percentage of fuel consumption. The more fuel you consumer per mile the more DEF you will also consume. With my Duramax I get roughly 1000 miles per gallon of DEF when not towing and roughly 750 miles per gallon when towing.

When traveling and in general I get DEF at the pumps which is available at most truck stops and many Shell gas stations that sell diesel. That way I can get the DEF tank to 100% full and the DEF is fresher.

DEF is most expensive and least fresh when you buy it in the 2.5 gallon plastic containers at a big box or chain store. Buy it at the pumps and there is no question as to how fresh it will be. DEF also degrades with temperature and exposure to sunlight so sitting underground at a fuel station is a good way to keep it in the best possible condition until it goes into the tank on your truck.

Fresh DEF is enough of a concern that the feds are moving to reduce the maximum allowed size of the DEF tanks on the big rigs so that they will be getting fresh DEF each time they fill up the diesel fuel tanks.

oldtrojan66 wrote:
Don't want to hijack thread, but what does bad DEF act like?

A Poor DEF Quality message appears in the DIC. If it's not corrected within I believe it's 200 miles the truck will start speed limiting itself eventually to limp mode (4 mph).

Bad NOX sensors will cause that message to appear too.

I fill mine at least once a week when driving that truck.

N-Trouble wrote:

Roadtech wrote:
I wish you didn't have to go under the hood to add DEF on a Chevy. Having it next to the fuel fill like Ford does is so much better.

For something you fill two, maybe three times a year? Really?

it is more convenient when filling at a truck stop which I do when towing.

wrenchbender wrote:
This is a general question to anyone with a Duramax that requires DEF.How far in normal driving will the 5 gal of DEF last before the warning light appears?. Also Where are you purchasing the DEF?. I am contemplating a new Duramax and getting horror stories from a few GM owners.

I don't have a Duramax, but I just used 2.5 gallons on a 1300 trip from NY to FL under load. I buy the Peak brand from Walmart. No issues.

I am on board with it under the hood. There is another thread in here where a guy got help from his insurance company after he pumped DEF into his fuel tank. He said the insurance adjuster said they where getting around one call a week for this same issue. For me and the miles I drive (which isn't a lot) I like it where it is at.

N-Trouble wrote:
For the average person who drives 15k mi or less a year under the hood fill is ideal and a bit more idiot proof. I could see where high mileage fleet drivers would prefer the Ford fill location but that is a pretty small population.

Or RVers who drive a lot of miles per year like me...

Travlingman wrote:

allen8106 wrote:

Roadtech wrote:
I wish you didn't have to go under the hood to add DEF on a Chevy. Having it next to the fuel fill like Ford does is so much better.

I like mine better under the hood. It's more secure. I read a post where some fool vandalized a Ford truck and poured motor oil into the DEF tank. The entire DEF system had to be replaced. I have also read a few posts where people have inadvertently pumped deisel fuel into the DEF tank because it was right next to the fuel filler.

I claim bull on pumping diesel into the DEF tank. How did they get the diesel nozzle to fit in a hole that is half the size of the nozzle?

It is the opposite. Several Ford owners have pumped DEF into fuel tank taking down the entire fuel system.

For the average person who drives 15k mi or less a year under the hood fill is ideal and a bit more idiot proof. I could see where high mileage fleet drivers would prefer the Ford fill location but that is a pretty small population.

allen8106 wrote:

Roadtech wrote:
I wish you didn't have to go under the hood to add DEF on a Chevy. Having it next to the fuel fill like Ford does is so much better.

I like mine better under the hood. It's more secure. I read a post where some fool vandalized a Ford truck and poured motor oil into the DEF tank. The entire DEF system had to be replaced. I have also read a few posts where people have inadvertently pumped deisel fuel into the DEF tank because it was right next to the fuel filler.

Doesn't the Ford fuel fill door lock when you lock the doors? Also, what's to keep someone from vandalizing the diesel fuel tank?