When to add DEF fluid - Chevy and GMC Duramax Diesel Forum
Alternative Fuels - Diesel - Additives - Lubricants Discussion of diesel, its various additives, oils, lubricants and alternative fuels IE: Bio-Diesel ect...

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post #1 of 36 (permalink) Old 03-22-2016, 08:28 PM Thread Starter
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When to add DEF fluid

I was wondering what people's habits are when adding DEF fluid. This is my first diesel that I have had to add DEF and with 15,000 miles I've only filled it up a few times. Got the message again today that it is low, but the previous times I let it go till the warning of speed limitations came on then added. My thinking on this is that since DEF does have a shelf life if I pretty much ran the system out I would have all fresh in compared adding a 2.5 every few thousand or so. Is there any harm in running the tank dry? I know you really don't want to run these newer diesels low on fuel because of potential increased contamination in a low tank. The times I have filled up it has taken five gallons. I have been going to the dealer and getting the AC Delco stuff just in case I ever had an issue. It's more expensive but who cares if it's $5 more I guess. This is my farm pickup so I almost never get 50 miles away from my house so it would be unlikely I'd ever get in a situation where it would actually be speed limited before I could get DEF.

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post #2 of 36 (permalink) Old 03-22-2016, 08:54 PM
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What you're doing 2.5 gals at a time is exactly what I did when all that was on my truck and it worked well, I never had a poor def fluid quality light. I also only used AC delco. My truck didn't get a whole lot of miles put on it on a regular basis, so that's the strategy I used. Wait for the warning message and add 2.5gals. I've seen a lot of dmaxes over in our Chevy shop with the def tanks being pumped out due to poor def quality, people constantly topping them off and or getting cheap def that's been sitting on the shelf too long. I know our chevy parts department purges the def every few months, if it's old it gets tossed. I'd keep doing what you're doing, like I said it worked well for me.

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post #3 of 36 (permalink) Old 03-22-2016, 09:00 PM Thread Starter
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Yeah my local dealer goes thru a lot of DEF and he keeps it in the back of the shop in a dark area. I have been tempted at times to buy some on sale DEF at the local NAPA or farm store, but there is just no way knowing how old it is. I'm sure it's fine, but you never know.

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post #4 of 36 (permalink) Old 03-22-2016, 09:02 PM
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Another reason to delete DEF lol
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post #5 of 36 (permalink) Old 03-22-2016, 09:50 PM
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I'm almost at 6k miles and I haven't had to add any Def fluid yet
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post #6 of 36 (permalink) Old 03-22-2016, 11:10 PM
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I use to add when id get the 1st warning. Use the DEF from the DEF pumps at truck stops. Much cheaper in price at 2.50-2.70$ a gal. Plus its just as fresh or fresher then the jugs from parts stores & dealers.


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post #7 of 36 (permalink) Old 03-23-2016, 08:32 AM Thread Starter
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Originally Posted by HD Dmax Machine View Post
I use to add when id get the 1st warning. Use the DEF from the DEF pumps at truck stops. Much cheaper in price at 2.50-2.70$ a gal. Plus its just as fresh or fresher then the jugs from parts stores & dealers.
Yeah the margin on that stuff must be insane. I mean it's water and some urea! It cost me $30 for five gallons at my local Chevy dealer. Nuts.

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post #8 of 36 (permalink) Old 03-23-2016, 08:37 AM Thread Starter
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Originally Posted by shibbby911 View Post
I'm almost at 6k miles and I haven't had to add any Def fluid yet
Seems like I've been adding every 4-5K or so. I haven't been all that impressed with the mileage, hoped it would be better. So far a lifetime average of about 14. My LMM was usually around 13 so it's slightly better, but was hoping for more. However, the LML weighs about 700 lbs more than the LMM so that does make a little difference I'm sure.

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post #9 of 36 (permalink) Old 03-23-2016, 09:06 AM
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I top mine off about every other week and never let it get low.

One thing I do is shake the DEF container up before adding any. I wipe the cap off to remove any crusted DEF off it before putting it back on.
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post #10 of 36 (permalink) Old 03-23-2016, 11:06 AM
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I usually wait until I get to the 300 miles to derate message and then fill 5 gallons. The dealer filled the truck once and I filled the next two times and I've never had a problem. I get the Blue DEF from my local Sam's Club. They move through it pretty quickly so I know what I'm getting isn't old and it costs about $22 for the two containers.

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