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Old 05-02-2020, 08:08 PM   #1
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Seneca DEF Concerns

Since we may not be using our Seneca much this year, we need to worry about DEF getting old in the tank. DEF is stated to have a life of 1.5 to 2 years, but high heat can reduce the decrease the life to much less than that. For those of us living in the south, we need to be concerned due to the summer heat. This is especially true if you have a full tank that has been there for an extended period of time.
I went by my Freightliner dealer today and asked if there was a way to drain the DEF tank and was told that you can only syphon the DEF out through the tank filler. From what I have read, this is not viable option do to the check valve.
Does anyone have a viable option?
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Old 05-03-2020, 04:22 PM   #2
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i know there is a filter on the tank sorry not much help
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Old 05-03-2020, 04:50 PM   #3
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Not sure on freightliner but every Peterbilt I have ever seen it is a straight shot into the def tank. Easy to slide a siphon hose In. I have done it multiple times my self at work. Only other option I see take the suction line off the top of the tank use a hose with a clamp and an electric 12v pump suck it out.
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Old 05-03-2020, 07:14 PM   #4
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You could also pull a few drops and test the DEF using a Refractometer. I have used one similar to this.

https://www.amazon.com/OTC-5025-Auto.../dp/B0054WI5KQ
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Old 05-03-2020, 08:19 PM   #5
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You could let it just sit and then check before you use it but if it deviates much off 32.5% you will need to find a way to get it out to put in new.
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Old 05-04-2020, 05:35 AM   #6
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You don't mention what chassis your Seneca is on. The M2 and S2, I believe have different DEF tanks (I could be wrong on that).

Also, have you crawled under the coach to verify there is no drain plug? I have found that dealers don't always know about the features on items they rarely service.
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Old 05-04-2020, 08:40 AM   #7
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I was under it yesterday; no drain plug. I have S2RV chassis. I has a very good shield under the plastic tank with very little area of the tank exposed.
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Old 05-04-2020, 08:48 AM   #8
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Here is the DEF flush procedure from the service manual.
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File Type: pdf Seneca DEF Flush Procedure.pdf (14.1 KB, 103 views)
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Old 05-04-2020, 09:46 AM   #9
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Quote:
Originally Posted by dramo77355 View Post
I was under it yesterday; no drain plug. I have S2RV chassis. I has a very good shield under the plastic tank with very little area of the tank exposed.
I crawled under the Accolade this morning and you are correct. That tank is enclosed in one heck of a metal shield with a heck of a skid plate on the bottom. I also did not see an exposed drain plug.
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Old 05-04-2020, 10:04 AM   #10
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Manual says it can be siphoned out the filler.
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Old 05-04-2020, 10:12 AM   #11
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The fear of someone introducing a foreign substance into my fuel or DEF tanks is why I replaced the caps with locking versions. Just something else to think about!
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Old 05-06-2020, 06:13 AM   #12
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So, what would be the disadvantage/results of old DEF and how would you know it had gone bad? Just asking for a friend.
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Old 05-06-2020, 07:33 AM   #13
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Nox emission codes. Def quality codes. Emission derates.
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Old 05-06-2020, 08:12 AM   #14
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Tell your friend that DEF can crystalize as the water dries and the concentration is out of spec. This would cause the emissions to be high. The primary concern is that the crystals could plug the system and cause the computer to put you in a shutdown mode and require your rig to be towed. That would be even worse if you are on the road and in the middle of nowhere.
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Old 05-06-2020, 12:03 PM   #15
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So if you siphon out the DEF From the tank won’t there still be some in the lines all the way up to the injection point? Will that cause an issue?
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Old 05-06-2020, 01:43 PM   #16
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Yest but hopefully you are starting the unit up and driving it regularly. The worst things to do with any engine is not to get it up to temperature and putting a load on it.
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Old 05-06-2020, 01:54 PM   #17
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If you start it up with an empty def tank To suck the lines dry will you set a code or just warning a light?
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Old 05-07-2020, 12:36 PM   #18
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Once you have syphoned out the old, add a gallon or two of new and take your RV for a trip. That will flush out old DEF in the line and replenish with the new DEF. Be sure to buy the freshest DEF (check the date) that you can find. That way you can reset the DEF expiration date on the DEF in your tank. We have a BBQ restaurant about 30 miles from our house that we will go and have lunch just get some time on the RV and generator.
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Old 05-07-2020, 12:38 PM   #19
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Starting on an empty DEF tank?

I would not try starting on and empty tank. The outcome is unknown, with a worse case of a hard stop light that requires a tow to the nearest shop......
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Old 05-09-2020, 12:12 PM   #20
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Quote:
Originally Posted by rgolding View Post
So, what would be the disadvantage/results of old DEF and how would you know it had gone bad? Just asking for a friend.
When I picked up my Seneca with Freightliner M2 it had not been driven for a year. When I stopped for fuel the engine light came on and the power was down substantially. I immediately took it to my local diesel mechanic. He drained the DEF tank and replaced it with fresh DEF. Has run like a top since. Short answer is you will be down about 25% on power. When the computer senses an exhaust fault, it reduces the output to 75%. When the DEF tank runs dry you will be reduced to "limp home" mode.
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