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Old 05-26-2023, 08:33 AM   #1
Winnebago Owner
Join Date: Jul 2019
Location: Stuart, Florida
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DEF Age Concerns for 2020 Navion?

Vehicle is a 2019 Mercedes Sprinter 3500 3.0L 6 Cyl OM642 Winnebago Navion.

Concerned about the age of existing DEF fluid in the vehicle especially since we are based in Florida with elevated temperatures. Would like to extract the fluid currently in the tank and replace with fresh DEF. I have read every post I can find on this subject and am unable to locate any definitive procedure for doing this on the subject vehicle. Of course, Mother Benz manuals are silent on this subject as it is on so many other points of interest.

The DEF tank appears to be located behind the right headlight assembly and very difficult to access.

Hoping to obtain suggestions/ideas/comments from members of this forum who have more experience with the vehicle.

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Old 05-26-2023, 06:31 PM   #2
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Diesel exhaust fluid normally has a shelf life of about two years. However, exposure to sunlight or sustained high temperatures can compromise it. Any DEF purchased at a truck stop or auto parts store will have a clearly labeled expiry date — using DEF past this date can cause performance issues and potential maintenance problems.
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Old 05-27-2023, 06:32 PM   #3
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Removal of old DEF is not difficult on a Sprinter, just did mine about 3 weeks ago. I used an automotive suction pump to remove nearly all the DEF and replaced it with some fresh stuff.

Having previously owned a GM 2500HD with Duramax I had a DEF Refractometer to be able to test DEF. When I removed the Sprinters the old DEF I checked it just to find out it's status. I was surprised to see it just was under 32% which is fine, new fresh DEF at 100% strength is 32.5%.

You can pick up one of these on Amazon for under $25.00. Its a good thing to have in your tool box especially if your buying on the road from a truck stop. Simple to use, all you need is a few drops of the DEF you want to test. And you get immediate results.

To get the old DEF you can run a small line down the fill point and work it into the tank then simply suck it out. Takes about 20 minutes for the total process.

If you purchase a DEF Refractometer you can pull a few drops of your DEF out and test it this way you will know if its weak or needs replacement.

As I mentioned I removed 2 year old DEF that was actually fine but since this was a used Sprinter I didn't want to take a chance.
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Old 05-31-2023, 04:19 PM   #4
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I personally would not worry about any DEF in the vehicle. It is true DEF has and expiration date, but just loses potency with age. The computer calculates that and uses more DEF to compensate. So you just end up using more DEF .
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Old 05-31-2023, 07:03 PM   #5
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If yours fills from under the hood you have the 19.2l tank with a drain. The larger 22.2l tank fills from a side compartment and has no drain but is easy to siphon.
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Old 06-04-2023, 03:14 PM   #6
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Thanks so much for the responses.

ROADMASTER: How the heck did you get a tube down to the tank?? I am only able to push a tube about 18-20 inches down the fill tube and cannot reach the contents of the tank. Were you using a metal (rigid) tube or a soft plastic tube??

Please advise when convenient,
c thiggy
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Old 07-06-2023, 06:14 PM   #7
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Initially when I used a soft plastic tube (like pex) I ran into something I could not get past, I got further into the tank by rotating the tube while pushing and working it. It finally got it in and was able to remove most of the old def.

I had a friend recommend next time around to take about 1 inch of the plastic tube and melt a slight bend in it then when inserting rotate it as it is inserted and it should go right in.
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