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How far do you fill your FL Def tank?

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Stuart W

RVF Supporter
Joined
Nov 2, 2019
Messages
399
RV Year
2025
RV Make
Entegra
RV Model
Cornerstone
RV Length
45
Chassis
FL
Engine
Cummins
TOW/TOAD
Jeep Wrangler
I have filled mine to the red line in picture and still have 2 dashes on dash not reading, my Spartan had a line on the tank
 

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I keep mine between 3/4 and full but I don’t fill it to overflowing. The tank is black, not opaque, so I can’t see the actual fill line. I wait until the dash “gauge” has been on 3/4 for a while (down one dash) then add on 2.5 gal jug. This keeps it between 3/4 and full without flooding the top of the tank.

I don’t recall the reasoning but some time back it was said that “over filling” could lead to DEF header problems. I don’t know if that’s true, but its easy enough to manage it this way. That also might have been a Spartan specific thing.

I would agree that your tank level reading is incorrect, but I don’t know that its a problem. If it wasn’t still under warranty, I would just manage it as stated above to prevent it reading any lower. Since it is, it would probably be best to let FL check it out.
 
Last edited:
Like a car until the pump cuts off.
 
Like a car until the pump cuts off.
I’m actually using 2.5 gallon jugs so the only clicking I’m hearing is my back from holding the jugs 😉
The reason I ask, on my Spartan I one time overfilled the tank and had a Jeep covered in Def. This happened from filling on the drivers side at a truck stop.
 
It sounds like your prior coach had a leak somewhere. It should be a sealed system hypothetically. I would fill the new coach to the top with cap secure and see how it goes. I never had an issue and I always top off at the tank. Was never a concern.
 
It sounds like your prior coach had a leak somewhere. It should be a sealed system hypothetically. I would fill the new coach to the top with cap secure and see how it goes. I never had an issue and I always top off at the tank. Was never a concern.
I had checked into it at the time and found that Spartin actually had a fill line on the tank and the way the drivers side fill port was situated if you let it click off it would be higher than the fill line. Spartan had designed a vent in to the top of the sending unit plate that would vent fluid when overfilled this is what sparked my question in this thread. Sounds like the FL design is different.
 
I recall your setup had an option to DEF fill from either side of the coach. Does your 23 DSDP have this?
 
Spartin actually had a fill line on the tank
I loved it when there was a fill line. It was so easy. Now the DEF tank is black so can't see a thing. My standard MO is when I'm at ½ tank, I add 5 gallons and call it good.
 
Yeah, can’t see anything in the black def tank on the Superstar either.

On the trip to Ohio from Florida I went to 3/4 twice and just put the nozzle in and stopped when it clicked off. Gauge said full so I’m good with that process.
 
Thankfully I do NOT have one of those Diesel Exhaust Fluid tanks. Only have a one fuel tank and a propane tank.
 

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