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Old 01-14-2019, 02:50 PM   #1
Winterbagoal
 
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Default The DEF fairy paid me a visit

Ok, here we go, please bear with me, as I want to be as thorough and detailed as possible.

We had planned to be somewhere farther south and warmer by now, but life got in the way, as usual. I noticed something odd yesterday, and thought I'd look for opinions from those more diesel-astute.

About 3 months ago, before the really consistent cold weather hit southwestern Ontario, I prepped the Navion for winter. Did my usual winterization procedure mostly following the owner's manual, with the exception of adding RV A/F, as I use the blowout method for the plumbing. Nothing unusual here. I also like to top up the fluids under the hood, so checked everything, and everything was within spec. I also topped up the DEF and filled the fuel tank with Shell V-Power Premium diesel. I should add, I'm never sure how long it will be sitting in the driveway (outside, no garage available), so I like to be ready to roll, if the opportunity presents itself. I like to exercise the chassis and generator whenever possible through the coldest parts of the winter, providing the roads are clear and dry. So, she's now ready to roll, should we actually get a chance to head south for a few weeks/months.

About a week ago, we took her out for a long freeway drive (130 mile round trip average speed 60+mph). We've maybe had it out a few times doing the same tours since I winterized, probably put close to 1000+ miles on it. It runs like a top, no problems, every time. When we get home, I fill the fuel tank and park it until the next opportunity to exercise the chassis. Last weekend I noted the DEF dash gauge was showing 7/8 full, as the tank is demarked in quarter tank increments. So the level was halfway between the full and 3/4 marks.

Yesterday's run was no different than the priors, except I happened to check the DEF level, and the gauge now is showing FULL? Right up to the top mark on the gauge. We did our 130 mile round trip, and over the afternoon, it dropped down to between FULL and just above the 7/8 level. Call it 15/16. It has been below freezing during the day regularly for the few days prior, and has been regularly below freezing overnight. However it hasn't really got down to the 12F level that I'm aware of overnight, although I haven't checked the local weather history to confirm.

So, did the DEF fairy pay me a visit? Or is this attributable to being right on the cusp of having frozen DEF in the tank? I was thinking maybe the upper portion of the tank had partially frozen, or that the DEF had expanded upwards in the tank as it approached it's freeze point and was hitting the sensors, causing the tank readings to show FULL when they're actually lower.
I've got it scheduled for an oil change at an MB Sprinter dealer this week, so will mention it. I'm going to ask them to measure how much DEF it takes, if they top it up it as part of the oil service.
Any other ideas, speculations, opinions?
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2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
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Last edited by Winterbagoal; 01-14-2019 at 03:16 PM.
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Old 01-14-2019, 07:14 PM   #2
4wheeldog
 
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by Winterbagoal View Post
Ok, here we go, please bear with me, as I want to be as thorough and detailed as possible.

We had planned to be somewhere farther south and warmer by now, but life got in the way, as usual. I noticed something odd yesterday, and thought I'd look for opinions from those more diesel-astute.

About 3 months ago, before the really consistent cold weather hit southwestern Ontario, I prepped the Navion for winter. Did my usual winterization procedure mostly following the owner's manual, with the exception of adding RV A/F, as I use the blowout method for the plumbing. Nothing unusual here. I also like to top up the fluids under the hood, so checked everything, and everything was within spec. I also topped up the DEF and filled the fuel tank with Shell V-Power Premium diesel. I should add, I'm never sure how long it will be sitting in the driveway (outside, no garage available), so I like to be ready to roll, if the opportunity presents itself. I like to exercise the chassis and generator whenever possible through the coldest parts of the winter, providing the roads are clear and dry. So, she's now ready to roll, should we actually get a chance to head south for a few weeks/months.

About a week ago, we took her out for a long freeway drive (130 mile round trip average speed 60+mph). We've maybe had it out a few times doing the same tours since I winterized, probably put close to 1000+ miles on it. It runs like a top, no problems, every time. When we get home, I fill the fuel tank and park it until the next opportunity to exercise the chassis. Last weekend I noted the DEF dash gauge was showing 7/8 full, as the tank is demarked in quarter tank increments. So the level was halfway between the full and 3/4 marks.

Yesterday's run was no different than the priors, except I happened to check the DEF level, and the gauge now is showing FULL? Right up to the top mark on the gauge. We did our 130 mile round trip, and over the afternoon, it dropped down to between FULL and just above the 7/8 level. Call it 15/16. It has been below freezing during the day regularly for the few days prior, and has been regularly below freezing overnight. However it hasn't really got down to the 12F level that I'm aware of overnight, although I haven't checked the local weather history to confirm.

So, did the DEF fairy pay me a visit? Or is this attributable to being right on the cusp of having frozen DEF in the tank? I was thinking maybe the upper portion of the tank had partially frozen, or that the DEF had expanded upwards in the tank as it approached it's freeze point and was hitting the sensors, causing the tank readings to show FULL when they're actually lower.
I've got it scheduled for an oil change at an MB Sprinter dealer this week, so will mention it. I'm going to ask them to measure how much DEF it takes, if they top it up it as part of the oil service.
Any other ideas, speculations, opinions?
The DEF level gauge isn't hooked up to a float or similar technology.
I have noticed that my DEF gauge does not reflect the tank being filled until I also fill the fuel tank. That seems to trigger a query to DEF level, and it will reset to full.
It then seems to track level by actual usage.
So......The level in your tank didn't change. Your Sprinter just acknowledged that it was full, when you filled the fuel tank.
The logic of this makes sense for those that fill the DEF at the service station. I generally fill mine at home, so it did confuse me for the first couple of times.
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Old 01-14-2019, 07:54 PM   #3
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Default Re: The DEF fairy paid me a visit

There has recently been another "DEF in the cold" (Ottawa) thread, and it caused me to read the owner's manual about "cold".
Here: https://sprinter-source.com/forum/sh...ad.php?t=72511

Messages 8 and 9 cover what the book (and DEF web pages) says ... basically it CAN freeze below 12 f (-11 C), and the Sprinter may not see a refill that freezes at the top of the pipe.

The bottom of the tank evidently has a heater, but it can take a while for the engine to warm it up.

--dick
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((as always: this post may go through a couple of post-posting edits... so maybe give it ten minutes before commenting))

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Old 01-14-2019, 11:56 PM   #4
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by 4wheeldog View Post
The DEF level gauge isn't hooked up to a float or similar technology.
I have noticed that my DEF gauge does not reflect the tank being filled until I also fill the fuel tank. That seems to trigger a query to DEF level, and it will reset to full.
It then seems to track level by actual usage.
So......The level in your tank didn't change. Your Sprinter just acknowledged that it was full, when you filled the fuel tank.
The logic of this makes sense for those that fill the DEF at the service station. I generally fill mine at home, so it did confuse me for the first couple of times.
I fill my DEF up at the Pilot across the river at the truck lanes, bulk DEF (only if they aren't busy with trucks). Your theory would make sense except that I always refill the fuel tank after every exercise session. So if that triggers the DEF level check, it should have been steadily dropping. It had dropped since the last DEF fill, maybe back in November, but then yesterday, it decided it had refilled itself sometime last week after the last exercise session and diesel fuel refill. Sorry, I didn't mention that I always park the Navion (or the other motorhomes I've owned) with a full fuel tank in the cold months. Fuel Tank Condensation-phobia.
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2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
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Old 01-15-2019, 12:11 AM   #5
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by autostaretx View Post
There has recently been another "DEF in the cold" (Ottawa) thread, and it caused me to read the owner's manual about "cold".
Here: https://sprinter-source.com/forum/sh...ad.php?t=72511

Messages 8 and 9 cover what the book (and DEF web pages) says ... basically it CAN freeze below 12 f (-11 C), and the Sprinter may not see a refill that freezes at the top of the pipe.

The bottom of the tank evidently has a heater, but it can take a while for the engine to warm it up.

--dick
Hey Dick. I was following that thread/topic, and saw those (your) comments, but I didn't have any of the other symptoms of FINNDIAN, like the starts remaining warnings. My vehicle was operating normally in every respect. Both Wawa and Ottawa, Ontario, are typically much colder than where I live and operate my Sprinter based MH. So FINNDIAN's extra issues make sense to me.
I'm probably toggling around the freezing point for DEF, a little above, a little below, as the temps in my area have been all over the map lately. We hit 34F this afternoon here, after a weekend of day and night temps well below that. If the heater is at the bottom of the tank, near the take up point, that would explain my problem in simple terms. It also makes sense that they would design things that way. DEF sensors higher up in the tank aren't thawing as quickly, and so the gauge level is unreliable. It did seem to normalize after about 2 hours of freeway driving, although I'm sure the level a week ago was a bit lower. Maybe the problem was affecting it back then, as the temps were fluctuating then, too.
We aren't supposed to see any real wintery weather until next Saturday, according to the weather people. I can hardly wait...

Thanks for your input.

EDIT: Just went out and started the engine, idled for a few minutes, and checked the DEF gauge - shows exactly where it was yesterday after the exercise drive, which I believe was the actual fill level. Current ambient outdoor temp 26F. Not low enough (according to the manuals) to freeze DEF, so it looks like the colder temperatures on the weekend is/was causing the misleading gauge readings. Worth noting for future cold weather operation, for us up here "in da frozen nord". My cab chassis doesn't have all the add ons to warm things up, I'm at the mercy of the basic fuel/DEF/whatever heating systems. Winnebago orders fairly spartan base units.

Another issue comes to mind as a result of these two "frozen DEF" threads.
Is it possibly a good idea to NOT fill the DEF reservoir, if the temps are going to go close to the DEF freezing point, to allow some room in the upper part of the DEF tank and/or fill pipe, for frozen DEF expansion? Water expands when it freezes, I'm assuming DEF does, too?
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2018 (2017 Sprinter Cab Chassis) N24V + 2016 JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
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Last edited by Winterbagoal; 01-15-2019 at 12:42 AM.
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Old 01-15-2019, 03:27 AM   #6
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Default Re: The DEF fairy paid me a visit

If you RTFM, it tells you what can happen to diesel systems in cold weather, fuel and DEF.
I'm pretty sure it's nothing more sinister.
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2018 (2017 Sprinter Cab Chassis) N24V + 2016 JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
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Old 01-15-2019, 05:56 PM   #7
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by Winterbagoal View Post
I fill my DEF up at the Pilot across the river at the truck lanes, bulk DEF (only if they aren't busy with trucks). Your theory would make sense except that I always refill the fuel tank after every exercise session. So if that triggers the DEF level check, it should have been steadily dropping. It had dropped since the last DEF fill, maybe back in November, but then yesterday, it decided it had refilled itself sometime last week after the last exercise session and diesel fuel refill. Sorry, I didn't mention that I always park the Navion (or the other motorhomes I've owned) with a full fuel tank in the cold months. Fuel Tank Condensation-phobia.

Well, again....The DEF gauge is only an approximation base on use, and not to be taken too seriously about 3/4 full. Why and when it decides that the tank is full is a mystery to everyone but the MB engineers that designed it.
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Old 01-15-2019, 06:56 PM   #8
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by 4wheeldog View Post
Well, again....The DEF gauge is only an approximation base on use, and not to be taken too seriously about 3/4 full. Why and when it decides that the tank is full is a mystery to everyone but the MB engineers that designed it.
That may be true in some cases, but mine's always shown full, whenever I've filled it, with or without any coincidental fuel addition. Whether it's a float, or fluid contact sensors, or whatever inside the tank, I think the determining factor in this case had to be temperatures hovering around the freezing mark of this critical and mysterious fluid that can make or break your engine's functionality.
Thanks for all the feedback, it's all good, and logged in the memory banks.
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Old 01-15-2019, 07:27 PM   #9
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Default Re: The DEF fairy paid me a visit

The Sprinter DEF tanks have electronic level sensors, but only a few (something like 3 or 5), so it gives a low-res reading. Between that, the ECU interpolates.
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Old 01-16-2019, 12:22 AM   #10
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Default Re: The DEF fairy paid me a visit

Quote:
Originally Posted by avanti View Post
The Sprinter DEF tanks have electronic level sensors, but only a few (something like 3 or 5), so it gives a low-res reading. Between that, the ECU interpolates.
Mine shows - Empty, 1/4, half, 3/4, Full - marks on the dash gauge, so 5 would be the better guess (maybe?).
I'm in the shop for some minor maint tomorrow, and will try to confirm.

Thanks.
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