AdBlue heater

roni024

Veteran Member
Joined
Mar 31, 2007
Location
Syracuse, NY
TDI
2015 Passat TDI SEL DSG
As we all know, the fuel economy of our TDIs drops in the wintertime. This can be attributed to many factors, some of which are winter blended fuel, and added load on the engine from heating the cabin etc. To my understanding, the heater in the AdBlue tank is an electric resistance heater which can place quite a draw on the vehicle's available current.

Has anyone ever thought about running a coil of coolant lines into the urea tank to reduce the amount of electric heat needed to warm the def fluid? Correct me if I'm wrong, but I'm assuming the in-tank heater senses the temperature of the liquid inside the tank, and does not go by the ambient outdoor temperature. Any thoughts?
 

Shife

Veteran Member
Joined
May 8, 2015
Location
Michigan
TDI
2015 GSW SE DSG White/Beige
That synthetic urea is pretty corrosive. I would think the cost of materials and time to make this work would probably exceed any fuel savings it may produce. It's a neat idea though.
 

roni024

Veteran Member
Joined
Mar 31, 2007
Location
Syracuse, NY
TDI
2015 Passat TDI SEL DSG
Good point about the metal reactivity.

I'm envisioning some sort of modification to the tank lid with a long helical coil of a flexible metal (something like brake line with a large diameter) that sits inside the tank. The metal would need some sort of protectant on it to keep the def fluid from directly contacting the coil. And the connection to it would need lots of slack so the cap with attached coil could be removed for filling the tank without disconnecting the coolant lines.

Or maybe there's a better way to install the coil permanently without modifying the lid.

Or perhaps the fill port could be extended with a neck, have the lines enter into the side of that, and have the original cap above.

I haven't really looked into options for getting the coil into the tank. At this point it's mainly speculative.

Let's roll with this. Keep the ideas coming!
 

bmali98

Veteran Member
Joined
Mar 16, 2008
Location
Dunsford Ontario
TDI
O4 golf pd auto
Something to consider is rules of "free energy" or whatever. You're engine runs most efficient at x*C. If it takes longer to get to temperature because it's thawing def, it's less efficient. Also throwing benefits of liquid heating to the wind is the fact the electric heater will be loading the engine from startup to thaw the def, aiding a fast warmup.

I wonder about circulating the def through a heat exchanger once thawed to/from the tank to maintain its temperature. That would mean the electric heater wouldn't kick back in and no need to hack a tank or sending unit for a heat exchanger.

I don't own one of these def cars. I work on trucks. All the big trucks with def I have seen use coolant but that might be a different kettle of fish.
 
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roni024

Veteran Member
Joined
Mar 31, 2007
Location
Syracuse, NY
TDI
2015 Passat TDI SEL DSG
Interesting thought about the engine coming to temp. Your proposal would make sense if there's a return line for the def back into its tank. I'm not sure of the setup on these cars. The whole idea of this alternate heating method for the def came to me in the cold season, so I'm not chomping at the bit to crawl under my car this time of year. ;)

But, if there was a return line built in at the factory, all one would need to do is make some sort of secondary loop between that and the supply, connect those to the heat exchanger to be installed, and tap into the coolant down stream of the thermostat to let the engine have first dibs at heat. Then, return coolant back downstream of that. Right?
 

bmali98

Veteran Member
Joined
Mar 16, 2008
Location
Dunsford Ontario
TDI
O4 golf pd auto
I'm not sure if you have a return line or not. Every truck I have worked on with this system has a return line and i think it circulates to maintain a stable temperature throughout the system. There must be some system in place to keep everything from freezing. Otherwise the def would freeze halfway to the scr chamber.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e
The AdBlue heaters are a few hundred watts. Modifying the system to improve fuel economy would be stepping over dollars to pick up nickels. It only runs in sub-zero (Fahrenheit) anyway.

The tank, the pump, and the lines are all heated electrically.

Read more starting at page 68 here*: http://vwts.ru/engine/cata/pps_941803_3l_tdi_cata_w_clean_diesel_system_eng.pdf

*the Audi SSP describes the system in more detail than the VW SSP, although it has a few differences, most notably the Audi's passive urea storage tank in addition to the active tank. The four cylinder TDIs only have the active tank.
 
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roni024

Veteran Member
Joined
Mar 31, 2007
Location
Syracuse, NY
TDI
2015 Passat TDI SEL DSG
VeeDub, I couldn't get the link to work. I tried to navigate through the page to find the pdf you referenced, but it's in Russian and a little cumbersome after translation.

If the heater is 300W, on a 12V system that draws 25 amps. To me, that is not negligible. If the heater only operates below 0degF, what would explain the drop in fuel efficiency during cold, but not sub-zero, temperatures? The same winter blend fuel that I get 40+ MPG on warm days will only deliver ~32 in the cold.
 

bballppaul

Active member
Joined
Jul 29, 2015
Location
Easthampton, MA
TDI
2015 Golf TDI S - Buyback, replaced with new 2015 GolfSportwagen S DSG
VeeDub, I couldn't get the link to work. I tried to navigate through the page to find the pdf you referenced, but it's in Russian and a little cumbersome after translation.
If the heater is 300W, on a 12V system that draws 25 amps. To me, that is not negligible. If the heater only operates below 0degF, what would explain the drop in fuel efficiency during cold, but not sub-zero, temperatures? The same winter blend fuel that I get 40+ MPG on warm days will only deliver ~32 in the cold.
Urea freezes at 12 degrees F, so the heater system will definitely be operating at anything under 12. I can't find the documentation right now, but there was technical documentation from VW describing the function of the urea-scr system in the Toureg, and I imagine the system would be similar. At anything under 20 degrees if I am recalling correctly, there is some heater functioning within the urea tank. If it is at near 12 or below, there is one heater that immediately thaws a small reservoir of fluid, and then a general heater that continues to heat and thaw the rest of the tank. It's done this way so that there is at least a little bit of liquid urea soon after start up. Additionally, the urea lines are all heat traced.

Additionally, as it gets colder, there is more general friction on moving parts. The transmission, wheel bearings, engine, etc. will waste more energy due to increased friction until the heat from that friction is able to warm the lubricating greases and oils. And yes, 20 degrees vs 40 degress has a big impact on this. Plus, you are probably running the heat longer.

All this could easily lead to an mpg drop from ~40 to 32 mpg. Especially if you have more stop and go traffic on your commute, as it takes a while for the diesel engine to warm up. A few weeks ago my mpg on the way to work was around 45 or 46 according to the computer. This is when we had a warming spell of 50 degrees. This morning it was 4 degrees. My computer said I was at 40 mpg this morning. I'm not suprised at that at all. And my commute is about 2-3 mi surface streets (but constantly moving) and then about 13 mi highway.
 

crazyrunner33

Veteran Member
Joined
Jul 11, 2006
Location
NC
TDI
'10 Golf(bought back)
Modifying the urea tank and messing with the heater is just an idea that's asking for trouble. It's cool in theory, but in practice, it's just adds too much complexity and a risk for error. Perhaps I'm biased because a close friend of mine lost his $60,000 dollar truck, it burnt to the ground due to an electrical short related to the urea heater.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e
VeeDub, I couldn't get the link to work. I tried to navigate through the page to find the pdf you referenced, but it's in Russian and a little cumbersome after translation.
If the heater is 300W, on a 12V system that draws 25 amps. To me, that is not negligible. If the heater only operates below 0degF, what would explain the drop in fuel efficiency during cold, but not sub-zero, temperatures? The same winter blend fuel that I get 40+ MPG on warm days will only deliver ~32 in the cold.
The fuel economy killer is the 1000 watt electric cabin heater and the post-injection of fuel to keep the emissions systems at the correct temperature during warm-up. Your DEF heaters are making a very minimal impact on your overall fuel economy. This is a solution to a problem that doesn't exist, IMO.

That said, don't let me stop you from butchering your car in a quest for +1 MPG in a very limited operating environment.

Try this link for the self study program: http://pics.tdiclub.com/data/517/840193_3_0_TDI.pdf
 
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bmali98

Veteran Member
Joined
Mar 16, 2008
Location
Dunsford Ontario
TDI
O4 golf pd auto
X2. That's a good read. Everything is only as needlessly complicated as it needs to be. A group of very highly paid engineers have done all the complicated work so we can just drive. For the second hand/10year market such as myself, think I would personally steer clear of all this. Time will tell if these systems hold up. I wouldn't modify these emissions systems unless to delete, and that only for cost reasons.
 
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