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Go Back   TDIClub Forums > VW TDI Discussion Areas > Alternative Diesel Fuels (Biodiesel, WVO, SVO, BTL, GTL etc)

Alternative Diesel Fuels (Biodiesel, WVO, SVO, BTL, GTL etc) Discussions about alternative fuels for use in our TDI's. This includes biodiesel WVO (Waste Vegetable Oil), SVO (Straight Vegetable Oil), BTL (Biomass to Liquid), GTL (Gas to Liquids) etc. Please note the Fuel Disclaimer.

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Old November 6th, 2009, 12:07   #1
Diesel Addict
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Default Don't mix biodiesel with diesel in your tank.

I can see from the postings here that a lot of people are still not aware of this. Take it as good advice. Biodiesel has higher water solubility than diesel and when the two are mixed some water may drop out of the solution. This water is normally drained from the bottom of storage tanks by professional bio producers. If you mix the two in your fuel tank, there's a good chance you'll get some water in your fuel system. If you want to use bio as a lubricity additive or whatever, buy it pre-blended straight from the pump. Don't blend it in your tank!
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Old November 6th, 2009, 12:17   #2
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Interesting information. My 1981 Rabbit truck had a filter with a drain valve to dump water. Don't know if my 96 Passat TDI has a fuel filter.

Can someone tell me?
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Old November 6th, 2009, 12:37   #3
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This is called 'splash mixing' and is highly discouraged. The two fuels have just enough difference is specific gravity and polarity that water can drop out and the two fuels can form separate layers in the tank. Not good if one is trying to run biodiesel in winter.

All VW TDI fuel filters used up until the PDs have a water drain on the bottom of the filter. The TDI models did away with the little water separator tank with the electric water sensor back under the vehicle by the fuel tank.

John, you need to take a closer look under the hood! The fuel filter is in plain sight on the passenger side between the air box and the strut tower. If its not there, someone really messed around with your car.





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Old November 6th, 2009, 12:50   #4
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Quote:
Originally Posted by BKmetz
This is called 'splash mixing' and is highly discouraged.
BK: I don't understand your comment. I use one quart of soy-based biodiesel (bought from Houston Biodiesel) per tank of D2. I put the quart in after the D2 fill when I get home. I buy the biodiesel in 5 gallon increments and store it in a poly container.

Am I doing something wrong or not recommended?

Thanks,

Tony
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Old November 6th, 2009, 13:10   #5
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I edited my post to add more info on what happens.

Splash mixing does not guarantee the fuels will properly mix. There is some mixing, but it depends on the source of the bio, how the bio was made, water content, etc. There 'could' be stratification in the fuel tank, especially if the car sits a while after adding fuel. This is really a problem for people using bio in winter. A quart isn't going to matter but 5 gallons sure could. If you could see the inside of the tank you would see that most of the mixing occurs when you are driving around.

The water separation is mostly an effect of poorly made bio.
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Old November 6th, 2009, 13:13   #6
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Thanks, I saw your edits.

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Old November 6th, 2009, 13:20   #7
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On warm days like this I don't hesistate to pump a few gallons of B100 into the tank. If it's cold I just pump B50 or whatever I have already mixed. I would hope most would not be adding much bio into the tank when it's cold; that's when I'm splash blending in some D2 to give me insurance from gelling.
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Old November 6th, 2009, 13:21   #8
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Quote:
Originally Posted by aja8888
BK: I don't understand your comment. I use one quart of soy-based biodiesel (bought from Houston Biodiesel) per tank of D2. I put the quart in after the D2 fill when I get home. I buy the biodiesel in 5 gallon increments and store it in a poly container.

Am I doing something wrong or not recommended?

Thanks,

Tony

yes, Tony, you are.

Because the biodiesel has a lower density, it will have a tendency to just lay there on the top of the diesel layer and not mix properly. It would be much better if you put the biodiesel into a 5 gallon jug, filled it with diesel, mixed it up good by shaking, and put it into the tank before topping off with diesel. At the very least, put the biodiesel in first before pumping anything into the tank.

Beyond that, I see you are in Connecticut . . . biodiesel and diesel also mix very poorly when either is below 40 degrees F. You would be much better served by mixing that 5 gallon jug after storing both parts in the house for a day or two, where they will be warm, and mixing one last time, before you put it in the tank, and top off.

Last edited by naturist; November 6th, 2009 at 13:26.
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Old November 6th, 2009, 13:27   #9
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Quote:
Originally Posted by naturist
yes, Tony, you are.

Because the biodiesel has a lower density, it will have a tendency to just lay there on the top of the diesel layer and not mix properly. It would be much better if you put the biodiesel into a 5 gallon jug, filled it with diesel, mixed it up good by shaking, and put it into the tank before topping off with diesel. At the very least, put the biodiesel in first before pumping anything into the tank.
I was thinking about doing that as I have a 2 gallon fuel can available. Makes sense. I really just started this addition process to get the best lubricity I can since we have a great supply of quality biodiesel here.

Thanks,

Tony
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Old November 6th, 2009, 13:28   #10
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Quote:
Originally Posted by naturist
yes, Tony, you are.


Beyond that, I see you are in Connecticut . .
Check sig as I am a Connecticut Yankee stuck in Texas (for good, I think)!!!

We have pretty mid winters in Houston.
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Old November 6th, 2009, 14:36   #11
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I didn't even think of the two not mixing well together, but then again I would never just top off my tank with something other than what's already in the tank and expect it to mix well. Even with regular fuel additives it's recommended to put them in BEFORE filling up. Mainly I'm just trying to warn people of the potential for water dropping out which was noted and mentioned to me by a local biodiesel start-up company a few years ago. The manager warned me against splash blending in my tank and said they get noticeable water accumulation at the bottom of their storage tanks which they have to drain out.
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Old November 6th, 2009, 14:44   #12
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Quote:
Originally Posted by Diesel Addict
I can see from the postings here that a lot of people are still not aware of this. Take it as good advice. Biodiesel has higher water solubility than diesel and when the two are mixed some water may drop out of the solution. This water is normally drained from the bottom of storage tanks by professional bio producers. If you mix the two in your fuel tank, there's a good chance you'll get some water in your fuel system. If you want to use bio as a lubricity additive or whatever, buy it pre-blended straight from the pump. Don't blend it in your tank!
I have 7 years, 170K miles and four vehicles of experience with BD to contradict this statement.

Using a pump/nozzle will mix this in your tank, so not sure where you are getting this from.

Again, quality BD does not have this issue and they should be using a water filter cartridge on the BD pump to catch any moisture that may be there.
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Old November 6th, 2009, 20:43   #13
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What, don't you guys drive your cars after filling up?
No way you are going to get stratification, non-homogenous mix maybe.
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Old November 7th, 2009, 04:08   #14
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Quote:
Originally Posted by AUS_TDI
What, don't you guys drive your cars after filling up?
No way you are going to get stratification, non-homogenous mix maybe.
Of course we drive 'em. But the amount of "sloshing" around is low, unless you manage to get upside down several times. A good roll down an embankment will do the job, but just driving down the road won't. If you'd like proof of this for yourself, fill a half-liter soda bottle (glass preferred, clear, colorless, so you can SEE what happens) about 2/3 full of diesel, then add a layer of biodiesel on top. Leave some air space in it, and put it in your cup holder as you drive around. You'll find it'll just sit there on top, no matter how many weeks you drive around with it in that cup holder.
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Old November 7th, 2009, 05:13   #15
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Biodiesel / D2 blending discussion starts at slide 13 of the link below. See pics on the stratification. Note that with splash loading to make B20, there is virtually no immediate stratification but some after 24 hours. I doubt that splash loading a quart of B100 to a tank of D2 (to make about B2 for lubricity purposes) will be of any consequence especially if the car is driven daily. But draw your own conclusions. I certainly wouldn't splash blend much higher.

http://www.cdc.gov/niosh/mining/topi...b-Campbell.pdf
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