Water in Diesel fuel

[whizznbyu]

Why is there water in diesel fuel? Is it a condensation problem? Or rain that finds its way into the holding tanks at stations? Would using diesel additives such as Diesel Kleen really help? 2005 B5 and 2009 Q7 TDI.
Thank you.

 

[n1das]

Why is there water in diesel fuel? Is it a condensation problem? Or rain that finds its way into the holding tanks at stations? Would using diesel additives such as Diesel Kleen really help? 2005 B5 and 2009 Q7 TDI.
Thank you.

PowerService Diesel Kleen is good stuff but it doesn't do anything for water. Use the PowerService Diesel Fuel Supplement (white bottle) stuff instead.

Water in Diesel fuel? YES! Always. More so in winter compared to summer. Even with the driest diesel fuel available, there is always a small amount of dissolved water present. The dissolved water normally isn't a concern. It's slugs of free water that have dropped out of suspension that you need to worry about. It only takes a single tank of water-contaminated fuel to do a lot of damage to an expensive injection system.

Diesel fuel is hygroscopic, meaning that it holds onto water and soaks it up like a sponge. It willl soak up water over time. It's worth it to regularly use an additive that increases lubricity and does something for water.

To make sure you're getting only the freshest and driest fuel in your area, stick to fueling up only at truck stops and high volume gas stations along major routes. Go where the big rigs go. Basically buy your fuel where everybody else does in your area. This is particularly important during the winter months. The fuel will always be the freshest and driest at these stations because it's constantly being replaced often. Avoid fueling up at stations that rarely get any diesel business, no matter how tempting the slightly lower price per gallon may be. Over time and through experience you'll learn which of your favorite high turnover stations have the best quality fuel and then stick to fueling up only at those stations.

I've been following the simple rule above since day one with my 02 golf TDI. After "only" 354k miles, it is still on it's original injector pump with no issues.

Good luck.

 

[RalphVa]

I had 32 years of driving a 220D and then a 240D, we have never ever experienced a water problem. I agree with the previous poster's recommendation to use PS, but we also never used an addition in 32 years of driving. I do disagree that diesel is hydroscopic. It is not. It may be slow to release water if it gets in beyond the solubility limit, but it isn't hydroscopic.

One thing recently that I ran into with my tractor is wax in the diesel. First I thought it was water and even changed out some fuel that I'd just bought. Found 2 globs of whitish/yellowish wax near the outlet from the tank. On this forum, someone posted a company's finding that wax will drop out of ULSD at temperatures below 10 F. This happened to my tractor. An additive tailored for ULSD will help to keep this from happening. So, I'm still thinking whether to use an additive in our 2010 Jetta TDI. It's kep in a garage that rarely gets below about 40 F, not conducive to wax formation.

 

[n1das]

but it isn't hydroscopic.

Technically, you are correct. It isn't hyDroscopic. It is hyGroscopic.

http://www.intellidog.com/dieselmann/b_smoke12.htm
http://www.dieselfits.com/Purging-Fuel-Systems/purging.html
http://www.biodiesel.org/pdf_files/Changes_in_Diesel_Fuel.pdf

 

[RalphVa]

I meant hygroscopic. It isn't.

Hygroscopic has the property that it likes water. The water becomes attached to it by electromotive (or similar; forget what it's called exactly) or bonding. THIS is called hygroscopic. Propane is somewhat like this, as it forms a hydrate. Diesel, to my knowledge, does not hydrate.

Brake fluid is hygroscopic. Diesel is not.

 

[ProfBooty]

One thing recently that I ran into with my tractor is wax in the diesel.

As I understand it, wax (paraffin) is pretty much the primary ingredient in #2 diesel and responsible for the additional BTU content. It's what makes the fuel gel in the cold.

 

[RalphVa]

Paraffin cannot be much of what's in diesel. Otherwise, we'd have a terrible gelling problem. It may be 5 or 10% of it. If there's very much, the diesel has to go through a dewaxing process. This is usually a catalytic one whereby the wax is absorbed onto a catalyst and then chopped up into lighter fuel that is distilled off. There is a catalytic process that would add side chains to the paraffin or wax. This converts it into good, low pour point diesel. Doubt very many refineries have this process. Exxon use it to make "synthetic" lube from wax in their Baytown refinery. I suspect that this is what Castrol are buying and calling "synthetic" lube (I don't know, because this Exxon plant was started up after I retired, but Castrol was buying pretty much all their lubes from Exxon).

 

[ProfBooty]

According to this http://en.wikipedia.org/wiki/Diesel_fuel diesel is about 75% saturated hydrocarbons which it states is mostly paraffins. But, following the link on what a paraffin is, it isn't strictly wax. Some are regular liquids and apparently even methane is considered a paraffin. That would make sense then that there probably isn't that much 'wax' per se but still a lot of paraffin content.

 

[Powder Hound]

Paraffin = wax. It is strictly, by definition, wax. What is hard to wrap your mind around is that you didn't think about the fact that there's different types of wax. Some of them are solid at standard temperature and pressure. Others are liquid, and still others are gaseous at STP.

 

[mrGutWrench]

I meant hygroscopic. It isn't. (snip)

__. True. Diesel fuel is not hygroscopic in a chemical sense but physically, it loves to dissolve water and hold it in that dissolved (or suspended) form so long as the amount is limited. As N1 says, the biggest problems seem to come when the water "clumps" and drops out of the dissolved/suspended state. I guess it's kind of an "oil and water" doesn't mix but the water molecules will "hide" between the molecules of fuel.

__. I don't know if the water comes from molecules in humid air or if the humid vapor condenses and then gets taken up by the fuel. But if you have diesel fuel (at least any that's not been handled in laboratory conditions), it will have a certain amount of water in it.

 

[Rod Bearing]

In the days of old, before common rail systems, emulsified water in small amounts was always preferred to larger amounts of free water in the system.

Now, with pressures in the 25,000 psi range, emulsified water is death to a HPFP and the multi cycle injection systems.

Emulsified water in a common rail system causes a phenomena not that unlike cylinder wall cavitation. Only it happens in the HPFP and high pressure components of the injection system.

A good water separation system combined with a lubricity and demulsify treatment in the tank nets the best results.

The problem is, most of our diesel now has 5 or more percent of bio diesel added to the ULSD which makes it inherently prone to having water in it.

You get lubricity gains with bio while at the same time, it has water emulsified in it.