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Wednesday, November 14, 2012

Lets Talk Biodiesel

I thought I’d do a thumbnail sketch on Biodiesel, so that diesel engine owners are made aware of the potential problems that can arise from its use.  This won’t be a scientific, in depth study, but just a simple look in layman’s terms that I hope you can understand.

Thanks to our national policy of trying to reduce the importation of foreign sources of oil, movements to increase the use of renewable fuels, such as ethanol and biodiesel mixtures added to gasoline and diesel fuel, respectively, has taken place all across the country.

Biodiesel is most often made from soybean oil and/or rapeseed oil and mixed in with the refined diesel made from crude oil.  It can be made from animal fat based oil (like used french fry oil) but that is very rarely sold commercially.

Biodiesel, when compared to straight diesel fuel can reduce energy efficiency from 5 to 7 percent, causing fuel mileage to drop and may cause a noticeable reduction in engine power.  Plus it can attract moisture in greater volume, doing two things, contaminating the diesel fuel and creating a more favorable environment for the growth of bacteria (or more commonly called algae) in the fuel tank.

Serious fuel contamination can lead to plugged fuel filters causing engine power loss, or missing.  It also can lead to damage to very (very) expensive fuel pumps and injectors.  This kind of damage is often not warrantied by engine manufacturers or extended warranty policies.

I’ve noticed more and more diesel fuel pumps are now sporting stickers saying that the fuel contains biodiesel in percentages from 5 to 20 percent.  You don’t know how much biodiesel is actually in the fuel you are putting in your tank.

Biodiesel, with its propensity to draw in water moisture can cause problems for motorhomes in storage, especially in warmer temperatures.  That again can cause an environment for bacterial growth.

What can an owner of a diesel engined motorhome (or truck) do to mitigate the potential problems caused by biodiesel?  Several steps can be taken.

First, consult your engine owners manual to see what percentage of biodiesel is acceptable.  For my CAT C-7 diesel engine, I’m not to use biodiesel in amounts greater than 5 percent.  I no longer will fill my tank at any pump that has that sticker on it saying “Contains Biodiesel in amounts between 5 and 20 percent”.  I’ll move on to another fuel station.

I also try to fuel up when I’m at one half of a tank.  That way if I’m caught in a situation where I’m forced to use diesel fuel with a higher percentage of biodiesel, it will be diluted by the fuel already in the tank.

I recommend the use of a diesel fuel additive (there are many out there for you to choose from) to offset the biodiesel.  The additives can help to emulsify the biodiesel so it is spread more evenly into the diesel fuel. In some cases, the biodiesel does not mix evenly in the diesel fuel and can “clump” together.  The additives can also keep the fuel pump and injectors clean as well as inhibit bacterial growth.

Keep an eye on your fuel filter/water separator and drain off any water that may be found in the drain bowl. 

I recommend if you need to store your motorhome for an extended period of time, fill the tank as full as you can get it and add a fuel additive.  Marine stores usually have a good selection of additives because boats often spend a lot of time in storage.

Lastly, carry at least one set of fuel filters (I carry two).  That way, if your filters get plugged, you can change them (or have them changed) and be on your way.  Make sure to have your fuel filter(s) changed according to the manufacture’s recommended intervals.

Biodiesel (and ethanol) is here to stay, we have no choice and will have to learn to live with it.  These few simple steps hopefully will keep you rolling down the road and continue to enjoy your travels.

Thanks for visiting and feel free to leave a comment.



  1. Thanks for the thumbnail explanation; based on your post in the past days, Mui's checked the specs for our engine. We also fill up when we're at about half tank and always try to keep a full tank when we're not on the road ... all good things.

  2. When I drove my big truck I always carried spare fuel filters. I also found a shot of Power Service once a month kept the water in the fuel problems down.

  3. Mercedes also says no more than B5 and states avoid any bio fuel if at all possible. Good summary of the problem.

  4. Huh? You said "let's talk Biodiesel" and you really want ME to talk biodiesel with you? I don't think so.

  5. At least that's one thing us gas guzzlers don't have to worry about. But there's always ethenol.

  6. Thank you so much for all your posts rv maintenance.

    We wondered about the bio-diesel. We stopped at a Flying J (the Rv side) once where that was all they had. We didn't know what to do and asked the guy ahead of us. He had an almost empty tank and said he had used it before with no problems. We took a chance and topped our tank off, but I think it was only 25-30 gallons. We had no problems, but I wonder about the guy that filled his tank ahead of us. Now, we always go over to the truckers side of Flying J and so far have been able to avoid bio-diesel.

    We'll definitely follow your advice and keep two sets of fuel filters on hand..just in case.

    Thanks again for the tips....keep em coming!

  7. Thanks for the explanation and info on bio-diesel. I started noticing those 5% bio-diesel signs at the pump just a year or so ago and have been trying to avoid them like the plague. But, as you say, it's getting harder and harder. I think I'll look into an additive - after I talk to Mr. Goodwrench!!

  8. Thanks for the information! Since we are just a week in to owning our diesel, we have a LOT to learn!

  9. We have considered running with a half tank of fuel to help our mileage. Now I am wondering if that is a good thing. Any opinion?

    1. I don't find much diffence in mileage with full tank vs half tank. Remember your generator won't run if fuel gets below 1/4 tank. Plus you may be forced to buy fuel where you have no choice because you are too low to go anywhere else.

      I always have plan "B" and try to always fuel at not less than 1/2 tank. I want to have plenty of fuel for my genny in case I'm sitting on the side of the road with a mechanical problem or flat tire in 100 degree temps.

      You are right that fuel adds weight, but if you travel with 1/2 tank of water and empty holding tanks that would help. :c)

  10. One important benefit of filling up when you are only half empty that you forgot to mention is the reduced risk of a cardiac event curtailing your travel.

  11. I admit it - we don't have a diesel so I didn't even read your post. I'm sure it was very interesting, though.