My (new to me& first diesel) '05 Dodge 3500 5.9l diesel truck

I have 2 questions.

1. I’m getting really good mileage and someone said it must have a “chip” in it. What is a chip and where is it at, and does it ever need maintenance?

2. I’ve been told that I can put pure vegetable oil in my truck instead of diesel by someone, then I’ve heard don’t do it that it’ll ruin the engine, and then someone else told me not to run any sort of biodiesel in it without a conversion kit. What’s the real truth of the matter?

I don’t know a lot about diesels, but I’ll give it what I’ve got.

  1. The chip they are referring to is in the PCM (powertrain control module a.k.a. “the computer”), replacing the original one. Generally, these chips improve power, not fuel economy (how do you define “really good mileage”?). No maintenance required. Often, the “chip” is actually a reflash of the original PCM programming, with no actual hardware change.

  2. Running straight vegetable oil in a totally stock vehicle is usually not possible without driveability problems (especially in cold weather) and I believe the fuel system can be damaged.

There are a few diesel mavens here, so I’m sure one or more of them will fill in the blanks and correct any errors in what I’ve said.

Congratulations, you’ve got the best small truck diesel on the market. The Cummins is top of the heap, superior to the Navistar in the Fords and the Isuzu in the Chevys.

The “Chip” you are referring to is really a misnomer. It used to be that you replaced the original PCM chip with a different chip. These days it’s a program that gets flashed into the PCM. Some of the diesels have a module on them that allows you to have 3 power levels. If you don’t see a funny box around that says Bullydog or something similar on it with a knob or buttons, chances are, it’s a flash.

That said, that engine naturally gets good mileage for that size truck. 20 mpg is about normal empty for an 05.

No, you can’t run pure vegetable oil instead of diesel. You can turn oil into fuel but it has to be processed removing the parafin and contaminants in it or you’ll screw up the works. You can probably safely run 20% biodiesel, more than that is asking for problems.

In the winter bio diesel mixes cause problems because bio diesel, oil mixes gel at a lower temperature and require a tank heater to keep it from gelling.


How good of MPG’s are you getting??? Like NYBo said, the chip like you are thinking is more directed at power than fuel economy. I have a Ram 3500 Diesel of my own. I have a friend who works for Cummins south and is a diesel expert, he services my diesel. He did some tweaking on my injector pump which gave me better MPG’s (I went from about 15 to 22 MPG’s). This guy also runs WVO Biodiesel in his truck (A Ram dually) He runs 60% Biodiesel and 40% regular diesel with no kind of conversion kit at all. I did some research myself on Biodiesel and have even ordered a Biodiesel processor to make my own. You CAN concievably run 100% Biodiesel with no kind of conversion but again like NYBo said its not too friendly in the colder weather. Check out this site. Biodiesel gels at higher ambient temps than regular Diesel. Most people run a 20% Biodiesel to 80% Diesel combination. It is recommended that when running Biodiesel in an older engine that you change your fuel filters every 1000 miles for the first 3000 miles due to the fact that Biodiesel will clean your fuel system and will dislodge deposits in the fuel system. I should have my processor in a few weeks and will let you know how it works for me.
There was a show called “Trucks” where the host made his own Biodiesel on the show, he showed how easy it is to use a processor and in the end, he filled his Ram with 100% Biodiesel and drove it smoking the tires.


Straight vegetable oil is not the same thing as biodiesel, but I don’t know what needs to be done to convert it. Skipper, transman, Craig58, what’s the scoop?

Vegetable oil won’t ruin the engine. But it will cause damage to the fuel system if used over time. Vegetable oil contains amino acids. And over time, these acids corrode the fuel system causing damage to expensive components.

Stick with diesel fuel.


By mixing Methanol and Lye with the filtered and washed WVO to control the PH, you can make Biodiesel. Check this site out Click on their FAQ tab. These two web sites is where I got most of my info from.


You mix methanol and lye in the processor to control the PH. click on FAQ.

They advise if you keep your fuel system serviced (Change filter every 1000 miles for the first 3000 miles then every 15k) you will be ok. These two sites I listed is where I got most of my info. It would be interesting to hear from anyone who has used the stuff.


Straight vegetable oil is a mixture of molecules with different weights and properties. Vegetable oil can be used, but the glycerin needs to be removed first. That is the paraffin Skipper referred to. Paraffin is wax and you don’t want that to gum up your fuel delivery system. You cold remove it by chemical reaction, but you probably don’t want to do that unless you have cheap surplus fryer oil available. It is a time consuming process and it isn’t free.

He asked about vegetable oil. Not bio-diesel. So I answered what can happen when regular vegetable oil is used.


Vegetable oil and used fry oil are the same thing, only one is dirty and contaminated by whatever they fried in it…By the time you filter it and separate out the glycerin, (with lye) you lose about 1/3 of your product…And now you must find a place to dispose of that stuff…Most bio-diesel conversions include a tank and line heater to prevent viscosity problems, or at least minimize them…The whole process is explained in great detail on several web-sites. Google will take you there…

I looked into it once. It seems like they said it took about 5 days to produce a batch of fuel from fryer oil. I need about 40 gallons a week so I’d need to process about 50 or 60 gallons of french fry juice to get it. That would mean I’d have to dig around to 4 or 5 greasy spoons a week to collect oil. IMO, it’d be like having a milk cow in the back yard to get a couple gallons of milk a week. Not really worth the effort, leave it to the people with the facilities to milk the cow and convert the oil. On the other hand, if you had a facility large enough and trucks to haul the oil in and refine it in quantity, maybe it’d work out.

My Dodge says in the book to not use more than 20% bio diesel in it. I’ll never have that problem because it’s not sold around here, but that’s where my figure came from. Honestly, if it has a chance of screwing up a $12,000 engine or a $4000 injector pump, I ain’t using it.


Others have adequately described the “chip.”

Let me just say that biodiesel is a poorly define term at present. Some people mean waste vegetable oil that has been processed, some mean unused vegetable oil that is processed and added to regular diesel. If you are buying at a commercial biodiesel pump it is the latter and they have classes from B5 to B100 representing what percentage is bio sourced. My understanding is that pretty much any standard diesel can run on B5, B10, and B20. Maybe higher, but the manufacturers are being cautious and won’t cover warranty if you use higher percentages.

The straight vegetable oil and/or waste vegetable oil is generally back yard hobbyist stuff at this point. I would stay away from those unless you are willing to risk your expensive new diesel engine and its fuel system for an experiment.

Here is a link to some information about commercial biodiesel:

MPG’s…my truck is a 4 door, single axle, long bed 3500 and when empty on longer hwy trips (no stop and go) my best mileage was 26.7mpg. Usually, when going to and from work (21 miles round trip & with a little bit of highway speed, but mostly in town) I’m getting 22mpg. I can almost go a month on one fill, provided I don’t do a lot of running around in town. When towing my 5th wheel and going the speed limit, I getting 14.5 mpg.