As you all know, I’ve been working on my truck to beat the coking issues that present themselves while burning waste oil. I recently posted a video after pulling the injectors to show what my precups looked like. What I found was that the oil had not sufficiently burned and had completely filled the precups with solid carbon deposits. In most cases, the carbon even covered the tips of the injectors, only leaving a pinhole for the needle. This issue led to very poor combustion of even standard diesel fuels and resulted in smoking in most scenarios and very poor fuel efficiency. All of this is somewhat typical of coking.

As I stumbled through the process of pulling my injectors, disassembling, cleaning, rebuilding, and installing them, I tried my best to record the process so I could share it. The result was this:

Ok, so I’ve just removed my injectors and I may be in for more than I bargained for. I’ve got rust, dirt and coking to battle and I’m not sure how to deal with it. It seems that the coking didn’t infect my injectors at all, rather, it all stayed in the pre-cups and combustion chamber. The worst I had to deal with on the injectors was some rusty threads. At first, I thought this was great. My injectors looked good and really didn’t need much more than pop testing and some shims.

The injector holes in the head are a completely different story, though. I’m really not sure how to deal with it. They are full of rust, carbon and plugged with coking. It seems like mist of it will scrape off which is a good thing, but the part that really worries me is what I can’t see.

Check out the video I made with an endoscope. It may not be a good idea to watch full screen if you get motion sickness, so bear with me.

As you can see, they look pretty nasty. What gets me the most, though, is seeing how the coking built up around the injector tip. I don’t understand how it doesn’t seem to have really affected the injectors. I had assumed that the coking issue would be limited to buildup around the tip of the injector similar to this picture:

Coking on tip of injector

Coking on tip of injector

As for now, I will be brainstorming ways to remedy this while I rebuild my injectors. Any suggestions for cleaning, sans pulling the head, would be greatly appreciated. More updates will come as I progress through this.

Last weekend, I decided to replace my glow plugs. Although incredibly reliable, I find the 7.3L IDI to have an incredibly finicky glow plug system; even with the solid state controller. I decided to bypass the controller to go with a momentary push button for increased reliability and this is what I found:

The orange ones are bad

The orange ones are bad.

Old glow plugs 8k miles.

Old glow plugs 8k miles.
















Is it good, bad, neither? I don’t know. Generally, the black seemed to just be soot that would easily wipe away. However, there was evidence of some coking and the tips of a couple glow plugs had swelled. It seems that the bad plugs had the most buildup.

Something all waste oil burners need to be aware of is coking. Unwanted harmful buildup of unburnt fuel and dried hot oil. It can kill your turbo, performance, coat your pistons, and limit your injectors. If you notice more smoke, white at idle or black at throttle, less power, or hard starting, you may have coking issues.

One of the inherent problems with WMO and other waste oils is that they usually have a high flash point and a high auto ignition temperature. As a reference point, diesel has a flash point of 144*F and an auto ignition temp of 410*F. Likewise, RUG has a flash point and an autoignition temperature of -6*F and 480*F respectively. Most of the waste oils that I currently use have a flash point of around 400*F, however, since they are not intended for use as fuels, they do not list autoignition temperatures, but from some safety bulletins it seems like they are in the 500-750*F range.

Autoignition- Minimum temperature at which the fuel vapor will spontaneously combust without other external ignition sources.

Flash Point- Minimum temperature at which an external ignition source will cause the fuel vapor to combust. It is important for a diesel to have a high flash point and a low autoignition temperature. Our numbers are not too far off and it seems that adding RUG may actually help bring the autoignition temperatures of our blends down a little, although it hurts by bringing down the flash point as well.


I’m still working on a solution to coking, and although I may never find it, I do believe that it can be mitigated. Sometime in the near future, I plan to pull my injectors to inspect and clean them. My hope is that the tips are easily cleaned and that the pintles are not ruined.

This game we all play is a guessing game sometimes at best, and sometimes I am clueless, WMO for fuel that is. I have had batches that ran better than diesel, I have had batches that run worse than diesel. I have batches that ran good, but got progressively worse.

A lot of the times I was guessing at what my problem was. Sometimes after making changes and placing blame I found the real problem by accident.

I have jumped around from running almost no oil to running pure oil back to half back to full back to none. All was done trying to figure out what a problem was.

I have changed my percentages, changed my blend from gasoline to D2.
I have plugged filters, and I have had months of no problems. I have had weeks where I had nothing but problems non stop. I have had days reveling in how little a trip somewhere was costing due to running my own fuel.

What have I found? The two most important things;

1: DRY YOUR FUEL do everything in your ability to make sure your batch is dry. I learned by accidentally leaving 10,000W of heat on for a few hours that dry fuel runs better, and even when I thought it was dry, I have been proven wrong every time by the boiling test. I now put 5500W of heat in a batch for several hours. I watch it periodically and once it starts boiling, I allow it to boil until it stops, and then I continue heating until the oil is giving off a tiny bit of smoke. At my electricity cost, heating for 8 hours ~ 8 bucks. Cheap insurance, one water blocked filter cost 10 to 30 bucks depending on the type.

2: CLEAN YOUR FUEL I have had more trouble than anything else, from assuming a batch was clean because the fuges ran for 6 to 8 rs. Install finishing filters on your equipment with a rating BETTER than your under the hood filters. I learned that lesson the hard way. I made two mistakes on a batch I made back in the summer. I assumed it was wet, and it was not. I assumed it was clean, and it was not. This caused me to spend an entire week changing filters on the mail rt, and on the side of the rd in both my car and in my wife’s car. During that week I made three mistakes, two of which I mentioned above, and the third was not knowing what the micron rating was on the under hood filters for the Mercedes. If I had known that my under hood filters were 6 micron filters I would have evaluated things differently.

Have a safety system on your equipment. There is nothing like having to clean up an entire drums worth of fuel from concrete and gravel. I am planning on having my next system encased inside of a 275 GAL tote that has had it’s top cut out, OR building a large plywood tank around the processor and gluing and painting it to make it into a “tank” to catch spills.

Take real notes, add things like temperature, mix, wmo source, running conditions, filter age, processing time, heating time, etc. One of my biggest problems is my memory bites, and I often forget to do something, or forgot the circumstances surroundiung a failure event so I suffer the same event again before I figure it out. I changed 120 bucks worth of filters on the mail rt, and on the roadside before I learned two things.
One my finishing filters were not good enough, and two don’t assume a batch is clean because of processing time.

Settle, and only pull from the bottom to transfer and settle again. Never pull from the bottom for a batch you plan on running. I have some oil in the tanks right now that has settle since past spring, and it was the easiest to clean. (I now use the centrfuges, and not time to tell me if a batch is clean)

There, ther’s my two cents worth to anyone who wants to read it.

Those pabiodiesel fuges are great for what they do and what they cost, but in my honest opinion, they suck for doing a dependable job at what we need them to do without a lot of babysitting and clean outs.

Written By: Josh Carmack of

It’s been a while since I’ve updated my site, but I wanted to share my new YouTube channel and WMO playlist. This is where I will be subscribing to videos that I like as well as posting some of my own. There are tons of videos out there on how this stuff works and wealth’s of knowledge. As you may know, with every good video there are 2-3 bad ones. I will do my best to only share ones that I believe demonstrate the best practices.


Please feel free to subscribe/follow me on YouTube and here, at All Black Diesel. Also, if you have a good video of your setup, share it here or send me a link so I can put up here on the site.

They are the cornerstone of anything performance. Without filters, our fuel systems and engines alike would quickly deteriorate. As a home-based fuel producer, I want to be sure that what I am putting in my vehicle is as clean and pure as I can make it. What’s the big fuss? A filter is as good as it says right on the box, right? Prepare to learn everything you didn’t know about filters!


Filter ratings are often misunderstood. There are a few factors for deciding which filter to choose, some of which can be controlled and others that can’t. I have tried to find as much pertinent information on filters as I could and include it here, in one place.


  • Beta ratio and efficiency
  • Filter media
  • Build quality
  • Dirt holding capacity


  • Operational conditions
  • Environmental conditions


Filter Ratings:

To begin with, there are a few different ways that filter manufacturers rate their filters for efficiency.

  • Nominal ratings:

The nominal rating of a filter refers to its ability to remove a nominated minimum percentage by weight of solid particles greater than a given size (in micrometers or microns, µm). An example of this would be 98% of 20 microns. However, I believe a more common definition of nominally rated filters would be 50% of the nominal rating for particles of the given rating or larger. I have read that some tests show particles up to 200 microns pass through nominally rated 10 micron filters. Maybe a more exaggerated example would be better. A screen door will collect 10 micron particles, so it can be rated nominally as such. However, the screen door only captures 5% of particles 10 microns or smaller.

  • Absolute Ratings:

These are probably the better rating of choice when looking at buying filters. An absolute rating means that the filter is 98.7% or better at removing particles of a given size under laboratory conditions. It gives an accurate description of the largest size of particle that will pass through the filter media. These filters are usually much more expensive. Considered a better way to represent the effectiveness of a filter.

  • Mean ratings:

This is another rating that a few filters use in the industry, although not particularly popular. It uses a rating to show the filter is effective above a certain particle size. It seems to be a better representation than nominal ratings.

Beta Testing and Efficiency:

Beta ratings are the most commonly used ratings in the industry. They are derived from the multi-pass test methods for filter elements in ISO 16889:1999.The purpose of the multi-pass test is to provide a lab based procedure which will give reproducible data. The data can be used to interpret dirt-holding capability and contaminate particle efficiency of filter elements (beta ratio).

The multi-pass test begins by mixing a known amount (mass) of particles of known size into a hydraulic reservoir. The contaminated test fluid is pumped through the filter at a continuous and constant flow rate. During this test the differential pressure (difference between before and after filter pressure), upstream and downstream particle counts and amount of contaminate in the system are continually monitored. The test concludes when the differential pressures reach a specified limit or beta ratios (particle counts) no longer become acceptable. The test specifies that it is applicable to filters with an average beta ratio of 75 or greater. Each test is divided into ten smaller time frames. Particle counts are conducted during each time frame.


Using the particle counts from the time frames, one can calculate an average beta-ratio and a single beta ratio for the entire test. A beta value is calculated by counting the number particles upstream of the filter (size times microns and larger) and dividing that number by the amount of particles downstream (size x and larger). Calculating average beta ratios for each of the ten time period (sum particle counts and averaged for each period) and graphing them against differential pressure for each time frame allows for the beta ratio to be determined for different differential pressures. A single beta value for the entire length of the test can be determined by summing the average particle counts from each timeframe of upstream particle and dividing that by the sum of the average of the downstream particles. This is the value used to determine which particle size to rate the filter at. Each beta ratio particle count is done for one specific particle size.

Using the single beta ratios filter element percent efficiency for a given particle size can be determined. The math is:


There are standard whole number beta ratios which correspond to a specific percent efficiency.


While beta testing may look great on paper and may be reproducible in a lab, it does not take into account certain realities. Beta ratios do not account for operational conditions such as surges in flow or extreme temperatures nor does it account for stability over time. Depending on how the filter media is tested, it may not take into account build characteristics or flaws either.

Filter Media:

Dirt holding capacity is another crucial factor determined in the ISO 16889 multi-pass test. The dirt-holding capacity is how well a filter can retain particles once they have entered the filter media. This may be the most crucial factor in a filter. There are two main styles or filters: surface (membrane) and depth (bypass) filters.

Surface filters trap dirt on the surface and depth filters allow the oil to flow throughout the body of the filter and trap particles within the media.


In addition, both depth and surface filters have the following filtration properties:

  • Entrapment: Particles collect on the media due to pore size being smaller than the particle.
  • Adsorption: Natural electrostatic attraction between particles and media.
  • Impact: Particles impact media and become stuck due to adsorption.
  • Brownian Movement: This is less common, but it pertains to small particles suspended in a fluid having random movement in regards to flow.
  • Gravity: The natural force which helps larger particles settle out of oil.

Each filter has media with a specific pore size. As the pore size decreases, differential pressure increases. To compensate, the number of pores per unit of area must increase (porosity or pore density). Without enough porosity and too much differential pressure, a filter may bypass or fail.

Filter media is most commonly made of two different types of materials:

  • Cellulose: Generally a wood pulp material with inconsistent pore size and larger fibers. This material tends to have less holding capability than a synthetic material and tends to fail quicker in high acid and temperature environments.
  • Synthetic: Generally made of a fiber-glass style material. Has a very consistent pore size. Due to the fibers being much smaller, synthetic media has a much larger pore density and therefore a larger dirt-holding capacity. These filters are very durable and will withstand harsh environments.


 Filter Build Quality:

Last but not least, and certainly not to be forgotten, is the build quality. In the end, it really all boils down to this. You can make the best filter media, have the best advertising, and have the prettiest box. However, if you cut corners in the manufacturing process it’s all for naught. Russ Kinze performed an outstanding qualitative analysis on engine oil filters. It provides some pertinent information that would be difficult to replicate and some of the brand specific information carries over into hydraulic and fuel filters as well.

Engine Oil Filter Study

burst filter

Sweet! You know everything I know about filters. Now it all makes sense and you can go buy your buy your filters as an educated consumer…


Hey guys, I finally got the Dropbox thing going. I uploaded all of my PDF files on there to a folder called WMO. There are not a lot of files, but they have some very good information in them. Feel free to download them. If you would like to return the favor and share any files you have that I can add to my folder, that would be awesome!

Here it is: WMO Dropbox