Check each biodiesel batch for clarity, a golden amber colour, thinness compared with the original oil, a clean burn and a pass on the 3/27 test with methanol, and keep a record of the batch. These field tests are screens, not a guarantee: none of them finds residual methanol, partly converted oil or soap reliably, so run a new fuel at 10-20% in an engine first and watch the filters.
Part of Biodiesel Production
Quality testing for biodiesel is the set of simple checks that show whether a batch has converted, washed and dried properly before it goes in an engine.
What Each Check Tells You
The parent lists these tests for a finished batch:
| Check | Pass | What it catches | What it misses |
|---|---|---|---|
| Clarity | clear, no haze | water (haze = water) | dissolved water, soap |
| Colour | golden amber (vegetable), pale yellow (tallow) | little | most things |
| Thinness | much thinner than the original oil | unconverted oil | partly converted oil |
| Lamp burn | clean bright flame, little smoke | gross failure | methanol, glycerides |
| 3/27 test | 3 mL of fuel dissolves in 27 mL of methanol | unconverted oil | partial glycerides (27 Conversion Test) |
Details are on Clarity & Water Content and Cold Weather Performance.
What Bad Fuel Does
Reasoning from what remains in a poor batch, not from a sourced standard: leftover methanol lowers the fuel’s flash point, making the stored fuel a fire hazard and attacking rubber parts; leftover soap and glycerin clog filters and coke injectors; unconverted oil thickens the fuel and leaves deposits; water feeds microbial sludge at the fuel-water boundary (Diesel & Heating Oil). All of these show up first as blocked filters.
What You Need
- A clear glass jar, a thermometer, a pH strip for the wash water
- A small amount of methanol for the 3/27 test, under the same precautions as production
- A lamp that burns the fuel (Oil Lamp Construction)
- A batch log, as the parent’s record-keeping list: date, oil source, titration result, lye amount, methanol amount, temperature and time, separation quality, number of washes, test results and yield
Method: Introduce A New Batch Slowly
Step 1: Run the tests above. Reject cloudy, thick or dark-layered fuel for re-processing or disposal.
Step 2: Settle the passed batch for a few days and decant it off any bottom layer.
Step 3: Blend it 10-20% in the engine’s usual diesel (a conservative start; the parent mentions B50 for cold weather but gives no first-use ratio) and run the engine for a day.
Step 4: Check the fuel filter. If it clogs, stop and look at the batch. If clean, raise the proportion gradually.
Common Mistakes
- Trusting the lamp. A fuel that burns can still wreck an injector.
- Skipping the log. The batch record is how you learn why a bad batch happened.
- Putting an unwashed batch in a tank. Residual lye and soap damage fuel systems.
- Using the fuel in rubber lines. Old rubber hoses and seals may swell or crack; the parent allows for fuel-line material changes.
Methanol in the test and in the fuel
The 3/27 test uses 27 mL of methanol that is poisonous, flammable and absorbed through skin; do it outdoors with gloves and goggles and treat the leftover mixture as hazardous. Unwashed fuel can hold enough methanol to ignite at a low temperature; keep fuel away from flame until it has passed washing and drying (Methanol Hazards).
What’s Next
- Learn next: 27 Conversion Test, for the conversion check
- Combine with: Cold Weather Performance, since a good batch can still gel in winter