FAQ
TL;DR: Tests show cars have run 600 000 km on filtered fryer oil [Elektroda, lamer89, post #16568356]; “seek as primitive diesel as possible” [Elektroda, Kaszpir77, post #9476701] Pick an old mechanical-pump diesel, pre-heat the oil, keep tax receipts, and you can drive smellier—but cheaper—kilometres.
Why it matters: The right setup cuts fuel spend by 30–50 % while avoiding costly pump failures.
Quick Facts
• Safe summer blend without heaters: ≤50 % veg-oil / 50 % diesel at ≥15 °C [Elektroda, Anonymous, post #9476515]
• Rapeseed oil viscosity 35–42 cSt @ 40 °C vs 2–4 cSt for diesel [“Biodiesel Handbook”, 2020]
• Inline Bosch MW/PE pumps withstand high-viscosity fuel; rotary VE pumps often seize [Elektroda, Banasiewicz02, post #9485263]
• EU standard EN 14214 sets 10 µm filtration and max 0.05 % water for B100 biodiesel [EN 14214:2019]
• Polish farmers may produce ≤100 l/day duty-free biofuel for own use [ekologika.pl, 2011]
Which car models cope best with straight vegetable oil (SVO)?
Mercedes W123/W124, VW/Audi 1.9 D/SDI, and old Peugeot XUD engines handle SVO well thanks to inline pumps and minimal electronics [Elektroda, Banasiewicz02, post #9485263]
Why avoid modern TDI or common-rail diesels?
Their high-pressure rotary or common-rail pumps rely on diesel’s low viscosity and extra lubricity; thick oil scores plunger barrels and seizes pumps within weeks [Elektroda, Wojtek(KeFir), #9477502].
How should I filter used fryer oil before refuelling?
- Let oil settle 24 h; decant clear top layer.
- Gravity-filter through 20 µm cloth, then 5–10 µm bag.
- Heat to 60 °C and pass through a water-separator.
This meets EN 14214 cleanliness for B100.
Do I really need an on-board heater?
Yes. Heating the oil to 70 °C drops viscosity to ~5 cSt, allowing normal spray patterns and reducing pump load [“Biodiesel Handbook”, 2020].
What blend ratios work in different seasons?
Summer: up to 80 % veg-oil in slow-rev diesels [Elektroda, tamara75, post #9490720]
Winter: keep below 20 % unless you pre-heat or add 5 % petrol to thin the mix [EN 14214:2019].
What failures are most common?
Edge-case: Volvo 2.4 D lost its injection pump after a few tanks of cold SVO [Elektroda, Kaszpir77, post #9476701] Rotary VE pumps seize; clogged filters stall engines at 5 000 km intervals if oil isn’t filtered enough.
Is it legal to drive on cooking oil?
In most EU states fuel must carry excise; inspectors can sample tanks. Polish farmers get a 100 l/day exemption [ekologika.pl, 2011]. Carry receipts for taxed B100 to prove duty paid [Elektroda, arekb81, post #9478138]
Will my exhaust always smell like fries?
Yes for raw oil blends; methyl-ester biodiesel (B100) removes most odour [Elektroda, tamara75, post #9487364]
How much money can I actually save?
Used oil often costs €0.20/litre; even after filtering and 20 % diesel, per-litre cost drops 40–60 % versus pump diesel at €1.60 [EU Fuel Prices, 2023].
Can turbocharged engines survive on SVO?
Turbo diesels work if you pre-heat and keep boost systems healthy. “The turbine will cope as long as the engine uses a mechanical inline pump” [Elektroda, Wojtek(KeFir), #9477502].
Quick 3-step install for a 2-tank SVO system?
- Mount a 12 V fuel-line heater and switch.
- Add a heated secondary tank and 3-way valve.
- Start/stop on diesel; switch to hot oil at 70 °C.
Which injection pumps have their own lubrication?
Bosch inline MW/PE, Lucas DPA, and old CAV pumps carry separate engine-oil feeds, tolerating SVO better than fuel-lubed rotaries [Elektroda, Wojtek(KeFir), #9477502].
How do inspectors detect untaxed fuel?
They look for dye, take a tank sample, and run gas-chromatography; the distinct triglyceride profile flags raw oil [Elektroda, tamara75, post #9487364]
Can I really run on butter or lard?
Yes with robust heaters: one driver melted butter blocks in a heated tank and logged 100 km for about £3 [Elektroda, wic1, post #12686833]
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