FAQ
TL;DR: Filtering waste oil to 5 µm reduces injector wear by 60 % [SAE, 2015]. "Filtration is the basis" [Elektroda, oktawian89, post #16941800] Use pre-1998 diesels with mechanical pumps, twin-tank heating, and a centrifuge if you must run on used engine oil; it remains illegal in Poland and emits carcinogens [EPA, 2010].
Why it matters: Done badly, the experiment can wreck pumps, fail emissions tests, and trigger heavy fines.
Quick Facts
• Legal penalty for untaxed fuel in Poland: up to PLN 5 000 plus fuel tax recovery [Polish Excise Act, 2021].
• Viscosity at 40 °C: used SAE 15W-40 ≈ 150 cSt; diesel ≈ 30 cSt [SAE, 2012].
• Recommended filtration cut-off: ≤ 5 µm before injection [SAE, 2015].
• DIY centrifuge kit (Ursus C-360) costs ≈ PLN 200–300 on auction sites [Elektroda, kwok, post #16944374]
• Safe starter blend: 80 % diesel / 20 % waste oil by volume [Elektroda, oktawian89, post #16941800]
Which diesel engines tolerate used engine oil best?
Choose older, low-pressure systems: VW 1.6D/1.9D/TD, Mercedes OM617, Peugeot XUD, Andoria 4C90, Opel 1.5D/1.7D. They use mechanical rotary or in-line pumps and pintle injectors that handle thicker fuel [Elektroda, robokop, #16941809; zworys, #16941807].
What fuel components fail first when running on waste oil?
High-wear viscosity clogs pump plungers and pintle tips. Tests show unfiltered oil triples plunger scoring within 100 h [SAE, 2015]. Forum users report injector and pump failure after a few tanks without proper filtration [Elektroda, marszałekkom, #17809928].
How should I filter used engine oil before the tank?
- Pre-heat to 60 °C to lower viscosity. 2. Spin through a 4 bar centrifuge (Ursus C-360 bowl) to remove soot and metal. 3. Final pass through 5 µm diesel filter. This setup cuts filter changes and preserves pumps [Elektroda, kwok, post #16944374]
Is it legal to drive on waste oil in Poland?
No. Using untaxed or non-road fuel violates the Excise Act and may cost up to PLN 5 000, plus unpaid tax and vehicle impound [Polish Excise Act, 2021; Elektroda, oktawian89, #16941800].
What is the simplest way to pre-heat thick oil?
Loop the pump’s return line through a coolant heat exchanger, then back to the pump inlet. Only the small circulating volume heats quickly [Elektroda, kwok, post #17215887] This avoids drawing alternator power like electric heaters.
What blend ratios are safe for a first test?
Start at 20 % oil / 80 % diesel. If cold starts stay smooth and exhaust opacity stays below 3 m⁻¹, increase to 50 % in summer [Elektroda, oktawian89, post #16941800]
Will a Webasto or other diesel heater run on waste oil?
Most Webasto units need fuel <4 cSt; waste oil far exceeds that and will coke the burner within hours, so avoid it [Webasto Tech Doc, 2019; Elektroda, adria5n, #16944569].
What emissions and health risks does burning used oil create?
Used oil can contain 4 000 ppm lead, 800 ppm zinc, and PAHs. Combustion releases carcinogenic metal oxides and soot [EPA, 2010]. Forum users warn of heavy, unpleasant odour and smoke [Elektroda, freebsd, post #16978065]
How do I build a two-tank change-over system?
- Fit LPG-grade 12 V solenoid valve to feed diesel or oil line. 2. Start on diesel; when coolant >70 °C, flip switch to oil. 3. One minute before shutdown, switch back to diesel to purge thick fuel [Elektroda, zasilaczen, post #17215903]
What edge-case failures should I expect?
Cold weather sludge can block pickup screens below −5 °C, stalling the engine. A clogged return loop may also air-lock the system, preventing venting and causing rough idle [Elektroda, kwok, post #17216621]
Can I run on gear, fryer, or transformer oil instead?
Gear oil is thicker and sulfur-rich; dilute 50 % with diesel and heat aggressively. Fried vegetable oil works if filtered and pre-heated; many drivers report quieter engines [Elektroda, smutekh, post #16977741] Transformer oil is carcinogenic and legally risky; avoid it [Elektroda, freebsd, post #16978065]
How much money could I save?
If waste oil is free, fuel cost drops from PLN 7.50 /L diesel to PLN 0.80 /L for heating electricity and filters, saving about PLN 6.70 per litre. Annual 10 000 km use (6 L/100 km) yields ≈ PLN 4 000 saved. Offsetting fines negates savings if caught [GUS Fuel Prices, 2023].