Can I put marine diesel from my boat into my car?
I've got about 100 litres of marine diesel left in my yacht's tank, and she's coming ashore for the winter. Rather than letting it sit and grow bug, can I just siphon it out and put it in my diesel estate car?
Answer
You cannot legally put marine diesel in your road car because it is dyed red and carries a much lower tax rate, making it a serious customs offence. While older mechanical car engines will run perfectly on it, modern common-rail diesels suffer costly exhaust and fuel pump damage from the different chemical makeup.
The legal trap
Marine diesel supplied at UK boatyards and marinas is officially known as marked gas oil. It is dyed red and contains chemical markers to indicate that the rebated rate of duty has been paid for marine, heating or agricultural use. Road vehicles must use standard white diesel (DERV) which carries the full fuel duty.
If HMRC or the police catch you running a road car on red diesel, expect an immediate £500 minimum fine, vehicle seizure and a bill for backdated duty. The red dye and its chemical markers permanently stain the plastic of your fuel tank, fuel lines and filter housings. Even if you run 100 litres of red diesel and then switch back to white for a year, a roadside dip test will still show positive for the marker. You will then have to prove you are not a serial tax evader.
Chemical differences in diesel
Marina pumps dispense a chemically different liquid to petrol station forecourts.
- FAME content: Road diesel (EN590 standard) contains up to 7% biodiesel, known as FAME (Fatty Acid Methyl Ester). Most UK marinas supply diesel without FAME because biodiesel absorbs water and promotes diesel bug in damp boat tanks.
- Sulphur levels: Road diesel is Ultra Low Sulphur Diesel (ULSD), capped at 10 parts per million (ppm). Marine diesel can legally contain up to 1000 ppm of sulphur, though many marinas now supply a 10 ppm sulphur variant to comply with inland waterway rules.
- Lubricity: Modern road diesel contains specific lubricating additives. Marine gas oil often lacks these compounds, presenting a major problem for road vehicles operating at much higher engine speeds and injection pressures.
Marine diesel in cars
Pre-2005 vehicles with older mechanical injection systems will burn marine diesel without a mechanical hiccup. Heavy, low-pressure engines like the Land Rover Defender 300Tdi or Peugeot XUD are notoriously unfussy.