Wrong fuel or AdBlue in the tank?
Don't turn the ignition on, not even to check the gauge. AA New Zealand says many vehicles have a pump in the tank that runs the moment the ignition goes on, and it'll push the wrong liquid through the system. Petrol in a diesel strips the lubrication the fuel pump depends on, and AdBlue in a fuel tank is just as serious. Tell the station staff, and ring your roadside cover to get the tank drained before the engine runs.
What's different about servicing a diesel?
Less than it used to be. AA New Zealand says many modern diesels now have service intervals much like a petrol car's, though the maker's schedule for your vehicle is what counts.
The differences are in the detail. Diesel engine oil carries a lot of soot, so the grade and specification in the handbook matter, especially on engines with a particulate filter. The fuel filter does more work too, catching water as well as dirt before it reaches the injectors.
One thing that isn't the mechanic's job: road user charges. Diesel isn't taxed at the pump, so diesel vehicles pay RUC, and AA New Zealand counts keeping it current as part of owning one.
What is AdBlue, and what if it runs out?
AdBlue is a brand name for diesel exhaust fluid, a non-toxic mix of urea and purified water. It lives in its own tank and is sprayed into the exhaust, where it breaks the harmful nitrogen oxides down into nitrogen and water.
The vehicle gives you a run of warnings as the tank gets low. Take them seriously: AA New Zealand says the electrics won't let the engine start once the fluid runs out. You'll find it at most truck stops, but read the pump label first, because some truck stops sell it from the same pumps as fuel.
Smoke, lost power and the particulate filter
Most modern diesels use common rail injection: one shared rail holds fuel at very high pressure, and the engine computer decides exactly when and how much each injector sprays. When a diesel smokes, misses or loses power, the injectors, the turbo, the air intake and the particulate filter are the usual places to look, and a good mechanic tests rather than guesses.
If a particulate filter light is on, exhaust and DPF repairs explains what happens next. For injectors and turbos, see fuel injector repairs and turbo repairs.
Questions to ask a diesel mechanic
- How many diesels like mine do you work on?
- Can you test the injectors and the fuel pressure without taking them out?
- Which oil will you use, and does it suit a particulate filter?
- Will you replace or drain the fuel filter at this service?
- Will you check the AdBlue system and the particulate filter while it's in?
What a good written diesel quote shows
- The maker's service by name, with the oil grade and specification.
- The fuel, air and oil filters, each listed.
- Any fault codes read, and what they point to.
- Test results behind any injector, pump or turbo being replaced.
- A promise to ring you before doing anything that isn't on the quote.
Diesels and the WoF
The exhaust and the fuel system are both on the WoF list, so a leaking injector line or a blowing exhaust is worth sorting before inspection day. A diesel that's smoking heavily is also worth a look first, rather than finding out from the inspector.
What you can do, and what to leave
You can
- Check the oil level on a cold engine, on flat ground.
- Top up AdBlue only through its own filler, the one the handbook shows, never the fuel filler.
- Photograph any warning light along with the odometer.
- Note the colour of any smoke and when it appears: cold starts, hills, or all the time.
Leave to the mechanic
- Injector, fuel pump and rail pressure testing.
- Particulate filter cleaning and regenerations.
- Draining and flushing after the wrong fuel.
- Faults in the AdBlue system.
If it were our car
We'd pick a garage that does diesels every week and give them the symptom plainly: the smoke colour, when it's short of power, and which light is on. Ask for the codes and test results before injectors or a turbo get replaced, because those are big parts to replace on a guess.