Why diesel filters block up in Canberra
RACQ names low-speed and stop-start driving as the most common cause of DPF trouble, because it stops the filter's self-cleaning (regeneration) from starting or finishing. An active regeneration wants the car at about 80 km/h or more for somewhere between five and 25 minutes.
In Canberra that's usually within reach. The parkways that link the districts generally run at up to 100 km/h, and the Tuggeranong Parkway holds that for most of its length. The diesel that never gets there is the one doing short trips on 50 km/h streets and through 40 km/h town centres.
RAA's suggestion is a weekly drive of 20 to 30 minutes at highway speeds. For most Canberra diesels, that's a loop on a parkway or a run some way up the Federal Highway.
Exhaust fumes inside the car
If you can smell exhaust in the cabin, open the windows, don't sit in the car with the engine idling, and have it checked soon. Exhaust gas carries carbon monoxide, which you can't see.
Exhaust jobs that come up in Canberra
White vapour on frosty mornings
A cold exhaust throws out condensation that looks like white smoke, and the NSW EPA says it normally clears once the car warms up. On a frosty Canberra morning that's expected. Thick white smoke that keeps coming once the engine is warm is a different story.
Blue, grey or black smoke
The NSW EPA says blue or grey smoke normally means engine wear, and black or grey from a diesel means incomplete combustion, from causes such as faulty injectors or a clogged air filter. That's a diagnosis job before it's an exhaust job. Smoke from the exhaust.
Rattles and blows underneath
A rattle under the car is often a loose heat shield or a broken hanger, and a blowing or ticking noise that's loudest from cold can be a leak. Gravel roads out to Namadgi shake exhaust mounts about, so mention any dirt-road driving.
When the DPF light comes on
Follow the owner's manual first, which often means a sustained drive. If the engine light is on too, RACV says another fault may be stopping the regeneration, so a code read comes before anything else.
Left too long, the car can drop into limp mode (reduced power to protect the engine). Then the mechanic has to run a forced regeneration, and RACQ says that can mean an oil and filter change as well, because of fuel getting into the oil.
What to ask before a DPF job
- Will you read the codes and find out why it didn't regenerate, not just clear it?
- Does the oil need changing after a forced regeneration?
- Is the engine oil the grade the maker specifies for a car with a DPF?
- What will the written estimate cover if the filter turns out to need replacing?
Our take
If you drive a diesel in Canberra and most trips are short, we'd make a weekly parkway run part of the routine before anything goes wrong. If the light is already on, we'd get the codes read straight away rather than wait for limp mode.