Red oil light, or smoke from under the bonnet? Pull over
The oil light means oil pressure has dropped, and an engine running without it can be badly damaged quickly. Pull over somewhere safe and switch off, and don't restart it to see if the light goes away. Oil dripping onto a hot exhaust can smoke and catch fire: if there's smoke from under the bonnet, get everyone away from the car and call 111.
Is it definitely oil?
AA New Zealand's guide to leaks sorts them by colour. Brown, black or amber is usually engine oil. Bright green, orange, pink or blue is coolant; red that browns with age is automatic transmission fluid; and clear water after a drive on a humid day is usually the air conditioning draining, which is normal.
Slide a sheet of cardboard under the engine overnight. In the morning you'll see the colour, the size of the patch and roughly where it's coming from.
Where's it coming from?
| What it looks like | Usual fix | |
|---|---|---|
| Rocker cover gasket (top of the engine) | Oily around the top, running down the sides, sometimes a hot-oil smell | A new rocker cover gasket |
| Sump plug or oil filter | A drip low down, often soon after a service | Back to whoever did the service |
| Sump gasket | Oil around the pan at the bottom of the engine | Resealing the sump |
| Crankshaft seals | Oil at the front of the engine, or between engine and gearbox | New seals; the rear one means the gearbox comes out |
| Turbo or oil cooler lines | Wet around pipes and fittings | New seals or lines |
Why did it start leaking just after a service?
AA New Zealand says the usual suspects on a newer car are a faulty sump plug gasket or a leaking oil filter seal, both disturbed at an oil change. Take it back to the garage that did the work. Under the Consumer Guarantees Act a service has to be done with reasonable care and skill, and Consumer Protection's advice is to go back and give the mechanic the chance to put it right.
What to do this week
Check the dipstick
On flat ground with the engine cold, pull it, wipe it, dip it again and see where the level sits between the marks.
Top up if it's low
Use the oil grade in the owner's manual, a little at a time, and don't overfill.
Measure the drip
Cardboard overnight. A coin-sized spot and a dinner-plate patch are very different jobs.
Send it with the evidence
Photos of the cardboard and the dipstick, and how often you've had to top up, go in the note.
What the mechanic will check
They'll clean the area and trace the leak from the highest wet point down, because oil runs and gets blown back along the underside. Sometimes they add a dye to the oil and look again after a drive.
Ask whether the leak is near the exhaust or any rubber parts. Oil on a hot exhaust is a fire risk, and oil soaking into rubber bushes or belts shortens their life.
A WoF isn't a check of the oil: the MTA says lubricant levels and condition aren't part of it. Don't read a pass as a sign the leak can wait.
What you can do, and what to leave
You can
- Check the oil level weekly while it's leaking, with the engine cold and the car level.
- Top up with the grade the manual gives.
- Put cardboard down to measure the drip.
Leave to the mechanic
- Cleaning the engine and tracing the leak.
- Gaskets and seals, from the rocker cover to the crankshaft.
- Checking whether oil is reaching the exhaust or rubber parts.
What we'd do
We'd check the dipstick, put cardboard down for a night, and send a photo of both with the job. A slow seep from the top we'd have fixed at the next service; a fresh patch every morning, we'd want seen this week.