If you’ve ever pulled up at a busy Hamilton intersection – maybe Te Rapa, or over in Hillcrest – and noticed a worrying knocking sound under the bonnet, you’re not alone. Engine knocking is one of those classic NZ car problems we see all the time here at Grimmer Motors, from Morrinsville to Cambridge and even up those potholed roads near Rototuna. Here’s five reasons that annoying engine knock might be popping up… and how you can get it sorted before you end up stranded in traffic on Normandy Ave or stuck outside The Base on a Saturday!
1. Low-Quality Fuel (Wrong Octane or Dodgy Servo)
One of the most common things we see – especially with folks running European cars like a Peugeot 308 or a Volvo V40 – is using the wrong fuel. If you put 91 in a car that needs 95 or even 98, you’re asking for trouble. Dodgy fuel (from a servo that hasn’t had a tanker in a while) can also make your engine rattle like a shopping trolley.
- Check your car’s manual for the exact octane rating it needs – some Japanese imports are fussy!
- Stick to reputable stations with decent turnover.
- If you suspect bad fuel, a quality octane booster might help – but don’t overdo it.
A good fill-up keeps your engine humming – less knocking, better economy.
Learn more about improving fuel economy
2. Faulty or Tired Spark Plugs
Spark plugs cop a fair hiding, especially on those stop-start missions from Nawton to Chartwell or crossing Frankton in peak traffic. We had a lady in last week with a Honda Fit – her engine was knocking because two plugs were shot, probably hadn’t been changed since it came off the boat.
- Have your plugs checked out every service – roughly every 30,000km for most cars.
- Use plugs suggested by the manufacturer – don’t mix and match random ones off TradeMe.
- Tired plugs mean rough running, more knocking, and worse fuel use.
Catch spark plug issues early for a much smoother ride.
More on spark plug maintenance
3. Carbon Buildup in the Combustion Chamber
With all the cold starts on foggy winter mornings or puttering through Glenview’s 50km/h zones, carbon can build up, especially in Mazda Demios and Suzuki Swifts. Over time, that muck makes the bang in your engine less precise – cue the knocking.
- Run a decent fuel system cleaner every now and then (ask us for what’s actually worth the money!)
- If you’ve got a proper buildup, you might need a workshop clean – not cheap, but much better than a new engine.
- Adhere to regular servicing to keep things cleaner inside.
Stay on top of carbon and your engine will thank you.
Understanding engine performance
4. Ignition Timing Out of Whack
This crops up on everything from turbo Subarus to Toyota Corollas – if your timing is off, the “bang” happens at the wrong moment and it’ll knock. We had an Auckland customer with a Lexus IS250 moved to Tamahere; after a botched timing job up north, her engine was pinging all over the place.
- Let a proper mechanic check and adjust your timing. You can’t fix this with guesswork.
- Stick to the service intervals – timing belts and chains need love too.
Spotty timing means poor engine health and can mean WOF trouble later.
Signs your ignition system needs repair
5. Poor Engine Tuning (Not Just for Boy Racers!)
You don’t have to own a Golf GTI to benefit from a tune-up. A lot of hybrids and late-model Kias, Toyotas, and even the odd old-school Nissan Bluebird knock because the software or sensors are out of sync. Seen it loads, especially after rough backroad driving near Raglan or Te Kowhai.
- Book your engine in for a regular tune – at least once a year, or if things feel “off”.
- Let the pros update sensors and tweak things so everything runs true.
A well-tuned car is happier, uses less fuel, and stays on the road longer.
More about engine tuning
Conclusion
The short of it? Don’t ignore that knock. Whether you’re running errands on Victoria Street or heading out to Cambridge for a weekend, catching engine issues early always saves money (and stress). Your car will last longer and won’t leave you stranded when you least expect it.
Why Come to Grimmer Motors?
We’ve helped drivers all over Hamilton and the Waikato keep their engines sweet for over 50 years. You get straight-up advice, experienced tuning, and friendly people who actually listen to what’s bugging you about your car. No job too weird – from hybrid repair to full car service Hamilton-wide, we’re here to help.
Got a knocking engine? Or just need some honest advice and a proper look under the bonnet? Book in below and let’s get your wheels sorted.