Holden SUV Range

Noises are impossible to diagnose without actually hearing them. So you need to take the vehicle to a mechanic and get the car to produce the noise you’re reporting. That may involve leaving it overnight or otherwise reproducing the circumstances under which it misbehaves. Experienced mechanics can often tell whether a noise is important or just wear and tear, and act accordingly.

For the record, your mystery noise could be anything from a worn turbocharger, a sticking hydraulic lifter, piston slap, bearing knock or even something as weird as a loose baffle in the exhaust system. All these things can manifest as random and metallic noises, and they range from simple to catastrophic in magnitude.

For a start, you might find it’s neither of those things causing the noise. You may have a worn tyre, poor wheel alignment or a faulty brake, to name just a few possibilities. That said, both your suspects are likely contributors to this type of noise.

In any case, there’s a simple way to tell whether a noise is coming from the driveline (engine and transmission) or from one of the wheel bearings. Drive the car at whatever speed is necessary to make the noise appear. If it gets louder as you apply throttle, there’s a good chance it’s driveline related.

But now, with the car still making the offending noise, drop the transmission into neutral (where it’s safe to do so, of course) and let the vehicle coast. This takes all the stress off the driveline and the engine should return to idle. If the noise is still present, then you have a wheel bearing or other problem linked to the wheels, brakes or axles, but not the engine or gearbox.

If your diagnosis is correct, the problem will be with the either sensor that detects the temperature of the coolant, the computer that creates the signal to open, the wiring that carries the message or the thermostat itself. An auto electrician should be able to sort this out by testing the components one by one until the dud one reveals itself.

But there’s another possibility in cars like this one with a thermostat that lives in a plastic housing. Over time and repeated heat cycles, the plastic can degrade and fail internally. At that point, the actual thermostat mechanism can move sideways and jam against the housing, effectively preventing it from opening., At that point the engine can overheat. Don’t rule that out until the condition of the housing has been checked.