Fact-checking common car beliefs

RACQ Principal Technical Researcher Russell Manning clears up some common misconceptions relating to cars.

Speedos always read a bit high, so it’s safe to drive at a slightly higher speed than indicated

False.  Starting in 2006, speedos were required to either read accurately or higher than the vehicle’s true speed. Most have some degree of error, but some don’t, so unless you know your speedo’s error, you risk exceeding the speed limit if you do this. 

Lighter coloured cars are cooler inside than darker ones

True, sort of.  Our testing of parked vehicles has shown that the interior temperatures of a white car can be about 4°C cooler than for an equivalent black car.  However, with typical internal temperatures exceeding 70°C in Queensland’s summer, colour really doesn’t make much difference – it will still be really hot inside.     

Coolants can be mixed provided they are the same colour

False.  Do not mix coolants, even if they are the same colour.  Doing so can produce unpredictable and potentially harmful results.  




Window tinting reduces the interior temperature of parked cars

False.  Our testing has shown that the interior temperature of a parked car will eventually reach the same level regardless of whether it has tinted or clear window glass.  At best, tinting slows the temperature rise but it also causes the heat to be retained for longer.

A stocking can be used as a temporary fan belt

Unlikely.  This claim probably originated in the days when cars were very simple, and even then, it’s questionable how well it would have worked.  It won’t work with a complex modern car though. 

Shackles for trailer safety chains have to be a particular colour

False.  They do have to have sufficient capacity for the weight of the trailer being towed.

Using high-quality synthetic engine oil will extend oil change periods past the vehicle manufacturer’s specified intervals

False. Synthetic oils are designed to protect highly stressed engines not to extend oil drain intervals.  They still need to be changed when specified by the vehicle manufacturer.   

Load nets are mandatory on utes and trailers

False. Nets are an acceptable method of securing light, loose, loads but they are not mandatory. However, you must appropriately secure your load. The type of load must always be considered when selecting the appropriate method of load restraint.