What the experts say
According to Danie Josling, senior manager at Nissan South Africa’s dealer training and technical centre, it isn’t advisable to have an engine running at idle speed for extended periods of time.
“One of the major concerns could be engine oil dilution with fuel, resulting in compromised lubricity accelerating engine component wear. Another concern is carbon which is a by-product of combustion which causes build up on internal engine components effecting their durability,” says Danie.
Over at Toyota South Africa’s technical services division, they don’t say that it’s harmful for an engine to run at idle rpm, but do mention that if a vehicle is going to be used like this for the majority of the time (think game-viewing vehicles that don’t leave a reserve), that the engine oil be replaced every 5 000 km as stipulated in the Toyota owner’s manual.
BMW’s also not too keen on idling for extended period of time, because of the richer mixture than is ideal, which causes a build-up of soot. “A sporty drive or episodes of rapid acceleration after a day of game driving should clean out any residual soot,” says Sibusiso Mkwanazi, manager of group product communications at BMW South Africa.
Roland also wanted to know if the oil flow is impeded in any way if the engine speed isn’t sufficient to build up higher boost, but Danie assured us that oil pressure for engine speeds are predetermined and will be maintained at the designed pressure for idle speed.
Sibusiso confirmed that the oil-flow requirement to the turbo is low compared with other components and that oil flow and pressure under all conditions is ensured by the oil pump and engine mapping.
“The oil acts to dissipate heat, which is negligible during idle,” adds Sibusiso.
In Roland’s case, Danie says that if you follow the Maintenance Under Severe Conditions recommendations in the Nissan owner’s manual, which requires the oil and filters be replaced more frequently than usual, then technically you should be okay. And because he services the vehicle every 15 000 km, this is likely why Roland hasn’t suffered any longterm damage so far given that his trips only result in around 600 km worth of this kind of low-speed driving annually.