How bad is idling for your engine?

Question

I’m looking to buy a retired police vehicle and I came across a 2016 Dodge Charger with a 5.7L v8 Hemi for ~$14k with ~104k miles. It looked like an ok price but I saw the engine hours and it’s at ~10k idle engine hours and ~13k total engine hours. I’m trying to figure out if I should even consider buying it. (Btw I’m not too knowledgeable on cars so I hope you understand if the question wasn’t very good)

Answer 1

It's worth considering, but negotiate the price down as much as possible. In my experience, an engine that idles continuously has about twice as much wear as an engine that is driven normally.

It's bad to idle an engine, but how bad depends on a number of factors: oil change intervals, cold weather operating conditions, average duration of run time (i.e., frequent warm-up periods), engine design, and the amount of deposits on internal components (particularly fuel injectors and spark plugs). The most important of these is oil change intervals, because at idle raw gasoline seeps past piston rings, which dilutes motor oil's lubricating properties, and relatively weak compression results in poor combustion, which in turn promotes sulfuric acid buildup in the crankcase oil. If service records are available, oil change intervals should ideally be under 3,000 miles and less than one year.

Test drive the car. Crucially, have someone cold start the car and look for minute amounts of white/gray/blue smoke from the tailpipe, revealing worn ring seal and basically a bad engine. With the hood open, listen deep inside for any taps, clicks or rattles, especially if the sounds change when you raise the idle. When driving the car, after warm up, feel for hesitation under both heavy and light acceleration. Note any audible ping (detonation), especially while cruising at a very steady, 60 MPH speed. Look for shake and vibration in the steering wheel and interior while waiting at a stop light. These are signs of large deposit buildup, poor compression and excessive wear in the valve train. When finished with the drive, with car in Park and your side door open, raise and hold the idle to 3,500 rpm, then gradually ease down to 2,800 and 2,600. Any rapping sound indicates worn main bearings, an engine that is not serviceable.

I have owned a car since new for 30 years that idled most of the time in dense, urban traffic and rarely went above 20 miles per hour. The oil was changed annually, under 3,000 miles. At 50k miles, the engine consumed some oil, vibrated at idle, and lost acceleration and horsepower, about like other cars at 100k miles. I should note that many other people who drive cars in the same environment have engines that sound & run much worse, but seem to drive tens of thousands of miles more without complete failure.

An idling police car likely fared better than my idler. Periodic, emergency driving doubtlessly involved full throttle acceleration, which reduces deposits and thus promotes engine health and longer life.