Is leaving an engine idling for hours at a time while we run surveilance missions ruining our engines?

Dear Car Talk

Dear Car Talk | Apr 01, 2004

Dear Tom and Ray:

I work in law enforcement on a surveillance unit. We often have to sit in our vehicles for long periods of time, sometimes with the engine running. Is it hard on a vehicle for it to idle in a stationary position for long periods of time -- and why or why not? If it is necessary to remain stationary with our vehicle idling, is it better for the vehicle to be in Park or Neutral, or something else? I just want some solid, expert advice to help our fleet of vehicles and perhaps save some taxpayer money. -- Jerry

TOM: Well, the less time an engine spends running, the longer it's going to last. That's obvious, right? An engine that has 100 hours on it will last longer than an engine that has 10,000 hours on it. That's why we don't recommend that people buy used taxicabs. Or used police cars!

RAY: So, if you don't need the engine on to keep from freezing, or to keep from melting, turning it off is best. That saves gas, saves money and decreases pollution.

TOM: But if you need to leave the engine running, aside from the normal wear and tear, no additional harm will be done to it. You can run a modern engine at idle all day and -- as long as the cooling system is in working order -- nothing will break.

RAY: And Park is definitely the best gear to use so you don't do what? Roll into someone else's car. Which tends to blow your cover.

TOM: In the old days, when cars had carburetors, fuel metering was so imprecise that the carburetor would pour way too much fuel into the cylinders at idle. Some of that fuel would inevitably seep down into the crankcase and dilute your oil. And that was bad for the engine.

RAY: But nowadays, all cars are fuel-injected, and the computer instructs the injectors to deliver just the right amount of fuel for any situation. So, oil dilution isn't a problem when you're idling.

TOM: The only thing to watch out for on a surveillance mission is what we learned from Lt. Frank Drebin: Watch out that you don't create a 4-foot-high pile of pistachio shells outside the driver's door. It can make it hard to open the door and go after the perp, Jerry.

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