My neighbor has a Dodge 3500 diesel, he drives me nuts ! everytime he comes home he leaves it idle for hours in his driveway before he comes out and turns it off, I complained saying that thing make a lot of noise and hes wasting fuel by leaving it idle for long periods of time, he told me im a stupid idiot and I don't understand a diesel engine, he said you have to leave any diesel idle after its been run hard so that the engine cools down, before its turned off, if he don't do that it will ruin the engine. I think he's full of it, I think it won't hurt any diesel engine shutting it down when the engine is hot, I mean the engine stays hot even when it is at idle. Am I right? Or is he right?

 

he's somewhat right ... it (the engine) needs to stablize the temps between the different parts ... but this should only take 30 mins or less.

I also have to do this during startup and shutdown on my airplane.

 

Unless he just got done pulling a huge trailer up a mountain pass, 30 seconds of idleing is enough. Tell him to read the owners manual.

 

Idleing it after it's been run hard or easy is a good idea but not for a long period of time. The reason you leave it idleing is to cool down the turbo and from my knowledge that is the only reason, not saying that there may not be another I just don't know it. Tell your neighbor to look into getting a turbo timer. He can set it to idle the engine for a certain temperature or an amount of time specified by him to reach the desired temp and then it will turn the engine off. 2-3 minutes is plenty of time to get the turbo to about 300* or lower.

 

Basically the issue is the turbo charger. At full load, exhaust temps can hit around 1200 degrees, and some of that heat conducts through the turbo shaft to the bearings.

While the engine is running, a high volume of oil is pumped through the bearings to keep them cool, and the flow of oil ensures that the oil doesn't get too hot.

If you shut the engine down while it is hot, the oil flow stops and it can carbonize the oil around the turbo bearings.

At idle, exhaut temps drop to about 300 degrees, so if you let it idle for a bit, the flow of cooler air will carry the heat off the piston tops and turbo. Then when you shut the engine down, the oil that stops in the turbo bearings won't hit temps that would break the oil down.

Anyhow, he is somewhat correct, but if he's running low speeds (ie in town) without a significant load, there is no need to idle the engine more than a minute. If he just pulled 20,000 up the mountain at freeway speeds, then 5 minutes of idling would cool it down adequately. Installing a pyrometer is nice, in that it takes the guesswork out of how hot the turbo is.

Actually, if he really is letting it idle for hours, doing so in cold weather followed by shutting down the engine can cause damage. Modern diesels run cooler combustion temps to reduce emissions, and at idle in cold weather the exhaust valves may not be hot enough to burn off deposits and goo from partly burned fuel (called wetstacking). The problem is, if you shut down the engine, you may have an exhaust valve stick as the deposits cool and solidify, which can bend a pushrod at the next startup. The owner's manual for his dodge likely warns against prolonged winter idling...

 

I had an 04 Dodge Cummins and it seems to me that the owners manual recommended letting it idle for 4 or 5 minutes on startup and after you've run at highway speeds. I'd think that 5 minutes would be more than enough to let it cool down. I usually only let it do that after towing the hauler home. Then it idled for about 5 minutes while we were parking the trailer and unhooking.

Tell him to shut the d@mn thing off.

 

Actually, my truck's starting instructions on the visor say to let the engine idle for at least 30 seconds after starting the cold engine in temps below 66 degrees, and to idle longer in sub zero temps.

For cool down, the manual says for stop and go driving with no load idle less than a minute; and stop and go driving with a medium load is one minute; freeway driving with a medium load two minutes, city traffic at max gross combined weight three minutes, highway speeds at max combined weight, four minutes, and after pulling an uphill grade at max combined weight, five minutes.

It also says: "Avoid prolonged idling. Long periods of idling may be harmful to your engine because combustion chamber temperatures cand drop so low that the fuel may not burn completely. Incomplete combustion allows carbon and varnish to form on piston rings and injector nozzles. Also, the unburned fuel can enter the crankcase, diluting the oil and causing rapid wear to the engine."

Anyhow, the manual pretty much agrees with what I posted.

 

This guy lets it idle for hours, at least 2 hours, sometimes 3 hours, his driveway is closer to my house than his house, so Its louder for me, I think he either forgets about it, or he falls asleep, he braggs and he think hes special cause he has a diesel like he's a trucker or something.

 

Idling his motor for about 3-5 minutes is about right. Anything more, without coming out to drive it within a hour, is a complete waste of fuel. Check with your local laws and find out about the anti-idling laws that are mandated in your area. I know if you live in New York, its 5 minutes. Not sure about PA. See if you can then report him.

 

Yes, Pittsburgh HAS a anti Idling Law...... 30 minutes