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Old 04-16-2013, 05:01 PM   #1
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Exclamation Diesel cool down

I found a forum, <>. It it, the "expert" says idling a Diesel engine for more than just a few minutes can be detrimental. When I have to go to the dealership next week to have the Rhino bed liner sprayed in, I'm gonna talk with the service advisor about this. I'll come back with a full report!

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Old 04-16-2013, 05:05 PM   #2
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The practice of letting a diesel idle to cool down before shut down is and "OLD SCHOOL" practice from when the turbos did not have a waste gate system they have today and the exhaust turned the turbo at full speed all the time, thus the need to let the engine idle down for the turbo to slow down before engine shut down and cutting off the oil supply to the turbo.


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Old 04-16-2013, 05:47 PM   #3
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I really do feel as though so many of YOU have a lot of knowledge. It's nice that you share it with others! Both DW and I have picked up lots of tid bits.
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Old 04-16-2013, 05:59 PM   #4
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When towing with the 6.4 diesel, Ford recommends allowing the engine to idle 3 to 5 minutes to let the turbos cool down.

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Old 04-16-2013, 06:10 PM   #5
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My diesel mechanic strongly recommends to allow the turbo to cool. He advises me 2 minutes for normal driving. I go 2 minutes or 250 on the pyro. This is to prevent the oil from coking in the turbo and having a premature bearing failure. My book even says to allow for cool down.

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Old 04-16-2013, 06:11 PM   #6
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It is old school and it can still apply to engines today. But only if you have been hauling a heavy load, working the engine, and the turbo is VERY HOT! Shutting it down right away while turbo is hot tends to cook the oil into goo. I would not let it idle, just drive around soft for a few miles at moderate speeds to keep coolant and oil flowing. Then shut it down as normal after the engine and turbo have had a chance too cool back down to normal operating temps. If that isn't practical for your driving area, then an idle cool down works.
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Old 04-16-2013, 08:42 PM   #7
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Shutting down hot and the oil flow stops will cause the oil to cook on the turbo shaft. The when over time of starting and shutting down causes the turbo shaft and bushing to wear out. The over time the turbo fins start hitting the turbo housing and then it flies apart and it is sucked it the engine. I have seen this happen on heavy equipment engines. Then to repair the engine the Heads will have to be removed and clean the shredded pieces out of the engine. It this is not done it can cause a busted piston.
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Old 04-16-2013, 09:07 PM   #8
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The main reason for not idling a newer diesel is the DPF, or Diesel Particulate Filter. Under normal circumstances if a regeneration is needed it happens when driving down the highway. To do the regeneration the ECM dumps raw fuel into the cylinders during the exhaust stroke so it can burn the particles in the DPF. This process generates higher exhaust temperatures than normal. I know Duramax engines will throw a code if ECM determines the engine is idling it will halt the process. It will sometimes go into a low (no) power mode until you cycle the ignition, then take it out for a proper drive.

Take a look at the exhaust tip of a newer diesel truck, it is larger than the exhaust pipe and is not sealed to it. That is done so air can be drawn in and mixed with the exhaust to cool the exhaust gas down. The manufacturers don't want people or things getting burned by the exhaust gas when a regeneration is taking place. Inside the DPF the temperature is around 650 C or 1200 F. That will leave a mark.

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Old 04-16-2013, 09:21 PM   #9
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The DPF can handle a few minutes worth of idling, especially considering the risk of shutting down with a hot turbo.

At work we have two huge Caterpiller engines for propulsion, two medium sized Cats for generators, and a big rig sized Cat for a backup generator. All of them get an idle cool down before shutdown, and EGT must be at 350 or below. Large turbos are very expensive to replace.

Wastegate or not, turbos do need to cool prior to shutdown. I have an EGT guage on my truck, and even unloaded, can take up to a minute to reach 350.
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Old 04-16-2013, 09:49 PM   #10
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I do not worry if I am not towing, but if I have been running at 70 MPH for 3 hours towing the camper, when I stop to make the bladder gladder, I leave the engine running and lock the doors. I figure the risk of someone stealing it is less than the risk of ruining the turbo.

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