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Discussion Starter #1
I recently had a diesel engine in a 1995 GMC fleet truck rebuilt. Asked the mechanic if there was anything we could do to prolong the engine life while running this new rebuild or my new 03 Duramax.


Also asked if I should be turning off the engine when running into a store for 5-15 minutes or let it run? This is due to having below freezing temps here for close to 6 months of the year.


Mechanic stated that it is fine to turn the engines off but recommends to let the turbo spin down for 2-3 minutes first. This was due to past experience with turbo bearing problems & required replacements.


I have a couple questions if anyone could answer:


1. Should I let the turbo spin down for 2-3 minutes before turning off the engine? if so, for how long?


2. If the weather if below freezing or down right nastily cold (colder than -20'C), should I let the engine run when re fueling or running into the store for 5-15 or 20+ minutes?


Any suggestions would help.


Thanks!
 

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I was wondering the same thing. I know it is generally considered good practice to do this to avoid coking in the turbo. We used to do it on a turbo Starion we had, and I do it when possible in the truck, but not always. Usually I will park, then get my stuff together or whatever, then the lat thing I do is shut off the motor and get out.

If this is something I should be doing, I will start. Thanks for asking, I'm looking forward to some replies...
 

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Not shutting down is a remnant of the diesel days of old when starting diesels was difficult. Even more difficult as it got colder.


With the newer trucks there are a lot of improvements that made starting no where near the issue it was. Actually reports are finding that you do more damage by leting your truck idle for prolonged periods: Unburnt fuel in the crank case, cylinder wall wash, clogged injectors, carboned glow plugs, wear and tear in general.


You might be a little confused about waiting 2-3 minutes for the turbo to spin down. The turbo spins down and up instantly and directly proportional to the amount of exhaust gas flowing (Your foot on the throttle.)


I think you mean cool down. Accuratly speaking the rule of thimb is you want the Exhaust Gas Temperature (EGT) down to 300 degrees before shutdown.


If you don't have an EGT guage, unless you just came off the highway doing 55+, by the time you slowly drive around the lot to park you are cooled down enough.


Even if you just stopped from prolonged high speed, a minute tops is more than enough to cool down the exhaust gas.


BTW. around here in NJ. If you left your truck running while you went into the store for 5-15 minutes. You won't have to worry about prolonging the life of YOUR truck
.


Edited by: JohnnyO
 

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JohnnyO said:
With the newer trucks there are a lot of improvements that made starting no where near the issue it was. Actually reports are finding that you do more damage by leting your truck idle for prolonged periods: Unburnt fuel in the crank case, cylinder wall wash, clogged injectors, carboned glow plugs, wear and tear in general.

I can't speak to the Dmax directly since I don't have mine yet, but I've been around diesels and turbochargers quite a bit.


With the big Detroit Series 60 that's in my Fire Truck, one of the biggest problems is the thing getting too cold while idling at a scene, so all of the newer trucks have a high idle system to try and keep them a little warmer. If they get run too much cold, you can glaze the cylinder walls and they start burning oil as well as the problems mentioned by Johnny O.


As far as the turbo spin down, getting some of the excess heat out is important. But one of the primary reasons is that due to the high RPM turbos operate at, it can take a little bit for one of them to spin down if it's been operating at a high power setting. Since the housings for the turbo experience such dramatic temperature changes, (resulting in expansion and contraction at different rates of the metals they are made of) trying to get a bearing to live in that environment is just not possible. So the center shaft actually rides on a cushion of oil provided by un-metered oil pressure from the engine. If the turbo is really spinning and you shut off the engine, the oil cushion that the center shaft is riding on disappears...


So yes it's a good idea to let it spin down, but unless you've just been pushing the hell out of it, the idling while getting around the parking lot or into the garage should do it.


Maybe Eric can tell you what a turbo on a Dmax spins at, I don't know, but the Garrett turbos on light aircraft spin at upwards of 90,000 RPM when at high power settings.
 

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...actually it is quite possible, alot of race turboes use ball bearings. we have a video of a buddies taking roughly two minutes to stop spinning after a dyno session..pretty neat.
 

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Discussion Starter #6
Thanks for the replays guys. Zeeb, you basically summed up what the mechanic told be, but I as well do not know if this would be the same for the Duramax.


I am installing a high idle switch this week. As we speak, my exterior truck temp gauge shows -24'C (-11.2'F).


Can anyone suggest if I should shut the truck off or keep it running while I fill with fuel or run into the store for 5-10 or 15+ minutes or more if the outside temp is below freezing?


Thanks.
 

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I would personally keep the truck running. Running it for 15min I do not think will hurt anything...I think shutting it down and starting it up a few times times a day in those temps would do more damage than running it for 15min at 1250RPMS
.


Just my thoughs, not in stone.


JohnnyO,


Were in Jersey? My wife and I were born and raised in the Northern part of the "Garden State"...We thought we'd never say this but we living there.
 

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Another good reason for Synthetic oil.......won't cook out of the bearings! Mobil Delvac 1 all the way!
 

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I could write all of my knowlege on turbos on a match, and have room to spare. So if this is a load of B.S., please let me know.



The other day I came across an ad for a device that is supposed to allow a diesel engine to idle for a few minutes after the ignition is shut off, thus allowing the egt's to reach a "safe" level, after which time, the unit will shut down the engine. The setup was around $100-$120 IIRC.


Has anyone heard of this, and if so, would it work on our trucks?






Kevin
 

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ZEEB, your high idle is for emissions purposes, not 'cause the engine runs too cold at an idle. Turbo cool down is goods, but doesn't take long. A 5oo horse detroit series 60 cools down to 300 degrees in less than 2 minutes, after being driven like a wild banshee on an emergency response. L8R y'all!
 

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Aren't our turbos water cooled? I have thought they were and so it is only good to let it sit for like 30 sec to a minuet?
 

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FILO said:
ZEEB, your high idle is for emissions purposes, not 'cause the engine runs too cold at an idle. Turbo cool down is goods, but doesn't take long. A 5oo horse detroit series 60 cools down to 300 degrees in less than 2 minutes, after being driven like a wild banshee on an emergency response. L8R y'all!

Well possibly, but that's not what Pierce, Detroit and our maintenance folks say.... Besides that, if it were for emissions, it would be automatically engaged, ours are all manual. And they are the 500 horse Detroits, with Allisons.....
 

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Unless you just pulled to the side of the road immediately after turning your turbo red hot, I don't think we need to worry about it. The water cooling should do an adequate job of keeping the bearing temps way out of coking range.
 

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So, what's the verdict on the turbo timer? Totally unnecessary, a good idea, or what? sounds like there isn't really a need for something like that except for rare ocassions, but would it be worth getting one for those times, or is it a waste of time and money?





Kevin
 

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Kevin, I think the "turbo timer" is unnecessary on a DMax. With improvements in bearings, oils and the water cooling of the DMax turbo there should be no value added with this device. Something that WOULD be beneficial to any engine would be a pre-oiler that uses a pressurized accumulator to pressurize the oil galleries prior to cranking, but they are difficult to mount and plumb and you run a risk any time that you tap into your lubrication circuits.
 

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Idle_Chatter said:
Kevin, I think the "turbo timer" is unnecessary on a DMax. With improvements in bearings, oils and the water cooling of the DMax turbo there should be no value added with this device. Something that WOULD be beneficial to any engine would be a pre-oiler that uses a pressurized accumulator to pressurize the oil galleries prior to cranking, but they are difficult to mount and plumb and you run a risk any time that you tap into your lubrication circuits.




Thanks,


That's pretty much what I thought after what's been said here, but then again, I never knew about the need for extra filtration, among other things, until I joined this site.


Sooooooo many questions.






Kevin
 
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