Being a new LBZ owner I'VE just got to ask this dumb question. From what I have observed in the past it seemed that before people shut down thier diesel truck they would let it idle and cool down for a few minutes. Is it necessary to do this with the modern Duramax engines and for how long?

just take the 5 seconds to let everything spin down if driven normally, and a longer 2-3 minutes 'cool down' if you just got done flogging it and/or towing a large load. no real science to it that i know of, sooner or later you'll get a feeling for what's necessary. idea is to let the turbo slow down so when you shut 'er down the lack of oil pressure in the charger doesn't fry the bearings.

Ditto.
If you install a pyro, anything under 400 pre-turbo with the engine idling for at least 5-10 seconds is cool. If you want to be anal, shut down the AC and in a couple of minutes it'll drop to 300 or so, but that's really overkill.

By the time you get into a parking space from a normal drive, you'll be near 400. The only time you really need to be concerned would be, say stopping at a rest area at the top of a long grade, especially pulling a trailer. You either want to give it some cool-down time, or have everyone hit the rest-room one at a time and just let it idle with someone in it.

The LAST think you want to do is gun the throttle and kill the ignition.

I knew that you guys would respond in a fast manner with great info. This fourm has alot of people that has alot of experience with the Duramax diesel.

I bought the 2500HD D/A back in December 2005 and it has been cold most of the time and the engine has not got anywhere near 210 except the day I towed the hunting camper back home on a 245 mile trip. Mainly what I do is pull into the parking space at the location I going and let it idle maybe 4 or 5 seconds. I let my brother in law drive it one night and he ask me if he should idle it down before shut down and I told him no. During his test drive he got on the pedal pretty good from about 20 MPH and he felt the mighty power of the LBZ. He said man you could drag race with this truck. I said yep its done everyday. I think I just sold him on getting him a Duramx.

I love my new Truck...:grd: ...its the most powerful vehicle I have owned and my wife likes it too. ):h

One of the most common reasons for pre-mature turbocharger failure is "oil coaking". Oil coaking is basically burnt oil which leaves a sticky tarnished film on the bearings and the bearings will eventually sieze up. This is caused by shutting off the engine after towing or hauling a heavy load, without a proper cool-down for the turbo while it is still very hot. The turbo housing and bearings can become as hot as an exhaust mainfold, in fact I 've seen a turbocharger and it's insulated linner glow a orange color at night. The hot oil trapped in the bearings of the turbo begins boil or burn off the lubricants of the oil, thus causing the oil to coak and tarnish the bearings. If you have ever seen an oil leak on an exhaust manifold, it leaves this "oil coaked" residue.

Whenever I pull off the interstate to refuel, I let the engine run while I fill up or let it cool down for 3 to 5 minutes prior to shut down. That gives adequate time for the oil to flow thru the bearings and remove the exessive heat. :D

I just got a Viper alarm that has remote start and an adjustable turbo timer. I plan to use the turbo timer mostly after long hauls and whenever I am towing.

The reason for letting your diesel idle before shutting it down is for proper cooling of the turbo. If you shut your truck down too quick in cooler areas your hot turbo could cool too fast and crack. We all know metal expands when hot so shutting it off while the turbo is still hot could do so damage. Im saying in cold conditions, if its warm there is nothing to worry about.

Uhh.... no.... sorry, it doesn't work like that unless you happen to park in a vat of liquid nitrogen :rolleyes:

When you shut down, there is a period called "hot soak" where heat from the engine migrates through ALL components and actually evens out temperatures. Cylinder temps begin to drop, while the alternator and other accessories actually get hotter after shutdown, as well as overall underhood temperatures.

You aren't going to crack anything any more quickly by shutting down with the turbo at 800 degrees compared to 300 degrees.

I basically only use my truck for towing and have the SPA digital guage. Even after heavy towing the truck never takes more then 4-5 minutes to drop temps to a safe EGT reading. If you have no guages then I would wait 4-5 minutes after towing and only 2-3 minutes before shut down if running empty. I usually shut down between 275* and 305* degrees based on the guage reading, and the probe is mounted in the passenger side manifold.

I used to do a 2 or 3 minute cooldown on my gasser when I was towing my fiver. There is a lot of heat left in the engine systems when you shut it down after a hard run.

It's only prudent to do a cooldown on the DMax after a work run, to get rid of a lot of the residule heat. The turbo is the critical component and running cool oil through it to cool it down after a hard run is cheap insurance.

The reason for letting your diesel idle before shutting it down is for proper cooling of the turbo. If you shut your truck down too quick in cooler areas your hot turbo could cool too fast and crack. We all know metal expands when hot so shutting it off while the turbo is still hot could do so damage. Im saying in cold conditions, if its warm there is nothing to worry about. Theres no way your turbo could crack if it cooled down to fast unless you hit it with icy cold water when its very hot but that goes with anything.

The rate of temp change has everything to do with fatigue, and the numbers that go with MTBH. Jtyler is completely on with his statement. It is especially prevalent for turbos that are more air cooled, as in SE aircraft. It is also a factor in auto applications, we just don't discuss it much. If you want the turbo to last a long time, design in thermal mass to keep thermal swings to a minimum.

Coking is another issue, and an important one. What I don't understand is why anyone would monitor EGT as a barometer of a safe shutdown. You can have 250 degree oil in the bearings with a 350 EGT, and a turbo that is still 900 degrees red. It is the temp of the turbo mass that conveys heat to the now stagnant oil.

Hamops, good post. It would make sense to me to monitor oil-out temps.

What I don't understand is why anyone would monitor EGT as a barometer of a safe shutdown. You can have 250 degree oil in the bearings with a 350 EGT, and a turbo that is still 900 degrees red. It is the temp of the turbo mass that conveys heat to the now stagnant oil.
'cuz we ain't got nuttin' better! :)

By the time EGT has dropped to 300, it's pretty unlikely that the turbo will still be at 900. Not impossible, but not likely.

'cuz we ain't got nuttin' better! :)

By the time EGT has dropped to 300, it's pretty unlikely that the turbo will still be at 900. Not impossible, but not likely.

Rich, you're comment about not having anything better got me to thinking. I'm at work so I can't go out and look at the situation on the turbo's oil return route. But, If it is via a return line/tube of some reasonable length, an (oil) temp guage's sending unit might be hose-clamped along side the tube. Temperature reading via conduction. Apply a good insulation wrap so as not to pick up another source of heat. A person would have to look around at the various guages to find an element that would lend itself to this thought, half-baked as it may be, but it could be done. It may not read as quickly as having the element/sending unit installed via a thermowell, but you would at least have a clue as to the oil's temp...

CWB

Or perhaps a regular pyro gauge attached directly to the hot side of the housing. Neither pre-nor post turbo EGT, but actual turbo CASE temp.

Will JB weld handle 1600?

My aftermarket turbos on my twin turbo Z actually had the tap for the pyro directly on the turbo inlet. My only concern with putting a probe there is if you get probe failure it is just about gaurenteed to be injested.

As far as cool down, I think most of us should be worried about coking as that is what is going to kill bearings. Even in the Helicopters I fly our #1 concern at shutdown is to ensure the EGTs for the engines are below a certain temp and as soon as we shut them down we monitor them to ensure they dont climb back up (tailwind blowing hot exhaust). We just dont want to cook any oil onto the bearing surfaces and shuting down to hot will do that.