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Old 08-11-2014, 04:52 AM   #1
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Turbo cool time

Just a basic poll... on my 05 cummins, I always let it run after pulling to allow the turbo to cool with oil flow. I don't have an EGG gauge yet, but just let her idle as I get the TT set up and hitch off. A buddy of mine has an 06 Duramax and will he pull his 10 TT hard and shut it off immediately. .. Do the duramax ' s not recommend or need this cool down period?

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Old 08-11-2014, 05:47 AM   #2
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There are lots of opinions on this on here and diesel forums. I like your idea of just a little amount of idle, but not enough to bother anyone too much.
I let my EGTs get to around 400*F, then shut off. But, I also don't come right off the interstate pulling 10lbs of boost for an hour and shut it right in the first place either.

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Old 08-11-2014, 07:34 AM   #3
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Originally Posted by chertz View Post
Just a basic poll... on my 05 cummins, I always let it run after pulling to allow the turbo to cool with oil flow. I don't have an EGG gauge yet, but just let her idle as I get the TT set up and hitch off. A buddy of mine has an 06 Duramax and will he pull his 10 TT hard and shut it off immediately. .. Do the duramax ' s not recommend or need this cool down period?
I have a 08 6.7L Cummins with gages. MY EGT gage will show between 600 too 800 F as I exit the interstate and enter the rest area. By the time I get to a stop in the truck parking area my EGT gage is showing 350 to 400F depending on ambient air temps. I will shut the engine off at 400 F on the EGT gage.

When I was stock I could idle all day long and the truck would never get below 400F on the EGT gage with the current emission equipment on the truck. So this is the temp I will shut off at now.

I would not tow any trailer without at least a boost and EGT gage on the truck. These are not hard to install and Geno’s Garage sells factory match gages for your truck with assembly instructions. See the attached link.


Jim W.
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Old 08-11-2014, 07:51 AM   #4
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No need to worry about most diesel turbos when driving normally, even towing. But when you get the engine very hot and the turbo red hot, such as dragging a heavy trailer to the top of a mountain pass, or dragging a heavy trailer at 80 MPH on the interstate at 1,000 to 1,200 EGT, then shutting down the engine before the turbo bearings have time to cool down some can kill the turbo.

When the engine dies, the oil stops circulating inside the turbo bearings. The red-hot bearings then cook the oil in the bearings into coke.

If you shut down a very hot diesel turbo without a cool-down period to allow the turbo bearings to cool down at least a little, then the result could be oil coking. Coked oil is like sandpaper. As the oil cools down that "sand" is in your bearings, so the next time you crank the engine your turbo bearings get a good sandpaper effect.

Two preventative measures: 1] use only the dino motor with the specs required by your engine, and maintain fresh motor oil in your engine. Used oil analysis (UOA) is the best way to be sure you're changing the oil often enough for your use of your engine. Synthetic motor oil won't hurt anything, but not necessary to protect your turbo bearings provided you also do 2]. And 2] is to let the hot engine idle until the pre-turbo exhaust gas temp (EGT) drops down to normal idle temp, which on mine was around 300. If you don't have a pyrometer to give you EGT, then install one. Without a pyrometer, you have to guess at how long it takes for the turbo to cool down enough.

I had a good pyrometer, but I hated twiddling my thumbs while I waited for the EGT to fall down to the safe level, so I also installed an ISSPRO Turbo Temp Monitor (TTM). That's a black box that won't allow the engine to die until the EGT falls to a safe level. EGT doesn't tell you the temp of the turbo bearings, but the experts have determined that you can use EGT to estimate a safe shut-down temp. With the TTM, you don't even need a pyrometer but you do need the sender (thermocouple) that a pyrometer uses to obtain EGT.

On mine the time required for the TTM to kill the engine varied from a few seconds to a few minutes, depending on how hard the engine was working before I turned off the key. After I turned off the key and put the keys in my pocket, the engine continued running until the pyrometer showed about 300, then the engine would die. I had the keys in my pocket so the steering wheel was locked and the tranny would not shift out of park, so no worry about somebody stealing the truck while I was in the 7-11 with the engine idling and cooling down.

Worked great for me for the 12 years and 200,000 miles I drove that turbo diesel pickup, with no worries about coking the turbo bearings.
ISSPRO R4130 Turbo Temp Monitor
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 3.5L EcoBoost SuperCrew.
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Old 08-13-2014, 01:29 PM   #5
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As a former mechanic for the Marines for the Amphibious Assault Vehicles (tracked amphibious personnel carriers with 903ci turbo diesel motors) - we were taught to cool any motor that had been run hard by idling it for 6 minutes or if we needed to cool it quicker, run at a high idle (1200rpm) for 2 minutes with no load - meaning neutral. If 2 minutes could not be done, 30 seconds at 1200rpm with no load was minimum. They said our lives may one day depend on these motors running and hot shut downs kill the longevity of them. Like others have stated, it allows heat to be removed by the cooling system and the oil won't coke in the turbo as easily. The no load/high idle circulates coolant, oil, other fluids, and lower EGTs from no load being on the motor cools the turbo and exhaust.

Having a Dodge 5.9 CTD I try not to shut down hot after towing. I idle down highway off ramps and go slow to any fuel stations to allow cooling. I use the 1200rpm no load/high idle if I feel it hasn't cooled enough, to remove more heat. Secondary roads usually present no heat problems. I watch my temp gauges go down before shutting down to fuel. Where I live, the road is long and slow enough to cool my truck and I back in my yard and let it idle while unhooking. I also let it idle after getting to a CG while checking in and unhooking.
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