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turbo cool down #5218638 09/21/19 09:04 AM
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mobilaltima Offline OP
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I was always taught when driving a diesel vehicle to always let the EGTS come down and let the truck idle for a few minutes after a hard run or when towing. I've always adhered to this . F250 in my sig, last night I got on the road(not towing anything), quickly got it up to 80 mph then turned in the median, got it up to 50 mph before pulling up to a roadside taco stand to order food. There were people ordering so out of courtesy I let it idle for about 30 seconds before shutting it off(engine is pretty loud). I know Im probably worrying for nothing but could that quick run to 80 mph coupled with the quick shutdown have damaged the bearings in the turbo? Truck is stock besides a straight piped exhaust and I'm running Supertech 15W40.


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: turbo cool down [Re: mobilaltima] #5218642 09/21/19 09:13 AM
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WondrousBread Offline
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I don't know much about diesels so someone else may have better input.

However, I believe the reasoning for idling before shut-off is twofold.

First, you give the engine a chance to heat up and cool down evenly, as some parts of the engine generate more heat than others. Since different parts are expanding and contracting, it's probably good for wear.

Secondly, when parts of the turbocharger are hot they are hard on oil. Oil is flowing when the engine is running, so no big deal. But after a hard run the oil in the turbo doesn't move as much (other than slowly draining) so the hot spots have a chance to bake the oil much hotter than normal. The term for this is "coking".

It's a good practice to let the engine idle for a bit after a hard run or towing, but if you only did it one time I wouldn't worry. Don't make a habit of it, but doing it a few times is probably inconsequential.

Re: turbo cool down [Re: mobilaltima] #5218643 09/21/19 09:14 AM
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demarpaint Offline
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This has been discussed before, you'll hear the engine was designed to be shut off w/o an idling period. Then you'll hear it is best to idle it for 30 seconds before turning it off. I agree with that. It is just like the drop the factory fill early on a new car debates that come up from time to time. There are two sides dug in deep on both topics.


God Bless Our Troops

Re: turbo cool down [Re: mobilaltima] #5218644 09/21/19 09:15 AM
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billt460 Offline
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Question for anyone who knows for certain..... Do turbochargers on diesel engines run cooler than turbos on gasoline engines?

Re: turbo cool down [Re: mobilaltima] #5218653 09/21/19 09:26 AM
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CT8 Online Content
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The oil doesn't matter. Get a pyrometer to see the temps .When my wife bought her F250 7.3 back in 2002 the first thing I did was put a pyrometer in it. Summit auto parts sells them. The problem would be is when you shut down a hot turbo the oil can cook from the heat and the head can be well above any base oils flash points. I didn't drive the truck enough to remember the operation and temps in the 16 year we owned the vehicle.


2015 F150 2.7
2018 F350 6.2
Re: turbo cool down [Re: demarpaint] #5218658 09/21/19 09:29 AM
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CT8 Online Content
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Originally Posted by demarpaint
This has been discussed before, you'll hear the engine was designed to be shut off w/o an idling period. Then you'll hear it is best to idle it for 30 seconds before turning it off. I agree with that. It is just like the drop the factory fill early on a new car debates that come up from time to time. There are two sides dug in deep on both topics.

This website has replies of preconceived notions and occasionally facts. The hart part is discerning between the two.


2015 F150 2.7
2018 F350 6.2
Re: turbo cool down [Re: billt460] #5218659 09/21/19 09:30 AM
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CT8 Online Content
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double click.

Last edited by CT8; 09/21/19 09:34 AM.

2015 F150 2.7
2018 F350 6.2
Re: turbo cool down [Re: CT8] #5218669 09/21/19 09:44 AM
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demarpaint Offline
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Originally Posted by CT8
Originally Posted by demarpaint
This has been discussed before, you'll hear the engine was designed to be shut off w/o an idling period. Then you'll hear it is best to idle it for 30 seconds before turning it off. I agree with that. It is just like the drop the factory fill early on a new car debates that come up from time to time. There are two sides dug in deep on both topics.

This website has replies of preconceived notions and occasionally facts. The hart part is discerning between the two.

Exactly. Which is why it is important to do your own homework, and avoid believing blanket statements to be Gospel.


God Bless Our Troops

Re: turbo cool down [Re: mobilaltima] #5218673 09/21/19 09:47 AM
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wensteph Offline
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I've always waited a minute or so cool down from highway runs and don't do anything special for town driving.

Re: turbo cool down [Re: mobilaltima] #5218675 09/21/19 09:48 AM
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JLTD Offline
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What does your owner's manual say? Depends on the design.


I use the overseas manual to choose my viscosity.

Using AMSOIL

Hers: 2008 Jeep Liberty 154k, SS 5w30/Amsoil

His: 2015 4Runner 60k, SS 5w20/Amsoil

Re: turbo cool down [Re: mobilaltima] #5218702 09/21/19 10:13 AM
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maxdustington Online Content
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Water cooled turbos and auxiliary water pumps exist. It's not 1993 anymore, you don't need a turbo timer on your Eagle Talon TSi.


97 GMC RCLB K2500LD L30/4L60
Re: turbo cool down [Re: maxdustington] #5218749 09/21/19 10:56 AM
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Originally Posted by maxdustington
Water cooled turbos and auxiliary water pumps exist. It's not 1993 anymore, you don't need a turbo timer on your Eagle Talon TSi.


1. No matter how hard I drive the car, there's always a period of time where I'm not hard on the car before an "immediate" shutdown. What I mean, is that I've never driven at full-boost and then power-slid into a parking spot before immediately shutting the engine off; there's ALWAYS some engine braking while you slow down, some low-speed driving while you find a spot, etc.

2.
Originally Posted by maxdustington
Water cooled turbos and auxiliary water pumps exist. It's not 1993 anymore, you don't need a turbo timer on your Eagle Talon TSi.


All of my recent turbo Subies have had water-cooled turbos. The turbo (heat source) is lower than the radiator or secondary reservoir (heat sink), allowing for natural circulation of the coolant through the system, including the turbo, until the driving head (differential temperature between the coolant passing through the turbo) and that of the radiator is insufficient to overcome the differential height (gravity).


14 Forester XT Touring FA20DIT (Cobb Stage 1)
Castrol Magnatec 5W-30 D1G2 + FU filter (72,320mi, 8/24/19)
15 Legacy Premium FB25
Magnatec 5W-20 + FU filter (47,300mi, 5/11/19)
Re: turbo cool down [Re: mobilaltima] #5218827 09/21/19 12:36 PM
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edyvw Offline
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Originally Posted by mobilaltima
I was always taught when driving a diesel vehicle to always let the EGTS come down and let the truck idle for a few minutes after a hard run or when towing. I've always adhered to this . F250 in my sig, last night I got on the road(not towing anything), quickly got it up to 80 mph then turned in the median, got it up to 50 mph before pulling up to a roadside taco stand to order food. There were people ordering so out of courtesy I let it idle for about 30 seconds before shutting it off(engine is pretty loud). I know Im probably worrying for nothing but could that quick run to 80 mph coupled with the quick shutdown have damaged the bearings in the turbo? Truck is stock besides a straight piped exhaust and I'm running Supertech 15W40.

I owned BMW 525d E61 in Europe and made 425k km on it. I would do 120-130mph runs, get off HWY, drive normally 2-3 miles and turned it off. In those 2-3 miles, according to OBD I had hooked up, coolant and oil temps. go down to normal.
When I was doing 80-100mph with that car I never bothered cooling it off. And at 425k km did not use drop of oil, and could still top off at 145mph.
I would say, get more Taco's smile

Last edited by edyvw; 09/21/19 12:37 PM.

15' Toyota Sienna AWD (Mobil1 5W30 EP+OEM filter).
11' VW Tiguan 2.0T (Castrol 0W40+MANN filter)
Re: turbo cool down [Re: mobilaltima] #5218851 09/21/19 01:03 PM
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Pisto Offline
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Hey everybody. I am writing for the first time on this great forum from far away Finland. I have followed with great interest what is written here. I could try to answer that question. Let's start with the diesel and gasoline engine efficiency. The efficiency of the diesel engine is better because the combustion process lasts longer on the piston than on the gasoline engine. Thus, thermal energy is converted into longer kinetic energy than in a gasoline engine. As a result, the exhaust fumes are cooler in the diesel engine than in the gasoline engine. It is also worth mentioning that I am following this forum, since petrochemistry in particular is of great interest and there are good answers here.

Re: turbo cool down [Re: billt460] #5218858 09/21/19 01:07 PM
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A_Harman Offline
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Originally Posted by billt460
Question for anyone who knows for certain..... Do turbochargers on diesel engines run cooler than turbos on gasoline engines?


Yes, they do. Hundreds of degrees (F) cooler at full power.


1985 Z51 Corvette track car
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel
1972 GMC 1500 shortbed project truck
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