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Old 03-20-2013, 02:05 PM   #1
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Diesel Cooldown

I know that you should let a hot engine idle to cool down before shutting it off. I've always done it by the seat of my pants. If it seems hot, I idle it for a minute or two then shut it off. When climbing a long grade I usually stop and let it rest if transmission temp goes over 220 or oil goes over 225.

But how hot is too HOT?

Should I watch coolant, oil, trans or exhaust temp and how low should it go before I can shut down?

We're talking about a 7.3 here if that matters.
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Old 03-20-2013, 02:26 PM   #2
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Re: Diesel Cooldown

I use EGTs as my guide on when to shut down.

For my Exursion (7.3L), I never shut down the engine when above 400 degrees, and I try to shut down when its at 350 or below. That's with the probe mounted pre-turbo.


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Old 03-20-2013, 03:06 PM   #3
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Diesel Cooldown

I've always been told it was important, mostly for exhaust manifolds and related parts. At least that's what I was told on the 460s I've had. Probably wise on the diesels too to cool the turbos down a bit.
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Old 03-20-2013, 03:52 PM   #4
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Re: Diesel Cooldown

On the 6.0 psd it's all about coking the turbo and egr valve. It can take a couple of minutes or more for mine to cool down after a long pull.

A pyrometer can be added to the The Edge Insight which has an automatic idle/shut-off option.
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Old 03-21-2013, 07:27 AM   #5
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Re: Diesel Cooldown

My post turbo idle temp is slightly below 500*. My engine running at slow speeds (below 25 MPH) are about 550-650*. What I've read is that even an easy drive is cool enough for shutdown so I figure if I hit 500* I'm OK. Probably depends on where the temp is taken from. I have a Autometer aftermarket gauge on my van and have never compared it to the computers reading.
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Old 03-21-2013, 08:24 AM   #6
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Re: Diesel Cooldown

Quote:
Originally Posted by daveb
My post turbo idle temp is slightly below 500*. My engine running at slow speeds (below 25 MPH) are about 550-650*. What I've read is that even an easy drive is cool enough for shutdown so I figure if I hit 500* I'm OK. Probably depends on where the temp is taken from. I have a Autometer aftermarket gauge on my van and have never compared it to the computers reading.
I think there's as much as a 200 degree difference depending on whether the thermocouple for the pyro is mounted pre- or post-turbo. Pre-turbo is affected by the temp of the exhaust manifold.

Mine is located post-turbo and my readings are similar to yours. I turn off when it's 450-500.
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Old 03-21-2013, 12:33 PM   #7
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Re: Diesel Cooldown

Thanks to all for the good info. My EGT is pre turbo so I'll be looking to get it under 400 before shutting down.

Yesterday was the first time I've driven a vehicle with an EGT. I was very surprised to see how fast it responds. You could almost use it as a proxy horsepower gauge.

After it was warmed up it read about 350 at idle, 700 at 60mph on the flat, jumps to 1100 climbing a hill and down to 400 gliding back down the hill. This was on a cool wet day. The temp changes happened over only a 100yds or so.
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Old 03-21-2013, 09:47 PM   #8
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Re: Diesel Cooldown

Hey Bill, I kinda lied a bit. Oops. Tonight I noticed the markings on my gauge isn't 500 but 400 so I do Idle down to 400 on a regular basis. Sure there are times where I shut down a bit hotter yet I still stand by what I've read, 500 is a good point.
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Old 03-21-2013, 11:01 PM   #9
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Diesel Cooldown

I know this is going to sound crazy, but you might consider taking a glance at your owner's manual. Mine is an '09 6.0L. It's been a while since I read it, but if memory serves, there is a whole section on cooling down the turbo.
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Old 03-21-2013, 11:05 PM   #10
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Re: Diesel Cooldown

On my 7.3 I try and wait until the Edge is showing under 400 for EGTs, and preferably 350 or below. I have the alarm set at 1250 for EGTs but it rarely goes above 1150 even on hills and when I see it getting near that I downshift or slow down. The exhaust wrap from turbo back past the tranny really helped lower my EGTs.
I also will let my tranny cool down if it is up over 200 or so. I have an aftermarket cooler underneath the van that has a fan so I turn that on if needed as well.
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