How long to idle in the cold?

[opjohnny]

I have no gauges as of yet and I give it the times as per the owners manual during the summer. In the winter when it is 0 deg F or 30 deg F, is the time necessary when your not pulling a load? I hate wasting the fuel on idle time when it is 20 deg F out.



Thanks, John

 

[B.G. Smith]

If you are running 70mph and stop on the side of the road, yes, the temp. will be a little high to shut off but when the temp. is below 30 deg. F, and you are doing stop and go or slow driving the temp. will be below 300 deg. F. And of course. hte temps. go down faster when it is that cold. bg

 

[rbattelle]

Just to clarify, John are you asking about the idle time when you first start the engine or the idle time to let the turbo cool down?



-Ryan

 

[opjohnny]

Sorry about that, I was talking about the cool down time.

 

[rbattelle]

Although what B. G. mentions would seem logical, I've noticed that ambient temperature has at best a tenuous relationship to cooldown time.



In any case, I can't say I've ever managed to stop my truck with the post-turbo EGT above 300. Just the act of slowing down and coming to a stop is enough to get the EGT down below 300 post turbo. Usually I'm at 200 by the time I complete a stop, so I just wait several seconds and then shut down. My point is, unless your pulling off the highway from 80 mph in a panic stop, you can be sure your EGT is below the 300-degree safe temperature.



Heck, cruising down the highway at 65 mph on level ground my EGT is rock-solid at 300.



I hope that helps a bit...



-Ryan

 

[Papa Delta]

rbattelle

Mine isn't! I have an 04. 5 with blah blah blah (check sig) and running down the Expressway at 65 I'm in the 500 degree range. I never see exactly 200 even from a cold start. I always wait until I get to less than 300 deg before turning my engine off. Is your probe pre turbo?

 

[rbattelle]

Mine isn't! I have an 04. 5 with blah blah blah (check sig) and running down the Expressway at 65 I'm in the 500 degree range. I never see exactly 200 even from a cold start. I always wait until I get to less than 300 deg before turning my engine off. Is your probe pre turbo?

No, my probe is POST turbo.

 

[B.G. Smith]

Although what B. G. mentions would seem logical, I've noticed that ambient temperature has at best a tenuous relationship to cooldown time.



In any case, I can't say I've ever managed to stop my truck with the post-turbo EGT above 300. Just the act of slowing down and coming to a stop is enough to get the EGT down below 300 post turbo. Usually I'm at 200 by the time I complete a stop, so I just wait several seconds and then shut down. My point is, unless your pulling off the highway from 80 mph in a panic stop, you can be sure your EGT is below the 300-degree safe temperature.



Heck, cruising down the highway at 65 mph on level ground my EGT is rock-solid at 300.



-Ryan[/QUOTEr]

Just how far "post" is your probe? Must be in the tail pipe extension. You might need to check the accuracy of your EGT gage setup? bg

 

[rbattelle]

Just how far "post" is your probe? Must be in the tail pipe extension. You might need to check the accuracy of your EGT gage setup? bg

It's in the elbow, about 2. 5 inches downstream of the turbine. Penetrates beyond the internal radius of the pipe. I believe it reads accurately in that location.



On Edit: highest temps I've ever seen were around 800 give or take 50. I have a gauge that's color coded and calibrated for post-turbo installation. Everything's green up to 900 degrees. Link.



-Ryan

 

[B.G. Smith]

I like the looks of that gage. My probe is in the elbow too, I get above 400 driving at hwy. speeds. Runs 500/600 when towing in flatlands. Mine cools off pretty fast when it is 400 or below but when towing it takes at least as long as the manual recommends or longer. bg

 

[Kennywould]

It's in the elbow, about 2. 5 inches downstream of the turbine. Penetrates beyond the internal radius of the pipe. I believe it reads accurately in that location.



On Edit: highest temps I've ever seen were around 800 give or take 50. I have a gauge that's color coded and calibrated for post-turbo installation. Everything's green up to 900 degrees. Link.



-Ryan

Ryan

Quick question since pre and post install is always an issue in the forums, if there is about 300 deg difference between the two, I usually shut down at 250 - 300 at pre turbo would it not be much less at post turbo? I'm not jerking you, just asking because that +/- 300 always bothered me!

 

[rbattelle]

Ryan

Quick question since pre and post install is always an issue in the forums, if there is about 300 deg difference between the two, I usually shut down at 250 - 300 at pre turbo would it not be much less at post turbo? I'm not jerking you, just asking because that +/- 300 always bothered me!

What I'm about to say is my educated opinion... take it or leave it.



It's important to remember that there can be up to a 300 degree difference between pre and post measurements, but that's only going to happen when you're drawing a lot of energy out of the exhaust stream, hence reducing its temperature significantly. So let's say you're running WOT up a steep grade towing 15k. Your pre-turbo EGTs might be as high as 1100 degrees, but since you're pulling a ton of energy out of the exhaust flow to generate 25 lb of boost, you're dropping the temperature post-turbo down to maybe 800 degrees (maybe less).



At idle, the turbo is making very little boost, if any at all. You're really not using any of the energy in the exhaust stream, so the difference between the pre and post turbo temperatures will be very small. I don't yet have a pre-turbo gauge, but I'd guess the difference could be as little as 50 degrees (hotter on the pre-turbo side).



Always remember: temperature is defined as the average kinetic energy of the molecules in a substance. Add energy, temperature goes up. Subtract energy (as with a machine like a turbine), temperature goes down.



What does all this mean? It means if you're sitting there idling and your pre-turbo gauge indicates 300 degrees, your post-turbo temperature is most likely 250 or less. Give it a few seconds (maybe 10?) to be sure the turbo case temperature has dropped, and shut 'er down.



-Ryan

 

[bpenrod]

I had read a good article on a large truck site where the author stated the difference between pre and post turbo temps was related to boost while under load. He claimed the turbo used 10* to make 1# of boost. If that is correct the 25# boost example above would cool the exhaust at least 250* at the turbo exit. I'm not sure how fast the exhaust stream cools down as it travels the pipe but by that time it does not really matter. Anyway, just passing along something I read... ...

 

[LightmanE300]

OPJohnny - I have my probe pre-turbo as most folks do - and shut off once I get to or below 300F. Even if I'm putting around town, when I come to a stop light and am in drive, the temp hovers around 400 something. Regardless of how long or hard I drive, I have to let it idle for 15-30 seconds to get it below 300.

 

[PKnoerzer]

I have the same set up as Lightman, and see the same temperatures. Cooling it down to 300 degrees pre-turbo is adequate isn't it? I normally shut down after the needle drops under the 300 mark.

 

[rbattelle]

I have the same set up as Lightman, and see the same temperatures. Cooling it down to 300 degrees pre-turbo is adequate isn't it? I normally shut down after the needle drops under the 300 mark.

As I mentioned earlier:

What does all this mean? It means if you're sitting there idling and your pre-turbo gauge indicates 300 degrees, your post-turbo temperature is most likely 250 or less. Give it a few seconds (maybe 10?) to be sure the turbo case temperature has dropped, and shut 'er down.

 

[Kennywould]

What I'm about to say is my educated opinion... take it or leave it. -Ryan

Ryan

Thanks, I thought about that afterwards and I will accept your opnion on this one, makes sense!

 

[WStoops]

My pre-turbo temps run 500 to 600 at 65 mph. Hard pull up a steep hill, unloaded will get to 1500 if I don't let up on it. It idles around 300 degrees.

 

[CJEliassen]

I think you guys are missing something when it comes to cool down temps. Your probe is measuring the exhaust GAS temperatures. If you are running at WOT or crusing along at 65 and come to a stop, the EGT's will be the same at idle. What is different is the heat in the turbine. The turbine might be glowing red yet your EGT's are 200. So, in order words, you can not use an EGT probe to determine when your turbine is cool.

 

[rbattelle]

The turbine might be glowing red yet your EGT's are 200. So, in order words, you can not use an EGT probe to determine when your turbine is cool.

I respectfully disagree because this assumes no heat transfer between the turbine and the exhaust stream. Given the very low specific heat of air I expect the exhaust gas temperature to approximate the turbine temperature within just a few degrees.



Hey Kennywould - I'm a Steelers fan too, doesn't that mean all my opinions are automatically correct?



-Ryan