I have a 2006 F250 6.0L that we bought primarily to tow our 5<SUP>th</SUP> wheel camper and to serve as our primary vehicle when at camping destinations. I have no plans to chip or tune the engine and I installed a EGT gauge post turbo to monitor the EGT during cool down.

I have searched the FAQs and posts for information on cool off time and temperature and it seems that the conventional wisdom is to allow it to run for several minutes or until the post turbo temperature cools to 300 degrees. After towing that seems like very good advice, but is it necessary for every day driving? Case in point: today I drove the truck about 10 miles and the post turbo EGT got to about 600 degrees. When I pulled into the driveway it was about 500. It took about 5 minutes to cool to 300 degree. That seems a bit much for a quick run to the mall. Idling for 5 minutes every stop will get real old real fast. So my question is how much cool down is really necessary for day to day to-the-mall sort of driving?

 

I have mine set to 358 deg and it rarely runs for more than a few seconds. A number of others in a recent thread have reported setting theirs to 400 deg.

Hint, turn off the AC about 30 seconds prior to pulling into your parking place to remove that extra load from the motor. It will cool down just that much faster.

 

I agree with the above. I normally shut mine down at when it goes below 400. This is pre turbo. To get to 400 pre turbo only takes a few seconds like Daryl said.

 

I agree that turning down AC helps alot. In these AZ summer months I can't get the EGT below 400 at idle.

 

I have a possibly related question. On my 05 F350 6.0 it has two factory temp gauges. One is obviously engine temp but the gauge above is that egt or trans temp?

 

If it has a "picture" of a gear with a thermometer in it , it's tranny temp. I don't think any of the Fords monitor EGT at all.

 

transmission

 

Good question. I think this relates to the pre or post turbo thermocouple location debate. Which location best approximates the temperature of the turbine in the turbo? I think the best location of the thermocouple would be in the exhaust housing of the turbo, so you can measure the actual maximum air temp that the turbine is subjected to.

The Pre turbo location lets you measure the max exhaust temp coming out of the cylinders if the tip of the thermocouple is in the center of the exhaust flow. In this location, you can safe guard against melting your pistons and what temperatures you may be subjecting the turbine to. But in the pre turbo location the thermocouple will also cool off faster than it will in the post turbo location.

The post turbo location allows you to get a better idea of what your trubo's turbine is actually "seeing," but doesn't really give any information about what is happening upstream. The turbine uses exhaust velocity and heat to turn the compressor; which in turn generates pressure and heat.

The problem lies in trying to find one easy location or temperature to determine when it is best to shut off your truck. There are too many variables to give a simple answer. You have the exhaust gas temp, the compressor inlet/outlet temp, the turbine inlet/outlet temp, the oil temp, thermal conductivities and mass of all the metals, oil, and air (at changing temperatures and densities), plus all the different flow rates of the air and oil, plus take into account for the reduced cooling/heating capability of the air as it passes around the blades of the compressor and turbine due to flow separation,...etc.

If the exhaust gas temp in the exhaust manifold (center of tube), is 400 °F, I think it would be easy to still have the turbine temp at 600+ °F. It is going to take time to pull the heat out of the turbine mass. But you have a hot side (the turbine) and a cold side (the compressor), plus the engine oil cooling the bearing. So the compressor and oil are acting as heat sinks, wicking away the heat from the turbine.

So how cool does the turbine need to be, when you shut off the truck, that the heat that is still in the turbo shaft doesn't coke the oil? I don't know, I have never done the flow simulations to find out. A five minute idle might be a bit conservative, but a one minute idle, may not be long enough. You can always run a full synthetic oil to increase the smoke temp of the oil and reduce the chance of coking the bearing.

But I think a 400 °F post turbo temp would be good. At least then you know that the turbine can't be much hotter than that.

 

"MYTH #7
You have to let a turbo-diesel idle for two minutes before you shut it off.

FACT
This is a current myth that has a basis of fact stemming from many years ago. It also has a kernel of truth regarding today’s turbocharged gasoline engines that operate at higher peak exhaust temperatures than turbo-diesels. In the early days of turbochargers, the turbo shaft was supported by a babbitt bearing that could seize, or even melt, if the engine was shut off immediately after sustained boost conditions where the turbocharger would “heat soak”. A two minute cool down at idle allowed the turbocharger to dissipate any remaining spinning inertia, and the oil circulation cooled the bearing and prevented oil “coking” in the bearing area. Turbochargers haven’t used babbitt bearings for over 30 years, and today’s oils resist coking. Synthetic oils won’t coke, period. With a turbocharged gas engine, it’s still good insurance to let the engine idle for 30 seconds to a minute to allow the turbo or turbos to dissipate any inertia and to cool the bearing area to prevent oil coking, especially if the engine has been worked hard just prior to shut-down. Of course, using quality synthetic oil eliminates this potential coking problem.

Today’s turbo-diesels are a different story. There is really no reason to “cool down” a turbo-diesel these days, but you won’t hurt anything by doing it either. You can still find people who swear you have to do it, but the myth is fading. Maybe they just like to sit and listen to the radio."

From
http://bankspower.com/tech_TD-fact-Fiction.cfm

 

Interesting that Ford buys into this myth. Quote form the '06 Diesel owners manual "It is recommended that a hot engine be allowed to operate at low idle for about 7 - 10 minutes which would allow sufficient time for the turbocharged engine to cool down."

 

I let mine cool down when i drive it everyday. It idles from the point i hit the garage floor to the time its pulled completely in.

I dont think its really neccesary.

 

I let mine cool down...for at least 5 - 10 seconds....

 

There were 2 theories in letting a turbo (turbine) cool down slowly. The babbit bearings was one reason, the other was the rotor and shaft itself bowing. (as short and vastly supported our little turbos are probably never have a problem bowing a wheel or shaft) All large turbines that have been upgraded to tilt pad bearings from the old spherical bearings still allow the shaft to roll for several hours to keep it from bowing. (they are very large and take a long time to cool down). On medium to large stationary engines, that use turbos similar to our application and size, they come from the factory with a cool down cycle programmed and post lube to the turbo as well, if either is modified or shortened in length of time the manufacturer can void the warranty. If it was not necessarry, then why do all the engine manufacturers still do it? (Cat, Cummins, MAN, Waukesha, Detroit) Food for thought.

Ryan

 

He was refering to normal city driving. The way I would translate the Ford owners manual that is stated: It would have me thinking after a long drive on a freeway trip in hot weather, towing etc.

 

Don't get me wrong, right now I take time to shut down. I am just trying to get to the truth.
I would like to hear from a Diesel Mechanic on how many turbos they repair due to this problem?
Fletch