Cooling Off Idle

[Barrman]

I was taught from the time I first started messing with mechanical items that a turbo needs to idle for about 5 minutes after it has been run to let it cool down and get all the hot oil out of it. To not do this would result in a blocked oil line which will lead to a very expensive turbo purchase plus whatever engine parts got caught up in the distruction.

All these years later I have a turbo on my A2. I also live at the end of a 1/2 mile long dirt road. I have gotten into the habit of putting the truck in low 2nd and just letting it idle down the road with my feet flat on the floor. I can actually watch the temp gauge go down to 160 and stay there during that long idle drive.

Here is my question. If I am not using the throttle, the manifold pressure is not getting raised which means the turbo is not making heat. So, for engine long life, is what I am doing the same as the truck sitting still at idle?

Thanks.

 

[littlebob]

Kinda wondered the same thing. I would much rather let it idle around the neighborhood whil it was cooling down, probably get to meet more neighbors.
littlebob

 

[WillWagner]

I f you are just buzzing around town in stop sign/light to stop whatever, no need to do the 5 min. idle thing. If you are out on the highway, doing close to top speed or had a load on it and pull up to your stop, definatley do the idle b-4 shut down thing.

 

[m16ty]

Even with low engine coolant temps you can still have high EGT. That's what will cook your turbo. That being said, I often do the same with my road tractors and you can watch the pyro and by just taking it easy for a little bit right before shutdown will cool it off just as much as letting it idle for 5 minutes.

 

[Jake0147]

Turbos don't make heat, they catch a lot of it from the engine.

You've got exhaust gas on the turbine wheel and housing that might be a thousand degrees when it's working. (Obviously that varies by vehicle and settings). So if the turbine is at a thousand degrees, and you shut it off, all that heat will "soak" into the guts of the turbo and raise the temperature of the bearings/bushings that are no longer recieving fresh cool oil. That'll end up "baking" the remaining oil on/in them into sludge. That of course destroys the bearings by blocking oil flow and/or just by it's very presence. It also is pretty hard on the seals. The run time gives the heat a chance to equalize and begin to dissipate via the moving oil and directly to the air. Thus when you shut the engine off and the spike of heat hits the center of the turbo, it isn't such an extreme that it causes damage to the oil.
The five minute run time is not because five minutes exactly is what's required, it's because it's a "safe" number to throw out to make a standard.
The five to ten minutes of driving prior to the shutdown routine is a big factor in what the shutdown routine needs to be. If you're coming off of a freeway where it's wide open for an hour, and then to your dirt road, it's a big issue and you'll want to make sure it's got at least it's full five minutes even if you count the time idling along the dirt road towards the total idle time. If you're coming from lower speed secondary roads where the exhaust wasn't really that hot (relatively) to begin with, then it's probably just fine to idle in and shut it off.

 

[M543A2]

I have to take exception to the statement that turbos do not make heat. The work the compressor side does in compressing the air definitely builds heat in the charge air to the motor. Charge air can reach temps upward of 300 degrees from the flogging of the turbo compressor vanes. Think about large air compressors in factories. They build a lot of heat in the outgoing compressed air. Many have coolers on them to reduce the air temperature. Even on your personal shop air compressor you will find the output line from the compressor head to the tank gets warm. Many diesel turbo trucks also have an intercooler, like a radiator in the charge air tube between the turbo and the motor to cool the charge, which means more horsepower because the charge air is denser if it is cooler, which results in more air available to burn the fuel. I do agree totally with the statements about the heat of the exhaust and its affects on the turbo if not properly cooled after a hard run. Idling along in a low gear will definitely help cool the turbo.
Regards Marti
Regards Marti

 

[deess]

anybody ever thought of making a intercooler for a deuce ?

 

[m16ty]

anybody ever thought of making a intercooler for a deuce ?

Yes I have. The problem is finding a place to put it without alot of front end modification.

The deuce already has a water cooled intake in it's stock form. I've thought about isolating the intake cooler from the engine coolant and use a heat exchanger to drop the intake temp more than engine coolant temp but you still run into space issues.

 

[WillWagner]

anybody ever thought of making a intercooler for a deuce ?

It kinda already does...an air to water intake manifold... aftercooling. Since these engines run on the cool side...180 or there about, the intake manifold will do a good job of keeping the charged air at a fairly constant temp close to the coolant temp of the engine once up to operating temp. Not nearly as efficent as a charge air cooled engine like the modern engines...except for Cat, they went kinda backward with the compound turbo and air to water cooling

 

[Djfreema]

On my last truck, I had an extra pyrometer probe that I installed in the elbow coming out of the turbo before entering the intake manifold. I had the probe hooked up to my digital multimeter that had a temperature setting. I measured over 200 degrees in the charge air temperature when going up the grapevine flat towing another duece while the coolant temperature was between 180-200.

 

[Tackettr]

Here is my short answer to the original post. As long as RPM is below 1000 for 5 mins, your good in my book. Says so on the warning decal. Kinda if you put them both together.

Also, I know for a fact that helicopter turbine engines require a cool down period also, however not 5 min. usually, 2-3 min. This has always been briefed to me as a period to allow the turbine temps to stabilize to prevent cracking and warping since they have tight tolerances. So on helicopters with wheels like the blackhawk, if you are below a certain power setting like when taxiing (rolling) to parking you are allowed to count that as part of your cool-down period. I can't see why it wouldn't apply to the deuce.

PS: I think the 5 mins has alot of safety margin factored in, but that just me. However, I still do it.

 

[andyindy]

I agree with most every thing mentioned, but I was always told that also, the idle time at shut down was to let the turbo run down from it's high RPM's and to have a supply of oil to the bearings during rundown. We have a older D8 K at work and even after a 5-10 minute idle, you can still hear the turbo slowing down after you shut it off.( If you had your ear plugs in, WHAT, HUH, YOU SAY SUMPTIN?)

 

[randyscycle]

Tim, I think you're fine. I watch my pyro after a haul into town of 15 miles at 50+ on the highway, and its around 400F at idle until I let it sit for several minutes then it comes down to around 275F.

If I just backroad it around the area, the idle temps come down very quickly to 275-300F, much faster than after a highway, higher RPM blast.

I just use the pyro as my gauge when to shut down. I never stop driving and turn off immediately in any situation though. Never did that even with turbo cars I've had.

 

[67Cougar]

I agree that the type of driving that you have been doing before shut down will dictate the amount of time that you need to let it idle before you shut it down. The harder you have been running it, the longer it has to idle to sufficiently cool the turbo down.

When I used to come home in my old Peterbilt I either had a nice gradual down hill if I came from one direction, and a little climb followed by a slight incline for the other. My EGT temps would always fall way faster on the slight down hill. I could drive with almost no boost and had a short cool down period. After the slight climb it would always take 7 or 8 minutes to cool down to the point where I felt safe so shut it off.

 

[m16ty]

I agree with most every thing mentioned, but I was always told that also, the idle time at shut down was to let the turbo run down from it's high RPM's and to have a supply of oil to the bearings during rundown. We have a older D8 K at work and even after a 5-10 minute idle, you can still hear the turbo slowing down after you shut it off.( If you had your ear plugs in, WHAT, HUH, YOU SAY SUMPTIN?)

The turbo will slow down within 30 seconds after going to idle. What you hear on the D8 is the turbo still slowing down at idle speed. The turbo will still continue to spin pretty fast even at engine idle. The only problem you'll have with turbo spinning too fast at shutdown is if you're running the engine at high RPMs and immediately kill the engine.