Turbo Cool-down

[HK416]

I just sold my L3130 and am awaiting delivery of my new MX 1500 in a couple days. Since I haven't received my owner manual yet, would you turbo owners chime in and tell me how much cool-down/idle time I need to do after running the tractor at normal operating speed? How about after I've run the tractor hard (bush-hogging)? Thanks!

-Podunkadunk

 

[TripleR]

http://www.tractorbynet.com/forums/kubota-owning-operating/183710-turbo-time-cool-down.html

 

[displacedPA]

I do this with my B2320. After Im working at full load i take it on a easy drive to let the rad. circulate air and cool the coolant down even more. Is it a must? Im sure not but, it does bring the temp down on the coolant gauge.

 

[nikdfish]

The cool down is to get to a temperature that is low enough not to carbonize or "coke" the oil around the turbo's bearing. The oil stops flowing when the engine is cut off, so it is going to get as hot as the turbo itself while it sits there.

As I recall, 5 minutes at low idle should do the trick, if you are not just finished with heavy use. If it's just been run real hard, give it a bit more time to be on the safe side.

Nick

 

[Ken45101]

If all of that extra running is really required, all I have to say is d*** stupid EPA. How much extra fuel and pollution is caused by that idle running?

The M9540 only gains one additional horsepower with the turbo. EPA forces the turbo requirement.

For me, I take the equipment back to the barn at a slow RPM and maybe give it 30 seconds before turning it off.

I'll have to check my pickup owner's manual but I don't remember any requirement to let it idle for 5 or 10 minutes every time I drive the truck anywhere! I can't imagine having to sit at idle for five or ten minutes every time I use it.

Ken

 

[kuboman]

It all depends on heat and speed. If you have been working the engine and the exhaust temps are up then your turbo will be spooled up too. The idea is to cool the turbo down and let it spool down. Heat cooks the oil when it is shut off hot and the speed will use up the oil supply as it spools down. If it has too much speed the bearings will run dry and with the heat coke the oil.
Idling around requires little cool down. 1 min is ample. Hard work requires 5 min or more. And not just for the turbo, as the engine temps should be allowed to stabilize also.:thumbsup:

 

[BeezFun]

The cool down is to get to a temperature that is low enough not to carbonize or "coke" the oil around the turbo's bearing. The oil stops flowing when the engine is cut off, so it is going to get as hot as the turbo itself while it sits there.

Are the temps in a turbo higher than the temps in the cylinder? Why doesn't the oil carbonize in the oil scraper rings, on the cylinder walls, and in the passageways between cylinders up to the head?

 

[BeezFun]

1) The combustion chamber is the hottest place around, but I'm VERY sure you already knew that.

I'm still not sure I know it. Turbos spin at 100K+ rpm, and they're driven off exhaust gases, doesn't seem impossible that local temps could rival combustion temps. I've never owned a turbo before, it seems strange that such a sophisticated piece of equipment is dependent on people sitting in their cars and tractors with the engine idling to cool it off. Do people carry magazines in their glove box to read while they cool down their saabs?

 

[scrappy isb67]

If all of that extra running is really required, all I have to say is d*** stupid EPA. How much extra fuel and pollution is caused by that idle running?

The M9540 only gains one additional horsepower with the turbo. EPA forces the turbo requirement.

For me, I take the equipment back to the barn at a slow RPM and maybe give it 30 seconds before turning it off.

I'll have to check my pickup owner's manual but I don't remember any requirement to let it idle for 5 or 10 minutes every time I drive the truck anywhere! I can't imagine having to sit at idle for five or ten minutes every time I use it. Ken

if it is turbocharged then it IS in the owner's manual!

Are the temps in a turbo higher than the temps in the cylinder? Why doesn't the oil carbonize in the oil scraper rings, on the cylinder walls, and in the passageways between cylinders up to the head?

but the block is water cooled and does transfer heat away from everywhere else but the turbo. that is unless the turbo is water cooled too.

1) I thought maybe you were pulling my leg on this and trying to set me up.

2) Combustion comes first. Things only cool down after that, but the turbo temp is definitely up there.

3) No they send text message or use their cell phones. The cool down isn't that big of an issue. Often you finish your work, cut the RPMs and loaf back to your parking area. That can provide most of your cool down time. In the case of the Saabs, they probably aren't really being worked before being shut off. Some manufacturers have even provided an oil reservoir that supplies oil to the turbo after the engine is shut off.

not necessarily, some are actually HIGHER in the manifold! one example is a Dodge Cummins during an active regen since fuel is still burning in the exhaust to raise the temps to initiate the regen.
most if not all newer automotive Turbocharged cars are also using water cooled turbos. which makes the cool down time not as critical. it is still recommended though.

 

[kuboman]

I'm still not sure I know it. Turbos spin at 100K+ rpm, and they're driven off exhaust gases, doesn't seem impossible that local temps could rival combustion temps. I've never owned a turbo before, it seems strange that such a sophisticated piece of equipment is dependent on people sitting in their cars and tractors with the engine idling to cool it off. Do people carry magazines in their glove box to read while they cool down their saabs?

As has been said most of the time the cool down happens as you park, unhitch, etc. The time a meaningful cool down is required is immediately after a hard workout. And even a non-turboed engine should be cooled down as many internal engine parts should have the temps stabilized before shut down. That time is dictated mostly by engine size (weight). A 2000# engine requires more stabilization time than a 200# engine.:thumbsup:

 

[MHarryE]

It's a good idea to let any engine cool after hard work. Older turbos had problems but new turbo technology and lube technology have lessened the need. My turbo equipped tractor says 3 minutes but I have always spent those 3 minutes, plus usually more, getting back to the yard after doing any tough work. My father-in-law is very impatient and always shuts the engine off no matter what he has been doing. His John Deere / Yanmar couldn't take the abuse (non-turbo) and cracked a couple valve seats. Give it a little time to cool things down evenly before shutting down and it will pay off in the long run, turbo or non-turbo.

 

[OrangeToys]

I think (not positive) that my book for the mx5100 says to let it slow down in winter months after its been ran a while. I guess ill have to go back and reread it. I don't recall anything else about the warm months.

 

[rsewill]

The first truck I owned was a '66 Freightliner that had a NTC 335 HP Cummins. It had no after-cooler but did have a pyrometer. The pyrometer was there so you could keep your turbo temp at 1100 F. or less. You watched the pyrometer far more than any other gauge. I think if I stuck my foot in it for a few seconds I could get it up to 1300. The relevant thing to this thread is that the temp would drop a second or so after I backed out of it, if I recall (or guess) correctly, to 600 or 700 degrees. I remember the high temp but really don't remember the low temp because it wasn't important. I would let the engine cool down two or three minutes but not because of the turbo but more so that all the other iron would cool a bit. When it was cold, say -30 or so, I could pour more fuel to it and the pyrometer wouldn't get over 1100 but I never trusted the reading to be accurate at that ambient temp so I would actually keep the pyrometer at about 900.

My last truck had an N14 Cummins turned up to 475 HP. The pyrometer never got over 900 degrees.

 

[scrappy isb67]

The first truck I owned was a '66 Freightliner that had a NTC 335 HP Cummins. It had no after-cooler but did have a pyrometer. The pyrometer was there so you could keep your turbo temp at 1100 F. or less. You watched the pyrometer far more than any other gauge. I think if I stuck my foot in it for a few seconds I could get it up to 1300. The relevant thing to this thread is that the temp would drop a second or so after I backed out of it, if I recall (or guess) correctly, to 600 or 700 degrees. I remember the high temp but really don't remember the low temp because it wasn't important. I would let the engine cool down two or three minutes but not because of the turbo but more so that all the other iron would cool a bit. When it was cold, say -30 or so, I could pour more fuel to it and the pyrometer wouldn't get over 1100 but I never trusted the reading to be accurate at that ambient temp so I would actually keep the pyrometer at about 900.

My last truck had an N14 Cummins turned up to 475 HP. The pyrometer never got over 900 degrees.

I have buried a 1600 degree pyro before! it was usually only for a few seconds and I let it run at idle 20+ minutes afterward. the rule of thumb I lived by was 300 deg. I actually had a turbo temp monitor set @ 300 degrees on that truck so I could turn the key off, lock the doors, and walk away and it wouldn't shut off until it was less than 300 degrees. if it was more than that at shutdown the exhaust temp would go UP after shutdown I.E. 400 deg. @ shutdown would be 550-600 a few minutes after shutdown. the turbo needs AIRFLOW to cool off!

 

[Jim Shooz]

Most auto-accessory shops should have a range of after-market turbo-timers which will allow the engine to idle for up to 5 minutes after turning off the key. I'm sure there would be one for a diesel or one could be adapted.

One was fitted to my 96 Subaru wagon when I bought it but I don't know if it did anything (except waste fuel). Felt kinda weird walking away from the car in the parking lot, with the engine still running.

Current vehicle is a 02 Subaru wagon with twin turbos. It has no timer but by the time I arrive home, check for mail, and drive the 300 yards to the house, it will have cooled down sufficiently.

I was told that a rough guide as to whether you need a timer or not is, at night, give it a good workout, turn off the engine and ALL lighting, and if the turbo glows red, you need a timer.

 

[scrappy isb67]

Most auto-accessory shops should have a range of after-market turbo-timers which will allow the engine to idle for up to 5 minutes after turning off the key. I'm sure there would be one for a diesel or one could be adapted.

One was fitted to my 96 Subaru wagon when I bought it but I don't know if it did anything (except waste fuel). Felt kinda weird walking away from the car in the parking lot, with the engine still running.

Current vehicle is a 02 Subaru wagon with twin turbos. It has no timer but by the time I arrive home, check for mail, and drive the 300 yards to the house, it will have cooled down sufficiently.

I was told that a rough guide as to whether you need a timer or not is, at night, give it a good workout, turn off the engine and ALL lighting, and if the turbo glows red, you need a timer.

if the turbo is glowing red you are well north of 1000 degrees!

 

[Dan Hunter]

Unlike a gas engine that controls both fuel and air cycling through the engine, at idle with no air restriction (but granted no turbo boost) very little of the oxygen coming in the engine is consumed by combustion. Turbo or not I'd think you'd want to bring the temp down.

 

[BeezFun]

I'll still stick with my answer.

I found a carnot map of the diesel cycle and it says typical combustion temp is about 2025C. I found this video by Honeywell about it's high temp turbo ball bearings that says temps can go as high as 1000C and they designed the Mercedes passenger car turbo for 860C. So unless tractors are significantly different than autos, combustion temps seem to be about twice turbo temps.

 

[Kabuki Tractor]

I found a carnot map of the diesel cycle and it says typical combustion temp is about 2025C.

Exactly, the air temp in the combustion chamber may reach 2025C (3677 degrees Fahrenheit) for a short period of time, but no part of the engine is reaching that temperature. Specially the aluminum piston which will start to melt under 1,400F. Shortly after each short burst of heat is plenty of time for the heat to dissipate away from the combustion chamber with the help of water and a nice fresh gulp of cold (120F) air. The exhaust valve is probably the hottest part inside the engine.

It is not at all uncommon to see the exhaust manifolds and turbos glowing cherry red on a heavily loaded engine (gas or diesel), but you won't see the block or head glowing red on the engine. So my guess is with the exception of the exhaust valve, the turbo can get hotter than any other part of the engine.

Like said before, turbos will cool rather quickly once the load is off the engine, specially on a diesel. Unlike a gas engine with a throttle plate restricting the airflow through the engine, a diesel at idle is flowing a massive amount of cool air through the engine. What you don't want to do is be plowing a field at full load then stall the stall the engine with your turbo glowing cherry red! When that happens you need to get it started quickly and get the oil and air moving through the turbo again before your oil turns to carbon.

 

[megaboz]

Well at least in my opinion based on owning a diesel pickup, I would say 2 to 3 minutes tops to get it down to a safe temp unless it was extremely hot.

There is no doubt that just shutting them down isn't good but if it were that bad I don't think too many people would buy a time bomb.