Turbo Cool-down

[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.