Turbo cool-down or spin-down?

[klenger]

Following are some-out takes from a thread on another forum. I'm interested in comments on this. I hope that taking these comments out of context does not change the meaning of them. Emphasis was added by me.



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All engines need to be warmed up. Most Diesels have a turbo which need up to 5 min to spool down. Same thing for a gas with a turbo. Of course you don't have to but then after you buy a turbo you will know why it is recommended.



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You must mean COOL down. With little exhaust gas drive at idle speed, a turbo will spool down rapidly. Cooling EGT's down to ~300 deg F before shutting down the engine to dissipate the heat stored in the exhaust components goes a long way toward extending the life of the turbo shaft bearings.



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Actually it is spool down. If you pull off the road and the turbo is spinning at 200K rpm, and you shut down the engine the oil flow drops to nothing. The bearings in the turbo no longer have the oil for cooling and lubercation. When the bearings go the turbine and compressor vanes contact the housing turning the turbo into scrap metal. There are electric oil pump systems and accumulators that can continue to provide a oil supply after shutdown. My daughter listened to me and lets her SRT4 turbo spool down before shuting her new car off.



I base the opinion off 36 years as a professional mechanic, 26 years of teaching mechanics, having worked on HD trucks, working on cars, replacing turbo's on Italian preformance cars back in the early 70's, and being an ASE Master Auto, Master HD Truck, Tech.



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I asked about the spool down time while I was at the Diamler/Chrysler training center this summer. The Instructor not only agreed with my opinion but said DC recommended 5min. My 05 CTD manual says 1 to 5 min.



Driving conditions play a part. If you pull off the interstate and into a fuel station the turbo is still wound up and needs a full 5 min.



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I don't think I buy the 5 min. spool down time. One of the complaints that many have about manual transmissions with a turbo diesel is that the turbo spools down during a gear shift. I don't think it takes 5 minutes to shift from one gear to another. Spool down is not the same as cool down. I also suspect the 200,000 RPM number. I don't know what the actual turbo speed is, but 200k seems a bit high (like by a factor of 5 times or so).



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While turbo's slow down and boost drops during a shift, the turbo does not slow to a level safe enough to shut down. Turbo's on gas engines have been measured to 300K to 500K rpm. You might want to review your owners manual. The manual on my 05 CTD says up to 5 min. It's your vehicle, do as you like. I have worked on turbo's for close to 30 years. My late FIL and BIL worked for Pro Diesel (formerly Diesel Sales & Service) Bil in the turbo shop. I'll stick with what I have learned from experience, advise from those who rebuild turbos, the Diesel instructors with Diamler/Chrysler and the published recommendations.

 

[Devan Manis]

I'd stay as far away from that guys shop or where ever he works as geographicaly possible. 30 years and he still hasn't learned what i learned in about 5min. hmm

 

[WDixon27]

maybe if the turbine weighed 25 pounds it'd take 5 minutes to spool down, at a few oz it just doesn't have the mass that and the air it's drawing in is creating drag slowing the turbine

 

[Bob Cochran]

For sure we are talking about cool down. If I am towing my 14,000lbs 5er up a 6% grade and just top out and pull over to a stop to take a leak and shut the engine down!! You bet I need to let the exhaust (turbo) cool down before shut down and 5 minutes would probably be minimum under those circumstances. If I am driving around town unloaded at 25 MPH probably would not bother although it may not hurt to wait a minute. Least that is my opinion!!!

 

[nickleinonen]

maybe if the turbine weighed 25 pounds it'd take 5 minutes to spool down

even then it won't take that long. the cool down period is important, more so than the "spool down" period. actually, how long the charger keeps spinning after shutdown is somewhat of an indication as to the conditions of the bearings within it

[at least on larger turbo engines i work on - 30sec min spooldown time from idle, idle turbo shaft speeds ±1500rpm, full load ±25,000rpm shaft speed]

 

[rbattelle]

I agree with everyone else (and Nick certainly should know about this stuff... he works on trains). There's no way a turbo takes 5 minutes to stop spinning. The guy is confused between spool down time and cool down time.



I knew something wasn't quite right when the guy spelled "lubrication" "lubercation". :-laf



I've learned that many people honestly believe that a false fact, long held, somehow becomes true fact.



-Ryan

 

[Lorenz]

I've learned that many people honestly believe that a false fact, long held, somehow becomes true fact.



-Ryan

That right there was first stated by one of the leaders under Hitler's Nazi Germany, he was refering to propaganda.



If you say a lie long enough, and loud enough it will become truth.



Totally off subject but I couldn't help it.

 

[rbattelle]

That right there was first stated by one of the leaders under Hitler's Nazi Germany, he was refering to propaganda.

Yikes! I thought I had come up with that myself... now I feel kinda dirty.



-Ryan

 

[EMD Diesel Power]

even then it won't take that long. the cool down period is important, more so than the "spool down" period. actually, how long the charger keeps spinning after shutdown is somewhat of an indication as to the conditions of the bearings within it

[at least on larger turbo engines i work on - 30sec min spooldown time from idle, idle turbo shaft speeds ±1500rpm, full load ±25,000rpm shaft speed]

And Nick is always on the ball... . (as well as beating my *** in responses :-laf ) by the way, the impeller weighs about 40 lbs or better... . so 25k rpm may not seem like alot... . but I have seen one of these things let go and wind up 100 yards into a cornfield. Oh yes, it took out the carbody doors neat as you please and bent the handrail 90 degrees . :--)



As Nick pointed out... it takes the turbo about 25-30 seconds to spool down. The 5-7 ton crank also takes about the same time... . roughly 20 seconds or so... . really weird when you've been listening to heavy metal and then dead silence and a soft whistling as the crank spins down.



The B-series turbos in the Rams run at speeds of up to 100k rpm.



As for cooldowns..... the Ram takes 5 mins after full load operation.

EMD locomotives have a Turbo Auxillary pump that runs after shutdown for 20 mins. regardless of previous load for oil supply to turbo bearings. Not sure what the GE setup is. probably something similar.



This pump is a riot when the turbo has blown up on the road... usually keeps pumping oil out all over everything and starts fires until somebody pulls the breaker or main battery switch. :-laf :-laf :-laf

 

[GaryCarter]

Heck, a 747 engine doesn't take 5 minutes to stop turning.



Gary

 

[nickleinonen]

The 5-7 ton crank also takes about the same time... . roughly 20 seconds or so... . really weird when you've been listening to heavy metal and then dead silence and a soft whistling as the crank spins down.

the emd cranks actually stop much quicker than that [±10sec] you can see the air comp driveshaft stopping when you grab the layshaft and pull it to no fuel. the ge evo and fdl engine take a good long time winding down from idle till they stop when you hit the stop button or grab the layshaft and go to no fuel [2-3x longer than an emd engine]

Not sure what the GE setup is. probably something similar.

the fdl series ge engines [dash7/8/9] have no prelube pump/turbo soakback pump system on them. but the turbochargers on them are water cooled [the emd one is only oil cooled] the new ge evo series 12 cylinder engines have an engine prelube system on them, that runs for 2-4min before engine startup [all computer controled from the moment start button in cab is pressed] but to the best of my knowledge [haven't worked on them yet as our order hasn't come in, but i did spend a week down at GE in erie on a training course on the engine 2 weeks ago] the prelube pump system is only used pre-startup and when maintenence is done. at shutdown, it doesn't run.

This pump is a riot when the turbo has blown up on the road... usually keeps pumping oil out all over everything and starts fires until somebody pulls the breaker or main battery switch.

great on the sd70's. . the battery switch can be out and the pump runs, as the turbo pump breaker bypass the knife switch. [and they have them little cap over the breakers making them hard to turn off ]

 

[JOdell]

Hey Nick, Can you explain the pictures in your Readers Rigs with the Ford and HUGE DUMP TRUCK. What happended and is everybody OK? -Jason

 

[WDixon27]

kinda brings to mind the part from caddyshack where rodney dangerfield tells ted knight "hey you scratched my anchor"

 

[EMD Diesel Power]

great on the sd70's. . the battery switch can be out and the pump runs, as the turbo pump breaker bypass the knife switch. [and they have them little cap over the breakers making them hard to turn off ]

And they say technology is grand.



I couldnt remember the exact time on the EMD crank spindown, but I also did the same thing, watched the AC driveshaft stop spinning. Had one guy try and go to reset an overspeed trip (intentional test) and I was yelling no..... she's still turning..... hes like BS... I cant hear it. and here I am pointing at the spinning AC shaft. :-laf :-laf :-laf



I forgot about GE turbos being watercooled. Thanks for the info Nick! Wish I was still in the business.

 

[biggy238]

Looks like the cat got away from somebody..... It has a cart under the rear tires... I hope somebody wasn't servicing that thing when that happened.

 

[NoSeeUm]

That makes no sense to me.



Watch the boost pressure, isn't that an indication of spool down or spool up? Boost pressure moves as fast as RPM on the tach.



As to cool down I agree. I am not sure of the temperature at which a non-synthetic oil will coke, but I let my EGT settle to a solid 350 minus prior to shutting down.



Jim

 

[WDixon27]

the power of the uninformed is sometimes amusing, once i was told my cummins should be making 5# of boost at idle

That makes no sense to me.



Watch the boost pressure, isn't that an indication of spool down or spool up? Boost pressure moves as fast as RPM on the tach.

 

[Sageair]

I've learned that many people honestly believe that a false fact, long held, somehow becomes true fact.



-Ryan[/QUOTE] You mean Ford doesn't own Cummings :-laf

 

[nickleinonen]

Hey Nick, Can you explain the pictures in your Readers Rigs with the Ford and HUGE DUMP TRUCK. What happended and is everybody OK? -Jason

i found those pics somewhere on the net, and i have heard many stories about the situation, but the one that seems to be most real is. .



the operator of the cat was on his/her lunch taking a snooze in the cab, service truck pulls up into blind spot. operator of cat wakes up, and drives off. crunch.

i don't believe anyone was hurt in the situation. .



some of them cabs can be very comfortable [heck, i have snoozed off a couple dozen times in the cabs of locomotives. they rock you to sleep when the engine is running]