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Old 05-24-2010, 05:48 PM   #1
David and Jo-Anna
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turbo getting coked--cause? solution?

Pam Martin recently reported that the reason the turbo hose on their 2005 F350 was blowing was because the turbo was coked and that their Ford dealer told them they should henceforth add cetane with every fillup to prevent future coking.

I took my 2007 F350 in today for routine service and asked the Ford service manager about the coking issue. He said that coking is caused by idling the engine too long and that, while cetane can help with fuel mileage and engine lubrication, it won't prevent coking.

Clearly we have a difference of opinion amoung Ford service managers. Anyone know the actual facts about the cause of coking in the turbo and what to do to prevent it?
 
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Old 05-24-2010, 07:43 PM   #2
Sinterior
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I'm no expert but have heard that shutting the engine off right after a long hard pull without letting it idle to cool down for a few minutes will "cook" the oil in the turbo bearings.
Could this be the same thing?
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Old 05-24-2010, 10:39 PM   #3
KTManiac
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Quote:
quote:Originally posted by Sinterior

I'm no expert but have heard that shutting the engine off right after a long hard pull without letting it idle to cool down for a few minutes will "cook" the oil in the turbo bearings.
Could this be the same thing?
Yes, that will coke up the oil lines and kill the turbocharger bearings, keeping it from spooling up and producing positive pressure.

But what they are talking about is the new generation turbochargers that have variable adjusting vanes. What happens with these is that the vane mechanisms can get all carboned up (coked) and get stuck so that they cannot adjust to the different demands placed upon it. If they get stuck in a low pressure position, you don't make enough boost to get the power that you need. If the get stuck in a high pressure position, it produces too much boost in heavy load, high RPM situations, and BOOM!, there goes the boost hose, or worse, the inter-cooler.

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Old 05-25-2010, 01:22 AM   #4
SlickWillie
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Another reason for a good synthetic oil.
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Old 05-25-2010, 03:52 AM   #5
skypilot
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Will: The synthetic oil won't help in the situation KT described since it is all the carbon coating the sliding mechanism which is causing the problem here -- synthetic will sure help the first one though - shutting down while the turbo is still too hot causes the dino oil to cook off leaving the bearings unprotected. The synthetic, having a higher boil point, shouldn't cook off as badly thereby giving the bearings some lubrication. Still not a good idea to shut down hot -- but with these new engines you can never get the EGTs down low enough it seems without excessive idling -- then you get the problem KT describes -- all kinds of carbon coating the turbo vanes since the engine isn't running hot enough to burn it off. Catch 22 it seems.

Regardless, in the case of the Dodge engine, all of the diesel techs I've spoken with have recommended running with the 'Exhaust brake' on at all times (this forces the variable vane turbo to cycle) to keep it cleaner. Too bad Chrysler didn't / doesn't make that the default instead of having the driver turn it on every time you start up. However, that is another issue and I don't mean to hijack this thread.
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Old 05-25-2010, 03:57 AM   #6
8e3k0
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Please remember that all diesel fuels are not the same and even though refineries have specs to meet; quality can and will vary from plant to plant and company to company. It may be called coke but it is likely tars that drop out after combustion because of temperature variations ( from a liquid to a solid ). I have not heard of any problems in the Northwest as noted from the many discustions. Maybe that is because our crude comes from the Tarsands and manufactures into a high quality diesel product. Great many trucks up here are run hard from plus 90 to -50 F from summer to winter and run 24 hours a day much of it idling, with no sooting or slobering. Easy on engines to leave them running when cold than to stop start multi times each 24 hour period. Maybe we baby those engines too much and cause all these problems. Company trucks are always loaded, and driven hard over very tough conditions some 60,000 to 100,000 miles per year. a lot of these trucks just see minor maint. like oil changes. Just some thought and experiences of the Oil Patch life.
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Old 05-25-2010, 12:30 PM   #7
danandbetty
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I agree with 8e3k0 - in Alaska many of our diesels run around the clock without these kinds of problems. Perhaps there's a fuel difference or it's the amount of time they're driven hard pulling loads and keeping all the soot burned out in between idle times.

That said, with my 6.7L Cummins, I hwy commute about 50 miles per day plus one round trip of 300 miles over Turnagain pass and back once each week. From the hwy, as I approach the area where I want to stop I try to get off the 'pull' for as long as possible to help reduce engine temp and internal pressure while still rolling - I don't stay on an extended idle after stopping but I do let it 'come down' for several minutes when I pull in off the hwy (like at a rest area) before shutting down.

I don't know from beans what's really going on inside the ol Cummins but so far i haven't had any problems from this strategy. All said and done - I don't know anything but I'm willing to comment anyway...cheers
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Old 05-25-2010, 04:57 PM   #8
sreigle
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Skypilot, I don't run the exhaust brake all the time but do often reach over and turn it on when ready to exit a freeway and not towing. Or sometimes when on mountain roads and not towing I'll use it as a method of downhill speed control. My selling dealer told me to turn it on occasionally to keep the carbon from building up. They said just cycling it on and off is enough but I'll leave it on a few minutes now and then.

David and Jo-Anna, I don't have an answer for you but I can't see where a cetane boost will stop coking. I've heard as other said that it comes from 1) shutting down with engine very hot, 2) idling too long at low idle rpm, and 3) regular carbon buildup from babying the engine too much. I don't know for fact if any of those are correct. Synthetic should help the first, as noted above. Also, I've been told I don't need to let it idle to cool down in most circumstances but when stopping after towing up a long grade I should give it a little time to cool down. Otherwise, by the time I navigate the rest area entrance and get parked is supposedly long enough. Except after that long grade. The Dodge has a feature for fast idle that my dealer "turned on." I just turn on the cruise and hit Set. Sometimes I have to hit Set a second time if the first time didn't increase the idles. My Fords, 2003 and 2005, both 6.0L would both automatically increase idle rpm after a couple of minutes of idling.
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Old 05-25-2010, 05:04 PM   #9
rotti
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Check out the you tube videos about the 6.0 and 7.3 ford diesel motors they are very interesting..
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Old 05-25-2010, 06:39 PM   #10
David and Jo-Anna
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Rotti--thanks for the link to the videos--I found them worthwhile.

With regard to the coking issue I raised in this thread, the message I got from the videos is that there are at least two basic issues to consider to avoid coking/carbon buildup in the turbo: (1) avoid "dirty" diesel fuel, especially the old low-sulfur diesel; and (2) put your engine under heavy load from time to time to get hotter exhaust gases that can help burn out carbon buildups in the turbo. Does this sound right to those of you who are knowledgeable about the 6.0 engine? Are their other things to worry about, like extended idling? And how much idling constitutes "extended" idling. While I don't just sit in parking lots with the engine idling, I do keep the engine running while I am leveling the rig and chocking the tires and getting ready to unhitch. Do I need to rush thru that process and/or shut the engine off while going thru the unhitching process?

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Old 05-26-2010, 12:40 AM   #11
steves
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Dave, Think your observations are right on. I don't think your unhitching time falls into the "extended" classification. I read a post on one of the diesel forums that said the 6.0 should be driven "like you stoled it" I guess they were referring to keeping the carbon blown out of the turbo.
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Old 05-26-2010, 02:55 PM   #12
bob n pam
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Drive it like we stole it? Man, that takes me back to how I drove as a teenager! Yahoo!
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Old 05-26-2010, 04:38 PM   #13
cbgaloot
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Lots of good videos on powerstrokes here.

http://www.powerstrokehelp.com/

I highly recommend that anyone with a powerstroke watch them all.
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Old 05-26-2010, 06:08 PM   #14
sreigle
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Quote:
quote:Originally posted by David and Jo-Anna

Rotti--thanks for the link to the videos--I found them worthwhile.

With regard to the coking issue I raised in this thread, the message I got from the videos is that there are at least two basic issues to consider to avoid coking/carbon buildup in the turbo: (1) avoid "dirty" diesel fuel, especially the old low-sulfur diesel; and (2) put your engine under heavy load from time to time to get hotter exhaust gases that can help burn out carbon buildups in the turbo. Does this sound right to those of you who are knowledgeable about the 6.0 engine? Are their other things to worry about, like extended idling? And how much idling constitutes "extended" idling. While I don't just sit in parking lots with the engine idling, I do keep the engine running while I am leveling the rig and chocking the tires and getting ready to unhitch. Do I need to rush thru that process and/or shut the engine off while going thru the unhitching process?
Ours idles about the same as yours when unhitching and usually leave it idling a bit to warm up after hitching, while de-chocking, etc.
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Old 05-26-2010, 07:40 PM   #15
clutch
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Excessive idling will soot up the turbo. If you have high idle enabled you can idle a little longer. I only let my truck idle long enough to cool the turbo down to around 350* before I shut the engine off. Also useing the the exhaust brake on the 6.7 Dodges will help keep the DPF clean. If your newer DPF equiped truck ever plugs up and you are out of waranty you will not like what it will cost.
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