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6.6 serious drop in mileage while towing

TNCannons

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TNCannons New Member

TNCannons

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I have a 2014 GMC 3500 with 6.6 with 110k miles on it. Highway mileage is 20-22mpg when empty. I used to get 18-ish towing my 32 foot 5th wheel (14klbs) but now getting 9-12mpg. I had radiator and turbo replaced last year. Oil, fuel and air filters changed ahead of schedule....any thoughts? Transmission issue?

BigBadSierra Senior Enthusiast

BigBadSierra

Posted
Posted

Check the Turbo plumbing for an air leak. 

 

Do you feel like it has lost power and is revving higher to do the same job.

 

I assume there are no abnormal weather conditions involved it's amazing how bad your millage can drop just from added wind drag.

 

 

TNCannons New Member

TNCannons

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GMC replaced turbo but mileage stayed same. No leaks noticed. Idle does seem to be a bit high when in park but no other issues. Power is great, truck runs extremely well. I live in east TN at about 900 foot elevation so usually warm, no extremes in weather, just lots of rain. Where would I see turbo leaks? Appreciate your help and thoughts!

BigBadSierra Senior Enthusiast

BigBadSierra

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Posted

The leak may only occur under heavy load that's all I'm saying.. When the system is under higher pressure. 

 

It's worth a check.

2017Darkness Enthusiast

2017Darkness

Posted
Posted

EGR is probably getting sooted up. Some diesel fuel injection services may clean it up, or it may need replacement if it is too bad.

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