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Old 06-16-2015, 12:21 PM   #1 (permalink)
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Oil Burning 2013 GMC

Very frustrated with my 2013 GMC Truck. From day one its been burning oil. Now it uses around 1 quart every 1000 miles!!!! I have been researching this issue and so far it looks like the AFM Active Fuel Management is the problem.

For years, GM has touted the AFM system as their way to save consumers fuel. The system basically shuts down cylinders when not in use meaning that a V-8 is a V-4. It isn’t a new technology and has been around since the end of WWII. Yet, for the last several years that GM has used it, owners have complained about excessive oil use.
What causes the Oil Loss?

The owners that have reached out to us and the complaints we have read about say that the AFM is directly responsible for the problem. Many of them have bought after-market tuners to deactivate the system which they claim stops the loss. The reason seems to be that when the engine deactivates a cylinder, the oil doesn’t simply sit in the head, it either gets pushed out of the shaft or soaks into the rings. This then causes a loss of oil.

Officially GM says:

This condition may be caused by two conditions. Oil pulled through the PCV system or oil spray that is discharged from the AFM pressure relief valve within the crankcase. Under most driving is discharged from the AFM pressure relief valve within the crankcase. Under most driving conditions and drive cycles, the discharged oil does not cause a problem. Under certain drive cycles (extended high engine speed operation), in combination with parts at the high end of their tolerance specification, the oil spray quantity may be more than usual, resulting in excessive deposit formation in the piston ring grooves, causing increased oil consumption and cracked or fouled spark plugs (#1 and/or #7).

GM has issued a fix for this which is a shield that keeps the oil from disappearing. What’s a bit surprising is that GM’s latest TSB addressing this issue was released on January 3, 2013. It addresses the problem in 2007-11 trucks with the new shield.

Source Chevy/GMC AFM Cylinder Deactivation Excessive Oil Consumption | Tundra Headquarters Blog

This week I'm going to try to see if by running it in manual shift mode and keeping it out of 6 gear, I will see any difference in oil consumption and fuel mileage? By doing this I noticed it doesn't drop into 4 cylinder mode.

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