Chevy/GMC AFM Cylinder Deactivation Excessive Oil Consumption – Ongoing
The Active Fuel Management system that GMC/Chevy has used for years, is well known to excessively use oil. GM has updated a fix and it doesn’t seem to work 100 percent of the time. Will the problem ever go away? Is Cylinder Deactivation just a bad technology?
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.
Also interesting on the TSB is that “engine oil consumption of vehicles with higher mileage (approximately 48,000 to 64,000 km (30,000 to 40,000 mi).” And that GM has changed their accepted oil consumption level from 1 quart per 2000 to 1 quart per 2000 to 3000. Plus, GM used to have customers come back multiple times to confirm the problem, this has since been removed.
It is rather bizarre that GM considers 30-40k miles “high.” Yet, it would explain why the current “fix” only goes through 2011 products. It will be interesting to see if it gets expanded down the road.
Does the Fix Work?
The shield fix for many owners seems to help somewhat. We hear they go from losing 1+ quarts to less than that. Yet, we hear that dealers are still going through the process of replacing parts as part of their diagnosis. They will replace the the valve covers, oil deflector, new lifters, pistons and rings. Then, the shield. If none of this fixes the problem, then the dealer swaps in a new engine as a last resort.
We have heard that their are some owners who are on their second engine.
Why Cylinder Deactivation?
For GM, the AFM is their way to meet the 2016 CAFE regulations for fuel consumption. Their new pickups claim much better fuel economy by using this system. The range we hear is about 2 mpg on highway and 1 mpg on city. If they didn’t have it? They would not be able to meet the CAFE regulations and GM might have to pay fines.
And yet, if consumers are constantly monitoring/adding oil – aren’t the customers losing the fuel savings?
What about other makers?
It is worth noting, Honda owners are having similar issues with their Variable Cylinder Management (otherwise known as cylinder deactivation). Here is a great article detailing the issue.
Chrysler uses it as well, yet we haven’t heard of many complaints.
As of this time, there are no Toyota products in the U.S. that we know of with cylinder deactivation.
Are you still a fan of cylinder deactivation systems? Is it a bad technology or a simple fix?
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