Chevy/GMC AFM Cylinder Deactivation Excessive Oil Consumption – Ongoing
Tim Esterdahl | Sep 16, 2013 | Comments 25
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?
The AFM systems in Chevy/GMC products have oil consumption issues. Is it permanently fixed or an ongoing issue with that system?
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.
This is the shield that GM is putting on their engines to stop the AFM from causing excessive oil loss.
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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Filed Under: Auto News
For two auto manufacturers to have the same problem suggests that the technology is defective.
Also, this is a win for “if it ain’t broken, don’t fix it” camp.
For the new GM engines that make use of AFM, there is more decactivation with them than in the previous generation-I wonder how this will pan out.
LJC,
I tried to find information on the new EcoTech engines GM has developed, but they are just too new. My guess is tt will be next year or thereafter when we get to hear something (needs to age/mileage). I’m keeping on the look out.
-Tim
LJC,
Yep. I found it quite interesting that Honda is having the same problem. For both of them to have the same concerns leads me to believe the technology is to blame.
-Tim
My hunch is this: the lack of pressure from the combustion cycle on the top side of the piston is allowing oil to sneak by from the bottom side of the piston.
Now, couple that with the use of thinner oil and there is a greater opportunity for more oil to sneak by the rings.
LJC,
That sounds good to me. 🙂 I’m far from a mechanic.
-Tim
Low pressure and thin oil. That sounds like a possibility.
Usually the top piston rings are different. In the past some had a bit of a wedge shape to get compression to expand them out a bit. The lower rings were oil control rings which were more flexible to keep the ring in contact with the cylinder wall and to scrape oil down into the pan. Some even had springs behind the ring to force the outward.
I would assume that most of these systems just open a valve in a lifter which allows the oil to pump out instead of pushing the valve open. This would make the piston an 8:1 air spring with no fuel injected. I doubt the injector would add any fuel at all. In active cylinders there is always some excess fuel which does not burn and is there to lubricate the upper cylinder wall and keep combustion down. EGR allow us to cut back fuel even more but, they have always had the problem of getting gummed up.
Open valves would not be a practical solution unless there was a a way to keep the valve open which would be more complex then a valve in a hydraulic lifter.
It would seem we are really reaching the upper limit on the efficiency of a V8 motor. AFter variable valve timing, valve deactivation and double cam profiles what could be left?
EGR was always the way of cutting back fuel in the past. Recycle CO2 and CO back to the intake and then we cut back the fuel.
If they can make this stuff work I would be all for it but any failure will cost much more the n the fuel saved.
I would still vote for the plain Tundra V8 for now but there is no way this stuff will not become the standard. Big engines use fuel and the Feds are trying to change that. For those who can’t live with the 275-300 HP of a a non-turbo V6, the additional power will come with a cost.
My thoughts exactly.
Wow! People complain about the engine we have. Now the question is do you want that GM engine or what you now have in your Tundra? Cylinder deactivation sounds good, but now you know the rest of the story.
While I don’t like complex systems like this due to long term costs, I am not buying into the notion that piston rings are involved. The rings scrape oil down the cylinder walls on the under side of the piston. Most of the oil is in the bottom of the engine not the top. There should be virtually no oil above the piston unless an engine has bad valve guides which would not likely be related to deactivation. Could GM be building new engines with bad valve guides, sure, they can’t seem to get anything right.
Who ever is writing this stuff seems to be grasping for something and at this point they just don’t know.
This is just the tip of this iceberg. With the Feds moving trucks to the 30 MPG requirement, all kinds of complex stuff is going to start showing up in these engines.
I have just found an 8 year old cummins 5.9 Ram with 50,000 miles. I might buy it just because it’s a simple engine exhaust system which should last long enough that I don’t need to buy into all the new unproven stuff being forced upon us.
Get ready folks because this stuff is coming to a Toyota dealer near you soon. Toyota will not be able to keep these power numbers and meet the light truck Fuel numbers. They will have no choice but to move to a smaller displacement engine and boot power with turbo pressure or create a smaller displacement by shutting off 4 cylinders.
There is no free lunch on this one.
I would assume Toyota can build a cylinder shutdown system which does not consume oil. GM can’t build anything. Remember the gas motors converted to diesels back in the 70s?
Larry,
I tend to agree with you about the rings, EXCEPT, every owner story I heard and read said that the dealer replaced the rings. Must be something to that.
For myself, I am guessing this is part of the reason why Toyota hasn’t offered cylinder deactivation. They have to know about the oil consumption issue and probably haven’t sufficiently tested it without losing oil. My two cents.
-Tim
I’m no expert in GMs system, but don’t the valves need to crack open during deactivated cylinder compression stroke so the active cylinders power stroke does not need to overcome the compression? Lack of compression reduces ring to wall pressure so less seal and the oil that gets by has open valves to get out.
I hope Toyota doesn’t do it – complex and costly system that is more prone to failure for minimal payback that does not make up for it (my 2 cents). There are better ways of improving mpg that are better long term investments – like evolve 1/2 tons to lightweight aero flat/dimple-bottomed beer cans with electric accesoories (AC,fans,stearing,etc…) and rely on traditional tech for lower volume HD or 3/4 ton models.
I don’t think the valves on the deactivated cylinders open at all.
I know they did not open on the old GM systems which had so many problems.
They worked by cutting off oil flow to the valve lifter. With no oil the lifter body would just compress and not lift the pushrod/valve. With oil they would only compress a bit until a valve in the bottom closed then the lift would start. This pumped oil up through the push rods to lubricate the rocker arms. Way back when hydraulic lifters replaced solid ones making for better oil flow to the rocker assemblies.
The new engines are over head cam but could still have a lifter device. So it’s likely they work the same way. I don’t see a way to partially open a valve once oil flow to the lifter has been cut off by an electric valve.
This puts the cylinder/piston into air spring mode which does waste some energy. Even if the valve was open we still have the start and stop loss of the piston motion due to their mass along with the mass of the ratting crank for the 4 cylinders which have been shut down. These big engines don’t produce 400 HP for free.
I know how valves and cams work and there are only a limited number of ways to prevent the cam lobe from pushing up the rocker arm. I have been looking for a while for technical papers on the mechanics of how each manufacturer implements this stuff but, the just don’t publish it on their web sites. I guess people are not supposed to think about or evaluate it, don’t ask questions, just eat it.
GM has also talked about split cam profiles. This is in addition to variable cam timing. 4 cylinders get different cam lobe grinds which changes the lift and duration of each valve. This creates 4 cylinders for lows power cruise and the other 4 for higher compression and higher power.
Well I could have purchased any truck out there. I have been burned so bad with “new technology” that could not deliver the goods, and neither the manufacturer nor the dealer(s) would stand behind them. Nor could they fix them. Nor did they provide an easy way out of the truck.
Knowing full well the nightmare of all Cadillac’s with cylinder deactivation pushed me to steer clear of both GM and RAM (hemi).
I will “never” buy another truck with an intercooler unless the “manufacturer” can prove it actually works. And so far “no company” can prove that to me, because they can’t.
That is one reason I am now in a 2014 Tundra. I only want the most reliable and dependable truck made that is safe to drive.
I forgot about the Cadillac valve deactivation mess.
So,,,,,,, I guess you won’t be moving to the twin turbo Ford V6?
That makes 2 of us.
I got burned by GM back in the 70 when my trucks started rusting out after about 18 months. They told me to get stuffed and I then said the same to them. Since then I have purchased about 10 cars and trucks. If I live long enough I might by 5 more.
That’s a total of 15 cars and trucks not built by GM.
Talk about stupid management and a stupid congress who keeps them in business. So much for buy American.
Your second line: “So,,,,,”
Unfortunately, I was already burned badly. I am now having T-Shirts printed: “Just Say NO EcoBoost” with a big circle an slash mark on it.
Does the RAM have the same problem?
LJC,
Good question! I forgot that Ram had the cylinder deactivation myself. Doing a quick internet search, I’m not seeing a lot of activity around this topic on the Dodge Forums I am on. Interesting. I would say that with all the changes with Ram, owners probably aren’t connecting the dots yet of oil consumption and cylinder deactivation. With GM having less changes, over the last several years, it is probably easier to pin point the issue. Other than that, I’m not really sure what’s going on.
-Tim
Now that the problem is out there in the open, will Toyota, it it decides to go with this technology, make a system that does not consume oil? Will they rush something to market leaving us to deal with its problems later? By the way, ALL my small block Chevy based trucks consumed huge quantities of oil. That was without deactivation.
Should we have a choice to deactivate the system in the event we conclude that cylinder deactivation should need to be revisited in some other time? The Audi A6 for example allows the driver to deactivate its system. I would pursue that option and even buy that car if I am forced to deal with this flawed technology.
Most modern engines seem to drink more oil than their older siblings. However, my ’02 Duramax consumed little if any oil between 3k oil changes. This is but another point in favor of diesel.
It seems car companies are not wanting to address issues head first such as bloated curb weights and antiquated engine technology. But on the political front, the US gov is keeping needed diesel technology at bay, technology that would help offset weight and high fuel prices, by increasing its onerous CAFE regulations too quickly and raising its MPG ceiling too high. The profit motive aside, this creates an unreasonable environment for a profit based company to even stay afloat. GM and others are trying to cope with a system that is against them and ultimately us.
CAFE is the real problem here. Now couple that with a gov already obsessed with “climate change” and bent on ending our domestic oil output, and we have Europe.
AAA said today $3/gal gas in the US is here to stay.
Rick,
There is a “tune” to deactivate the GM system. It is quite popular from what I understand.
-Tim
I’m not a fan of cylinder deactivation don’t think the at most 1 more mpg makes it worth the potential headaches. Ford’s twin turbo v6 is fine for racing off the line, but my HD/Ford fanatic co-worker even states his new ford f150 turbo v6 is quick off the line but not too impressed especially with gas mileage pulling a cattle trailer.
Face it, for a mere 1-3 less mpg at most, the tundra 5.7L is in my humble opinion still the best, most reliable, most pulling power for the money, 1/2 ton truck engine/tranny on the market still today. Just wish somehow they could tweek 2 more hwy. mpg out of it is all.
Well if you ask Consumer Reports EPA numbers are bull. The Tundra not only earned the best MPG numbers in their thorough real-world testing, but it had the quickest acceleration. These were all 2013 trucks being compared.
Even with this excessive oil comsuption issue, I would still commend GM’s effort to try to increase the gas milage of its trucks. Fuel efficiency was one of the major reasons why Americans were switching to Japanese cars in the past. I think the Tundra engineers should not lose sight of this important fact.
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Old thread I know, but I’m glad to see the article. This is exactly the reason I made the switch to Toyota. I’ve owned 3 GM trucks up to this point, the last being a 2004, and driven new GM vehicles constantly as a Gov’t employee. After reading the horror stories on GM forums about entire top end replacements, warranties not covering 2nd return trips and no real solution to their problem, I couldn’t buy a truck that would need an engine overhaul at 30-40K miles.
Another interesting point, the service bulletin which I’ve read many times states the problem only occurs at constant high engine speeds…. However, AFM only deactivates cylinders at LOW engine speeds. Put your foot in it, and you have all 8 again immediately. To me, that just didn’t make sense. I hope Toyota sticks to their guns and keeps turning out solid, strong full-size pickups.
Good point on the lower speeds. And thanks for commenting!
-Tim