Latest Reader Question (Nov. 4, 2017)

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Here is the latest reader Question, along with my reply:

Scott asks: I’m curious if you are aware that GMC Trucks with the Fuel Savings Mode had engine problems. I understand it’s from 2008 to 2013 years. I have a 2009 GMC Sierra 1500. It started using up oil before 100,000. My friend had two motors replaced before 100,000. The connection I think you’ll find interesting is that the problems were caused by Big Gov’t pushing Millage Standards! The Feds were pushing the Big Three to make their overall Fleet Milage Averages go up. GMC found a way to improve theirs by turning off 4 cylinders out of 8 when not needed to keep their trucks up at speed. Anyway, I can not explain why turn 4 cylinders off wrecks the motors, but if you dig around you’ll understand it better than I could ever explain it.

My reply: I am aware of this – and so are EPautos regulars, one of whom mentioned this issue the other day with regard to another manufacturer that, like GM (and Chrysler) uses cylinder deactivation technology to try to reduce fuel consumption during light-load/steady state cruising by “shutting down” some of the engine’s cylinders. I put “shutting down” in air quotes because the pistons are still going up and down in their bores; air is still being pumped by them – but no combustion is occurring because the fuel supply/spark has been shut off by the ECU (engine computer).

Potential problems that can develop as a result of this are as you’ve described. Cylinder/ring/valve sealing issues that result in premature or excessive oil consumption. It could be due to differential loading of the firing cylinders; it could be due to operating the “deactivated” cylinders without combustion occurring.

The real question, though, is – why do this at all? And – who benefits?

The fuel economy gains to the owner are slight; they are relevant only in terms of calculating so-called fleet averages – for purposes of CAFE (Corporate Average Fuel Economy) compliance. The fuel economy gains are almost certainly negated by the add-on cost of the system and the down-the-road costs, in the form of maintenance/repair/engine longevity.

The same, incidentally, is true of the latest idiocy – automatic engine stop/start – which almost every new car comes with now. The engine automatically shuts down whenever the vehicle isn’t moving, then restarts when the driver pushes on the accelerator pedal. This without question reduces the service life of the 12V starter battery due to the much more frequent start/discharge/recharge cycles and probably will decrease engine longevity due to wear and tear over time.

And, again, we can thank Uncle for this!

. . .

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  1. I knew the time Caddy tried it back in the 80’s it was a complete disaster. The computer wasn’t up to the task then.

    Hopefully they rotate the shutoffs to reduce the wear and tear a bit. But it sounds like something that still needs to be avoided. It’s going to be hard to avoid them all it seems.

    Darn, was liking the idea of a vehicle lasting (and being in decent shape) for fifteen years. It sure helps take the sting of the high prices of them.

  2. my 2007 Suburban also has this “feature”

    paid a pretty penny for a tuner to access the computer to turn it off.

    still burns some oil, so I’m wondering how much damage was done before I disabled it.


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