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Thread: 2012 GMC Sierra- bad #7 cylinder

  1. #1
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    2012 GMC Sierra- bad #7 cylinder

    Took my 2012 Sierra into shop yesterday; running rough. Cylinder #7 plug is oil-fouled. I found out this is an issue with this engine.
    136,000 miles, truck is in excellent condition(otherwise); not covered under warranty. I was hoping to get 230,000-250,000 like my previous trucks.

    Do I spring for a new engine, or trade truck to a dealer or ...?

    Just asking for some thoughts, thanks

  2. #2
    greg Forster,

    I'd suggest first a compression test on all cylinders.

    This sounds as though the engine may need new rings. If it were the head gasket it would be a steam engine not oiled plugs. It's possible- not sure- that the engine would have to come out to do it, and if that's done, may as well do the heads. Under some circumstances, it may be possible to drop the subframe under the engine, take off the heads, undo the connecting rod bolts, hone the cylinders, and replace the rings. On older cars, this is not difficult, but on a modern car, taking off all the injection and emission control parts, and etc. may make it a big job to do at home. It's always tempting to do the work yourself, but in this example I think it would be a complex job with unforeseen problems- having to drop the suspension. engine subframe, breaking off cylinder head studs, breaking plastic sensors, having to replace all the hoses, replacing ignition modules, recharging the A/C upsetting the injection module, and etc.

    If the work needs to be done in shop, have an estimate or two and get an opinion- perhaps on a website on how long the useful life might be extended. If the problem is typical to that engine, it may only get three or four years. My sense is that he repair will be expensive, and may extend the life a few years, but if it's likely to recur and does, the Sierra will have a quite low value as the repair cost is such a large portion of the value.

    However, the value of that model in good order is still quite strong. Perhaps consider getting it going as well as possible, and trade in on a semi-depreciated newer one (2015-2016?) without known serious problems.

    Wow, that's a very tough call, because a 2012 Sierra are still worth a good amount. If it's a daily work vehicle, and it can't be out of use for three weeks or so, a quick change to a newer one, not having this known problem, with an acceptable loss =med blue book minus the repair estimate, may be the best choice. The decision depends on the estimate for the work and how long it's likely to stay fixed.


    Alan
    Last edited by Alan Caro; 08-02-2019 at 10:27 PM.

  3. #3
    I would get an estimate, fixing would probably be way less than buying new. Having looked recently, the price of new trucks are very pricey. In NJ since your vehicle has over 100K miles, a dealer can't resell, so the value you get would be lower, where you live may be different.

  4. #4
    Is the oil coming past the rings, or around the valve stems? Is drain hole at back of head open? A blow down gauge will tell you more about the shape of the rings than a compression test. If it needs valve steam seals, that can be done in the truck. If it needs rings, I would look at a "crate motor." instead of working on that one. It's easy to drop between 3 -5 K on an engine replacement. Check "Rock Auto's" web site and you can see what a reman engine will cost you.
    Last edited by Bruce Wrenn; 08-02-2019 at 9:14 PM.

  5. #5
    Depending on how well you like your current vehicle, and the actual cost per-mile you're willing to pay for transportation--- consider that borrowing $57,600 for a new truck for 6 years at 4% will run you $900 a month. A $3000 engine repair is roughly equal to 3-1/2 new truck payments...
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  6. #6
    Quote Originally Posted by Kev Williams View Post
    Depending on how well you like your current vehicle, and the actual cost per-mile you're willing to pay for transportation--- consider that borrowing $57,600 for a new truck for 6 years at 4% will run you $900 a month. A $3000 engine repair is roughly equal to 3-1/2 new truck payments...
    It's a personal decision obviously, but I was thinking the very same thing as you were, Kev.

    Greg, I'd figure out the cost of a truck equipped the way you want it. (Do you want a cheap one or a high end one?) Then, do the math like Kev did. If you think the Sierra is solid enough to meet or exceed the break even point, you could delay replacing that truck a while if you want.

    Good luck!
    Fred
    "All that is necessary for the triumph of evil is that good men do nothing."
    - Sir Edmund Burke

  7. #7
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    Quote Originally Posted by greg Forster View Post
    Took my 2012 Sierra into shop yesterday; running rough. Cylinder #7 plug is oil-fouled. I found out this is an issue with this engine.
    136,000 miles, truck is in excellent condition(otherwise); not covered under warranty. I was hoping to get 230,000-250,000 like my previous trucks.

    Do I spring for a new engine, or trade truck to a dealer or ...?

    Just asking for some thoughts, thanks
    Hey Greg, I have a 2013 Silverado V8 and am curious if this vehicle is potentially affected with the same issue. Can you post a link to some of the info you found that clued you in to this issue?

  8. #8
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    If you buy a remanufactured engine try to get one with better rings in it if that is the problem. If it's valve seals I would get it fixed but it is probably rings.
    Save the ols engine and repair it with better rings for the next time around.
    If I had the time I would do the rings myself.

  9. #9
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    Quote Originally Posted by greg Forster View Post
    Took my 2012 Sierra into shop yesterday; running rough. Cylinder #7 plug is oil-fouled. I found out this is an issue with this engine.
    136,000 miles, truck is in excellent condition(otherwise); not covered under warranty. I was hoping to get 230,000-250,000 like my previous trucks.

    Do I spring for a new engine, or trade truck to a dealer or ...?

    Just asking for some thoughts, thanks
    in your research did anyone mention what were the problems causing oikl fouling?

  10. #10
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    "Remember back in the day, when things were made by hand, and people took pride in their work?"
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  11. #11
    Quote Originally Posted by Bruce Wrenn View Post
    Is the oil coming past the rings, or around the valve stems? Is drain hole at back of head open? A blow down gauge will tell you more about the shape of the rings than a compression test. If it needs valve steam seals, that can be done in the truck. If it needs rings, I would look at a "crate motor." instead of working on that one. It's easy to drop between 3 -5 K on an engine replacement. Check "Rock Auto's" web site and you can see what a reman engine will cost you.
    Agreed, have more diagnostics done.

    BTW, if you do go for a reman engine, be aware that once you're past the warranty period, if you have more engine problems, the "rebuildability" of a reman motor is rather questionable. The remanufacturing process is typically one of "pushing the tolerance specs to the limit", as part of "let's just push all these pigs out the door", and there is often nothing left to give, in the future. Golden rule, never try to rebuild a reman.

    It might be a better idea to simply have the engine repaired, if there's nothing else wrong with it, even if it costs the same or slightly more than a reman. (And you're going to have to do a remove_and_replace in either case, so take that into account.) Methinks that's your best bet for getting the desired 200k+ miles out of it. Provided you can find a good rebuilder (not always straightforward.) IF the motor requires that.

  12. #12
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    Quote Originally Posted by Dave Lehnert View Post
    So they are saying that excessive oil consumption would be a clue as to this. I wonder if the OP noted excess oil consumption on his vehicle and for how long.

  13. #13
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    I'd go with a factory rebuilt motor. The idea that a rebuilt motor is marginal has no basis in reality. Rebuild kits with over-sized journals, mains and pistols are state-of-the-art for a century. Any parts that are out of-of-spec are discarded. There's plenty blocks, cranks, rods, etc; factory rebuilds are as good as new and maybe better because the casting are relieved from use.

    On the other hand, pulling a motor apart to replace a single piston/ring assemble makes no sense to me. No chance to hone, just slap in another problem and repeat in 10k miles. No thanks, for all the effort I'd choose a factory spec rebuild. Best way to make another 130kmiles trouble free. It's that or trade it in.

  14. #14
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    Either rings or valve guides they are both repairable for far less then a rebuilt engine.

  15. #15
    Quote Originally Posted by Eric Danstrom View Post
    I'd go with a factory rebuilt motor. The idea that a rebuilt motor is marginal has no basis in reality. Rebuild kits with over-sized journals, mains and pistols are state-of-the-art for a century. Any parts that are out of-of-spec are discarded. There's plenty blocks, cranks, rods, etc; factory rebuilds are as good as new and maybe better because the casting are relieved from use.

    On the other hand, pulling a motor apart to replace a single piston/ring assemble makes no sense to me. No chance to hone, just slap in another problem and repeat in 10k miles. No thanks, for all the effort I'd choose a factory spec rebuild. Best way to make another 130kmiles trouble free. It's that or trade it in.
    OEM rebuilds _might_ be better than aftermarket, but still...

    If you think that an aftermarket remanufacturer is going to go in and measure everything that is worn in a core they receive and blueprint it to least-invasive factory spec, you've been drinking the advertising brochures. ;^) What they're going to do is to spec it to the commonality of the most-damaged core they can reuse, and build to that standard (on a production line.) That means little or no further margins. (Not intended to be serviced further.) They're a business, and they're in it to make money. Especially at the prices many of them are charging (i.e. low not high.)

    In this case, the ring quality is an isolated known problem. If a motor has bad rings, and that's all, you'd be crazy to do a full blueprint rebuild of everything else in the motor. Either that or made of money. (You'd be advised to put in better rings this time, though.) At least in this case, if something else goes wrong, you have something to work with.

    BTW, I might be worried that a _factory_ reman would put in the OEM rings that caused the trouble in the first place, in which case your prophecy of shortened life might come to pass. Maybe, maybe not. If the warranty is only a year, what does the OEM care.

    Aftermarket remans are for those people who want the vehicle to run correctly until they can sell it. That is all.
    Last edited by Doug Dawson; 08-04-2019 at 11:44 AM.

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