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Hybrid Vehicles Chevrolet Tahoe and GMC Yukon Hybrid Chevy Tahoe/GMC Yukon Hybrid
301 messages, Last post on Nov 23, 2009 at 10:58 AM
You are in the Chevrolet Tahoe and GMC Yukon Hybrid Forum. Your Host is pf_flyer
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I haven't read all the posts on this new tahoe, but I want to say something about the mechanical aspect of an 8 cylinder motor that shuts off 2 or 4 cylinders at any point during it's running time or it's heat cycle. Any internal combustion engine creates a lot of heat. All the parts of an engine go through a heat cycle where they expand and contract. A part that is round at room temperature is not round at 300 degrees. The reason I say this, is this; the cylinder bore that the piston goes up and down in is supposed to be round;;it's machined that way. The way it stays round is this,,there is holes drilled around the round cylinder which pass coolant or antifreeze through, thus evenly cooling the round cylinder bore that the piston lives in. In the chevy v8 the cylinders are set up in two rows of four. If you shut off 2 or 4 of these cylinders these cylinders will become unround or oval shape because of the heat that will be transfored from the cylinders that are working and creating a lot of heat. If you think the intake gasket leak problem on all chevy tahoes was bad wait until you see entire motors failing. I will say it will take about 50,000 or 60,000 miles and you will see severe engine damage and catistrofic engine failure....This motor is destined for the discovery channels'show "engineering failures"
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Replying to: pear69 (Nov 07, 2007 10:26 pm) I think your analysis has some good theory behind it. This is not a new way of trying to save gas. Honda has a V6 in their Odyssey and not sure what else with VCM. I have not read of any early failures yet. I am a keep it simple kind of guy so I would probably not be interested in such an engine. |
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Replying to: pear69 (Nov 07, 2007 10:26 pm) I don't think this will be a problem. The cylinders deactivate and reactivate continuously. I suppose in theory if one was going down a VERY long slope the cylinders might shut down for a few minutes, but in general the problem most people have always had with variable cylinder usage is that they don't shut down frequently enough to really help MPG. The moment extra power is required, even momentarily, the cylinders come back on line. However, this marks the first use in hybrid applications, so maybe they will shut down more. But considering the heavy weight of the Tahoe, it is very likely that all cylinders will be active much of the time. Also, we don't know how Chevy programmed the engine. It may well be that it is not the SAME cylinders shutting down - they may alternate, which spreads the heat around.
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Replying to: stevedebi (Nov 08, 2007 12:11 pm) I agree above, “Cylinder deactivation” is only on when the engine is in very light loading conditions (going down hill, cruising on the highway. etc). So heat being generated is pretty minimal. If the vehicle is towing or if the vehicle is accelerating, the internal engine software will activate all of the cylinders and the heat distribution in the engine will be some what even. . To this day I have not heard any latent catastrophic failures with the 5.3LV8 engines. I checked NHTSA and their defects website and it shows nothing. Also GM has a 100K mile powertrain warranty which covers the engine for that length of mileage. They wouldn’t guaranty the life the engine if they had some real test data that didn’t support it. If the engine fails you could always have it replaced. So I wouldn’t worry about it. I received official notice that GM has pushed out the Hybrid Yukon till early next year. Must be having some sort of problem. 
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Replying to: galvang (Nov 08, 2007 6:49 pm) (The GMC site doesn't list the weight of the Yukon, but I'm guessing it is 5500 lbs or maybe more...) I actually wonder if the "problem" isn't that this class of vehicle is too heavy for hybridization to provide a real benefit, other than shutting down the engine when stopped. That is what happened to the hybrid pickup - no real MPG savings. Of course the pickup had the 110v electric capability which may have been useful to some owners. Dual mode doesn't provide as much benefit to a large and heavy vehicle; the electric motors deplete very quickly due to the large amount of weight that has to be accelerated. With heavy vehicles the situation degrades to the point that it would take too much battery to provide enough boost, and then one has to remember that the battery adds weight and takes up room as well. AND hybrid components are complex and expensive. Some people assume that LiIon batteries will be the answer, but I'm not convinced that the recharging/heat problems of this technology will be overcome any time soon. |
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Replying to: stevedebi (Nov 09, 2007 9:21 am) That is the only thing I miss since selling my GMC Hybrid PU. I don't think the auto-stop saved enough gas to make any difference. It may have used more as there is a debate whether starting an engine uses more gas than idling for a minute or less. |
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Replying to: stevedebi (Nov 09, 2007 9:21 am) Yea, I could not find it in the product brochure but lists 7300Ibs for the gross vehicle weight for the regular Yukon, This includes passengers. The "problem" at this point may be minor such as battery or Hybrid motor or some other part availability (just guessing). If GM pushes out the introduction again then you know is something more serious. Problems like this always occur during the production of these complex vehicles or other items especially for the first year. I know I work in engineering, there always issues in complex projects like these and that's why the companies pay us the big bucks to resolve them. I rather see GM delay the introduction and produce it right then shipping out a lemon  . As for the Hybrid motors, perhaps it drains those Nickel Metal Hydride batteries faster than it was meant to. Lithium Ion batts are the way to go at least for the short term until a new exotic battery comes into fruitrition. The battery designer need to be careful though as lith ion batteries, if its not designed correctly, could explode or cause severe out gassing. Hence Toshiba and Dell Notebook recalls due to the lith ion batteries. Talk of polymer batteries might be the next thing but its all in paper. For Hybrid batteries its all about power and density and lithium ion seems to fit the bill at least for now. In some cases the Lith ion batteries can provide 50 percent more power in the same volume or space as with NiMH Batts. GM needs to get hot and release the hybrids.
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Replying to: stevedebi (Nov 09, 2007 9:21 am) The T/Y 2Ms save more fuel than either of these two 'classic' hybrids. My alternate viewpoint, assuming that the 2Ms work as described, is that all BoF SUVs should have the 2-Mode system installed mandatorily. Doing this will save our country far more fuel than any other single step other than banning SUVs altogether, which will not happen barring some obscene fuel shortage. Yes hybrid components are complex and expensive to replace but reliability across the board has increased dramatically. Hybrids are among the most reliable vehicles at every manufacturer. Prius, Escape, Civic all are good bets not to leave you in a lurch. |
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Replying to: pear69 (Nov 07, 2007 10:26 pm) I really don't see how this could be an issue. The engine is still water cooled and all cooling channels still get the same amount of coolant flowed through them whether they are firing or de-activated. The heat build-up / differences between cylinders will not be significant enough to make things out of tolerances. Look how much air cooled engines expand and contract without issues. Since this is a water cooled engine, it's true that the tolerances will be tighter, but then, the operating heat range is smaller as well, with or without deactivated cylinders. Plus, like other have said, they are de-activated for very short time periods and if the 'brain' is deactivating them, it means you are on a very low power situation so the other cylinders are likely barely working at all. Basically in a coasting or idling work mode rather than a "make power" mode like when accellerating. At which time, all cyclinders will be working anyway. This technology has been around for quite a while (in everything from 4 stroke auto engines to two stroke outboard boat motors) so it's nothing new. No doom and gloom needed. |
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Replying to: galvang (Nov 09, 2007 8:02 pm) Since Toyota has abandoned LiIon for the 2009 Prius Refresh, I would be shocked if GM solved the problems inherent with current LiIon batteries. |
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