Warning: Bad to bump start and skip gears - Page 5 - Fuelly Forums

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Old 05-30-2007, 11:43 AM   #41
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IMO, you should use the oil weight recommended by the manufacturer. You're not going to notice a difference if you go from 20 to 30. You may think you do, but you don't.

Why would coasting with the engine off cut down on lubrication? Once the engine warms up, oil is everywhere. You'd have to coast for an awfully long time to affect lubrication.

Bump starting rear wheel drive isn't much different. I'm replacing my transmission and motor mounts soon. I'd highly suggest that you guys look into getting polyurethane mounts or inserts. It may give a little more vibration, but that's just a reminder of the power going to the wheels rather than the excess damping provided via the stock mounts. Obviously, rev match as much as possible.

A bump differs from a hard shift in that you are connecting something spinning at relatively high rpm to something that isn't spinning at all. It's a difference in the magnitude of the acceleration/deceleration.
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Old 05-30-2007, 11:58 AM   #42
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Quote:
Originally Posted by DrivenByNothing View Post
You're not going to notice a difference if you go from 20 to 30. You may think you do, but you don't.
I agree you'll be unlikely to be able to measure it, but it's still real.

I read a Ford document linked at bobistheoilguy.com which explained their decision to go from 5w30 to 5w20 in one vehicle. The fuel savings were laid out. The difference was very small < 1%, if I recall. (Didn't bookmark it - sorry.)
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Old 06-03-2008, 10:31 PM   #43
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Just a newbie and could have missed something.

Doesn't bump starting slow your forward energy? And apparently just when you are needing to do just the opposite?
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Old 06-04-2008, 06:24 AM   #44
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Boy, talk about bump starting an old thread....

I agree, bump starting isn't free, it uses energy too. I suspect that it's more efficient, since you're converting linear kinetic energy to rotational kinetic energy (at the road-tire interface) and then keeping it as rotational kinetic energy to start the engine. That's instead of use electricity to do it, which means you have to recharge the battery, converting kinetic energy to electricity, storing it, and then converting it back. So many conversions will undoubtedly be less efficient.

However, it's still not worth it to me on my leased, warrantied car with a clutch that costs $3000 to replace (and of course wouldn't be covered under warranty) and the manual says not to do it and even electric-starting causes the car to make an abnormal warning beep that I don't know what it means...

It does seem to be working well for those early-90s Civic VX guys though.
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Old 06-04-2008, 07:04 AM   #45
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That warning beep is probably your seat belt not connected warning - buckle up before starting the engine!
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Old 06-04-2008, 07:28 AM   #46
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I think one should carfully consider the impact, potential cost, and their ability to remedy a problem before doing much EOCing.

I honestly don't think that there is significant wear to the clutch in bump starting in a high gear, but I am also prepared and well versed in replacing such things. Likewise, key starting could cause additional wear on the starter and potentially the flywheel. A burned out starter is relatively nothing to replace in most cars, but a chipped tooth on the flywheel is a clutch job+flywheel replacement.

So is there really a payoff in the long run? Only time will tell for most of us.
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Old 06-04-2008, 08:30 AM   #47
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Quote:
Originally Posted by JanGeo View Post
That warning beep is probably your seat belt not connected warning - buckle up before starting the engine!
Nope, I was wearing the seatbelt. I've pretty thoroughly analyzed it and it's nothing like the seatbelt warning. I was driving along, decided to try EOC, and when I restarted it was three long beeps, a pattern the car has enver made under any other circumstance. I asked on golfmkv.com (vw forum) and, after a bunch of moral judgements from people who believed I was lucky not to cause the end of the world by EOCing, nobody knew what it was.

I may try again soon with Vag-Com cable/software hooked up to gather data, and get video while I'm at it so people can see the empty danger-free road where I try it and I can get audio of the beeps.
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Old 06-04-2008, 08:33 AM   #48
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Maybe it's saying "Duh, methinks the speed sensor has failed, 'coz somehow we seem to be moving at 30mph, when my most excellent german engineers who know everything and can forsee all possible circumstances have convinced me that when you start my engine it should be reading ZERO!!!!1111"
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Old 06-04-2008, 09:07 AM   #49
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Maybe it's saying "Duh, methinks the speed sensor has failed, 'coz somehow we seem to be moving at 30mph, when my most excellent german engineers who know everything and can forsee all possible circumstances have convinced me that when you start my engine it should be reading ZERO!!!!1111"
werd. it's probably there just to scare people into not bump starting. "OMG whats that noise, its never done that before!?"
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Old 06-04-2008, 09:23 AM   #50
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It's almost certainly something like that, though probably not the speed sensor, as I turn it to "On" immediately after killing the engine so I still have gauges and unlocked steering. If I owned the car and it was out of warranty I would certainly just go ahead and do it, but it's a lease and I am not willing to risk the computer recording the event and then it costing me money later. If I ever get comfortable with it, I will definitely save some decent MPG; I get some nice long glides.
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