Warning: Bad to bump start and skip gears

[budomove]

Posted these questions on HT and got the following response.
Just a heads up.



Is it bad to shift from 1st into 4th, assuming you are not revving 1st too high. My gears are really long...4spd std?

I recommend either shifting to neutral and letting out the clutch to rev match fourth gear or push in the clutch, shift 2-3-4, and let out the clutch. It is easier on the synchros.

Is it bad to coast in neutral?

It is OK to coast in neutral. Make sure the clutch is out to keep the input shaft spinning. This ensures lubrication. I usually coast for shorter periods by depressing the clutch with the transmission in gear. For longer periods, I shift to neutral.


Is it bad to coast with engine off, and bump start?

Don't bump start. You can really stress the axles. If you do bump start, use the highest gear. Coasting with the engine off also cuts your engine lubrication. So, you are restarting each time. It is not as bad as a cold start, but I don't recommend it.

[JanGeo]

Bump starting is a matter of how stiff your engine is and what gear you are in. The sticksion of a stopped engine may be greater than one that is rotating. With my Scion on Synlube it can bump start at 2mph in 2nd gear so not much of a wack to the engine mounts.

[Snax]

In our 5, a bump start at 10-15 mph is about like running over a cat. Not much drama to it - so long as you aren't the cat.

There is an issue with the power steering coming back online however. Apparently the control system doesn't like to re-engage it until the revs drop for several seconds. While that's not really an issue at higher speeds, it's not something I think I will be doing much of around town.

[DrivenByNothing]

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.

[MetroMPG]

Originally Posted by DrivenByNothing

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.)

[gungadin]

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?

[theholycow]

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.

[JanGeo]

That warning beep is probably your seat belt not connected warning - buckle up before starting the engine!

[theholycow]

Originally Posted by JanGeo

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.

[Snax]

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.