Bump Starting Vehicles.

George7941 · Mar 24, 2007

"Trying to start your vehicle by pushing or pulling will not work, and it could damage your vehicle".

This is an exact quote from the Owners' Manual for a 2006 GMC Sierra(p5-53 for those who have this manual). There is no mention that this applies to automatics only.

I let my truck roll down a hill and let the clutch out gently and the engine started up with no difficulty. So why is GM making such a blanket statement which I do not think is true? Why do they say "will not work" when it did in my case? Am I missing something? Only explanation I can think of is that GM forgot to mention 'automatics only'. The damage they refer to must be damage resulting from the vehicle being pushed or pulled e.g. bumper damage.

surfstar · Mar 24, 2007

?? Ya got me.

I had to push start my car on my own when the starter was intermittantly going out. Still runs great at 215k miles (original clutch too!).

ewetho · Mar 24, 2007

For those with a dead battery you can not push start a modern car without much effort and you could mess stuff up.

If you had a car such as some of the Crown Vic you could get the alternator to self excite at about 3500 RPM and then at least it would attempt to start charging. Then when you got voltage up enough with the dead battery it might light off.

Otherwise if the battery is dead your in trouble. Now if you just lost a starter and had a good battery then a push start is just fine. Heck they are using the Generator/Motor as the starter on those.

George7941 · Mar 24, 2007

Also, I will add, automatics could get damaged internally from the tranny oil pump not working when the engine is not running. You will have to make repeated attempts at push starting with an automatic for this to happen, you would think somebody would give up after a couple of attempts.

mechtech2 · Mar 24, 2007

Some automatic trannys are not internally oiled when the engine is not running.

H2GURU · Mar 24, 2007

As an experienced "bump starter" I can tell you that it should only be done on manual transmission vehicles and really only as a last resort. Reason being... it is very simple to bend and break the VALVES in the engine during this procedure.

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George7941 · Mar 24, 2007

"it is very simple to bend and break the VALVES in the engine during this procedure."

Would you please elaborate? How would you end up breaking the valves?

Gary Allan · Mar 25, 2007

Quote:

"Trying to start your vehicle by pushing or pulling will not work, and it could damage your vehicle".

You should have also quoted a few sentences on either side of that one. It should have been accompanied by some mention of a dead battery.

I'd be interested in learning any other reason why it cannot be done. Now if you're side stepping the clutch at a good clip, I'd say you could strain some of the mounts and such

I don't believe any automatic has had a rear pump since the very early 60's. Those, if you could get it going fast enough, could be push started. I think a 61 TorqueFlite had a rear pump. All these were surely gone by the mid/late 60's.

JakeR22 · Mar 25, 2007

Bump starting a manual tranny vehicle does the same thing as what the starter does, turns the engine over...

No valve damage would be done, ever.

Gary Allan · Mar 25, 2007

Quote:

Bump starting a manual tranny vehicle does the same thing as what the starter does, turns the engine over...

Not quite. The starter has a limit to the torque it can apply and limits to the speed that it can attain. Once the engine is started (which will be the first thing most of you will point out to support "it's the same"), the stress is reversed from the crank pushing everything ..to it being pushed (turned -whatever). This is opposed to the mass of the car (potentially - if the "side step" technique is used) spinning the crack to a high speed from a standstill. Think of it as the difference between hitting a redline on an engine ..and "over winding" a bus engine by down shifting at too high a speed (this will require a tiny bit of adaptive thought here to enable you to connect the dots and understand what I'm trying to say).

Now the valve thing does leave me

..but could have something to do with the aforementioned "difference(s)".

eljefino · Mar 25, 2007

This warning came out when catalytic convertors came out because, at the time, a carburetor could suck all sorts of fuel down without spark if conditions were right.

My sister's late-80's nissan sentra included bump start directions, but only for use with the diesel engine. (!)

One should have a not completely flat battery to try this: a few volts will be required to energize the field circuit of the alternator. Once that is accomplished the car will pull itself to life by its bootstrings.

The newest junk with theft/passlock keys or other logic might adamantly refuse to catch without a proper "crank" signal. And this could vary from car to car. Suprised the GM mentioned above doesn't have this. Vehicles notorious for remote car starter problems would have the worst times.

Anyone who's enjoyed real success roll starting will use 3rd or 4th gear at 5-10 MPH for better mechanical advantage. This won't overrev the engine by any stretch, in fact it will be a lugging idle.

Sliding off topic, I had a junk 1994 Saturn SL2 that roll started fine but the ABS light would be on after every roll start. Jump it and the ABS remained happy.

Sliding further, the shop manual for my dad's 1993 Ford Escort mentioned a special mode with stronger/longer coil dwell if it noticed RPMs without a crank signal, meant to help a persumably weak battery. Am sure the owner's manual included the admonition not to try it.

Lots of good hints in the original FSM.

George7941 · Mar 25, 2007

Quote:

Quote:

Bump starting a manual tranny vehicle does the same thing as what the starter does, turns the engine over...

Click to expand...

Not quite. The starter has a limit to the torque it can apply and limits to the speed that it can attain. Once the engine is started (which will be the first thing most of you will point out to support "it's the same"), the stress is reversed from the crank pushing everything ..to it being pushed (turned -whatever). This is opposed to the mass of the car (potentially - if the "side step" technique is used) spinning the crack to a high speed from a standstill. Think of it as the difference between hitting a redline on an engine ..and "over winding" a bus engine by down shifting at too high a speed (this will require a tiny bit of adaptive thought here to enable you to connect the dots and understand what I'm trying to say).

Now the valve thing does leave me

..but could have something to do with the aforementioned "difference(s)".

You are taking it to the extreme. One can reasonably assume that the bump start is being done prudently and that the clutch is engaged gradually and that the engine will not be spinning anywhere near its redline.

You are right about the dead battery. The quote is in the section on jump starting the truck. In the majority of instances when jump starting a vehicle the battery is not totally dead, it will have enough power to operate the ignition system, it just cannot handle the starter load. I just find the GM statement misleading

George7941 · Mar 25, 2007

"The newest junk with theft/passlock keys or other logic might adamantly refuse to catch without a proper "crank" signal. And this could vary from car to car. Suprised the GM mentioned above doesn't have this. Vehicles notorious for remote car starter problems would have the worst times."

Eljefino. I think you came up with the right answer and a possible explanation of the GM statement! The Owners Manual assumes all Sierras have the Passlock keys (my truck is a stripper truck and does not have a Passlock system even though the Manual insists it does). If I had the Passlock system then I, possibly, would not be able to bump start my truck, but I can and that makes me glad I do not have the Passlock system. I still have not gotten around to installing a hidden kill switch but I will, soon.

I can think of at least one instance with my previous truck (1986 Ford F250) where I would have been stranded had I not been able to bump start my truck. The starter failed but, since I was parked on an incline, I merely had to let the truck roll a bit and let the clutch out. I always kept a spare starter for that truck at home since the starter kept going out on me every few years, like clockwork. I think the Big Six 300 engines had weak starter motors

Gary Allan · Mar 25, 2007

Quote:

You are taking it to the extreme.

For demonstration purposes only. You'll note that I took both examples to the extreme and hoped ..prayed that you also saw this advice attached to it.

Quote:

this will require a tiny bit of adaptive thought here to enable you to connect the dots and understand what I'm trying to say)

Redline - high speed - not so bad
Overwinding - high speed - very bad

Now if you recall the multitude of tests that we've all taken ..Big Square is to Big Circle ...as little square is to little circle ......

Starter turning - not bad at all
Yanking your crank from zero to ??? in next to no time flat with the mass of the car driving it- who knows??

Also, can you see GM, Ford, DC ..or any other manufacturer attempting to describe "being done prudently and that the clutch is engaged gradually ..." in their manual

surfstar · Mar 25, 2007

I'm trying to conceptualize a bump start getting the engine to redline ??

Exactly how fast are we pushing this car/truck? My car redlines in first gear at over 30mph. Try running that fast, let alone pushing a car that fast. Anyways, I use 2nd to bump start, as its easier on the clutch.

Gary Allan · Mar 25, 2007

Quote:

I'm trying to conceptualize a bump start getting the engine to redline ??

For those who "scan read" (like I do)

Quote:

this will require a tiny bit of adaptive thought here to enable you to connect the dots and understand what I'm trying to say)

Quote:

Big Square is to Big Circle ...as little square is to little circle ......

Now - in a 3 step process to enlightenment of how to connect the dots.

Redline - high speed - not so bad
Overwinding - high speed - very bad

Starter turning - not bad at all
Yanking your crank from zero to ??? in next to no time flat with the mass of the car driving it- who knows??

So ...as you should see now ...bump starting has nothing to do with redlining your engine. It merely gives you the comparative difference between (for those capable of adaptive/abstract vision - apparently not at all common

) between using your starter and having the engine catch and revving to whatever speed ..as opposed to slamming the crank from zero to whatever speed and having the rods and pistons "flaying" around without the normal compression/vacuum forces governing it.

This may have absolutely nothing to do with potential damage from bump starting. This was to show (again, if you're not "scan reading) the DIFFERENCES between using the starter and using the mass of the vehicle to "bump start" the engine. THIS IS THE ESSENTIAL INFORMATION HERE.

I really need to see where I lose everyone in my posts. Now I know I can get out there ...but I even did it pony style and still had stuff missed as though it was invisible.

Quote:

Exactly how fast are we pushing this car/truck?

Who says that anyone (out of the vast number of people who may do this) is "pushing" it? Suppose they purposely park it on a hill and side step the clutch @ 30 mph and do it while in 1st or 2nd gear???

..and...again....where does your average jane/joe learn this preferred technique? Not in the owners manual ..so does uncle Bob take them out and demonstrate the bump start technique to assure that they do it properly??

For anyone who still sees me equating bump starting to redlining the engine ....never mind ..move on ..there's nothing to see here

mechtech2 · Mar 25, 2007

No one is going to bump start their car unless it is an emergency, or something like that. So it is OK to do so without fear of harming the engine.
Bending valves???

Crashbox · Mar 30, 2007

Bending valves????? That's a new one to me also!!!

I've pop-started my '95 Civic on occasion just to test it- about three or four MPH is all I need.

I think some of the Ford automatics still had rear (driveshaft-driven) pumps in them fairly late in production. The GM Powerglides had rear pumps in them and my old '65 Dodge Coronet 383 4-bbl had the Torqueflite B trans (last year for it) with a rear pump also.

They should have made a law to mandate rear pumps in automatics or- better yet- outlaw self-shifting transmissions entirely hehehe...

1040 WreckerMan · Mar 30, 2007

I can't see bump starting bending valves unless there is already an existing problem with the engine. There are a few, albeit very few, rear pump automatics hanging around. For the most part you'll not see rear pumps, the vast majority of automatics are all front pump and won't turn the engine fast enough to fire it unless some ungodly road speed is achieved.

In most cases, rear wheel drive, a u-joint or driveline will fail long before engine damage will occur. There are always exceptions of course, but you'd really have to try to hurt the engine by bump starting it.

brianl703 · Mar 30, 2007

Quote:

The newest junk with theft/passlock keys or other logic might adamantly refuse to catch without a proper "crank" signal. And this could vary from car to car. Suprised the GM mentioned above doesn't have this. Vehicles notorious for remote car starter problems would have the worst times.

My 2006 Saab 93 is capable of being push-started. I stalled it once and it was still moving (don't ask how I managed that one) so I let the clutch back out and it started right up. (I immediately pushed the clutch back in). It's got all of the anti-theft stuff in it and I'm only aware of one person ever having figured out how to add a remote starter to one.

Bump Starting Vehicles.

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