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G350

Original Poster:

382 posts

49 months

[news] 
Thursday 3rd March 2011 quote quote all
Anybody here managed to bump-start a car with an automatic gearbox apart from me and 530dTPhil?

530dTPhil said:
I did it many years ago with a Beetle automatic. The handbook said tow to about 25 mph and engage drive -- it worked! Never tried it on any conventional automatic though.
^from the "Correct way to push-start a car" thread.

G350 said:
Free-wheeling in neutral with the engine off down a very long stretch (>10 miles) of deserted desert dual carriageway in the middle-east, put the ignition on and just snuck it into D and the engine started in a very smooth and undramatic way. Easy peasy. Not tried it in my other automatics.

1995 model Jeep Grand Cherokee, full-time 4x4, 4-litre 6-cyl, 4-speed autobox.
Most driver handbooks warn against it, some threatening serious gearbox damage. Also due to the probable speed involved it is possibly not the safest thing to be doing.

But has anyone else tow-started or bump-started a car with an auto gearbox? What speed? Any damage/problems?

Welshbeef

18,249 posts

84 months

[news] 
Thursday 3rd March 2011 quote quote all
But you shouldn't bump start even manuals since catalytic converters were introduced as the unburnt fuel kills it and a new cat is not cheap and if exhausted is an mot failure.

Don't bump start cars

G350

Original Poster:

382 posts

49 months

[news] 
Thursday 3rd March 2011 quote quote all
Welshbeef said:
But you shouldn't bump start even manuals since catalytic converters were introduced as the unburnt fuel kills it and a new cat is not cheap and if exhausted is an mot failure.

Don't bump start cars
That's a good point. My Jeep was a leaded-spec car with no cat.

Here's what it says in my 2011 BMW 3-series handbook:

...With a catalytic converter, the vehicle should only be tow[-started] when the engine is cold; with an automatic gearbox, tow-starting the engine is not possible...


supersingle

2,772 posts

105 months

[news] 
Thursday 3rd March 2011 quote quote all
Welshbeef said:
But you shouldn't bump start even manuals since catalytic converters were introduced as the unburnt fuel kills it and a new cat is not cheap and if exhausted is an mot failure.

Don't bump start cars
A cat can take quite a bit of fuel before it breaks. I drove over a hundred miles with a dodgy coil with one cylinder pouring neat fuel into the exhaust. Cat was fine as were emissions at the last MOT.

Welshbeef

18,249 posts

84 months

[news] 
Thursday 3rd March 2011 quote quote all
I guess there is tolerence with regard to bump starting manual cars with catalytic converters - BUT you don't know how many times you can do it and how many times it's been done before and also with age it may be the straw that broke the camels back.

Get breakdown cover instead.

With auto's firstly if the engine is running and let's say you accelerate up to 50mph push it into N and then let it coast down to 40mph and push it into D? Anyone tried anything like that?
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G350

Original Poster:

382 posts

49 months

[news] 
Thursday 3rd March 2011 quote quote all
Welshbeef said:
With auto's firstly if the engine is running and let's say you accelerate up to 50mph push it into N and then let it coast down to 40mph and push it into D? Anyone tried anything like that?
Yes, loads of times with the G-wagon, Forester and others. No probs. It just slips back in to gear - bit like letting the clutch out in a manual.

Not tried it in the E91 (yet) as its only done 000200 miles wink

Why you ask? confused

dylan0451

1,036 posts

77 months

[news] 
Thursday 3rd March 2011 quote quote all
i don't see how the cat is any more or less washed with fuel by bump starting than tow starting, or even jump starting with the engine being spun by the starter?

i think it's maybe just H+S because someone in america managed to get run over by their own car or something?

like the 'bump starting a car can skip teeth on the cambelt and destroy the engine' bks

richw_82

856 posts

72 months

[news] 
Thursday 3rd March 2011 quote quote all
Once successfully, once not so successfully. The success was an old series 3 XJ6, down a rather large hill with no traffic, as a last resort after it wouldn't start. No idea what I would have done with a two ton Jag doing 35mph(ish) if it hadn't fired up by the time I got to the bottom, as they're a cow to deal with when you don't have power steering or servo brakes working.

The one that went wrong... a 1991 Ford Granada. Spurred on by the way the Jag coped a few years earlier, I tried it with the Granada when it misbehaved. Engaging "drive" at about the same speed resulted in a large bang, then crunch tinkle grind. The auto box was not happy at all.

Rich

Edited by richw_82 on Thursday 3rd March 15:12

russell_ram

188 posts

117 months

[news] 
Thursday 3rd March 2011 quote quote all
Success in bump starting an auto will entirely depend on the gearbox. If it doesn't have a pump on the output shaft then it won't have any line pressure with which to engage a gear - no amount of towing will get the engine to turn over. Most modern autoboxes have their HP pump on the input shaft so it won't work. I could envisage that a electrically/solenoid controlled box would work also. I am obviously excluding the latest generation of stop/start (engine) hybrid autos though - they mostly have some kind of hydraulic accumulator to enable the gearbox to continue work without the engine running.

Russ

editted for grammar (which is still probably rubbish).

Ozzie Osmond

16,221 posts

132 months

[news] 
Thursday 3rd March 2011 quote quote all
russell_ram said:
Most modern autoboxes have their HP pump on the input shaft so it won't work.
^^^^ This. If the pump's not running the transmission can't function.

Fish981

875 posts

71 months

[news] 
Thursday 3rd March 2011 quote quote all
Ozzie Osmond said:
russell_ram said:
Most modern autoboxes have their HP pump on the input shaft so it won't work.
^^^^ This. If the pump's not running the transmission can't function.
And isn't there an issue with gearboxes that have the HP pump on the output shaft? I'd heard rumours sitting stationary for too long with the car in gear can fry the 'box.

seagrey

385 posts

51 months

[news] 
Thursday 3rd March 2011 quote quote all
Some of the older borg warner/triumph/bl auto boxes you could tow or bump start but you had to chuck a couple of litres of extra fluid in first.
I personally wouldn`t attempt it on any modern auto box.
on the subject of cat damage by bump starting its no worse than when you crank the engine over before it fires.
Unless it fires instantly,its still pumping fuel into the cat.
And certainly no worse than sitting there cranking a non starter over for ages if for instance the coil pack failed.

EarlOfHazard

877 posts

44 months

[news] 
Thursday 3rd March 2011 quote quote all
Old auto Jags could be be bump started, there is a secondary pump in the old Borg Warner gearbox. You need to be going over 30mph though! yikes

Jimmyarm

1,115 posts

64 months

[news] 
Thursday 3rd March 2011 quote quote all

Never tried to bump start anything with an auto box.

I'd be wary about bump/tow starting anything with a floating crankshaft pulley for the cambelt. I may know someone that did this to a 2003 renault megane diesel and it resulted in 6 of the valves bending themselves, 2 valve guides cracking and the camshaft journals splitting in half eek

tr7v8

4,727 posts

114 months

[news] 
Thursday 3rd March 2011 quote quote all
My late father ran a fleet of 150 Mothers Pride vans which were BMC 2.2 taxi diesels with BW 35 autos. Exciting as a 14 year old being dragged around a yard at 25-30MPH especially when it was icy or snowing! These were dual pumped so would tow start but most boxes as people have said only have pumps on the input shaft, so cannot be tow started. Unless a 100% sure it can be tow started DON'T as you'll destroy the box if you try. The cat won't worry as the minute the engine starts it'll light up any excess fuel anyway.

Pentoman

4,434 posts

149 months

[news] 
Saturday 5th March 2011 quote quote all
Done it on merc 190E.
Downhill circa 30mph.

OllieWinchester

5,235 posts

78 months

[news] 
Saturday 5th March 2011 quote quote all
Saw it done at banger racing, quite low speed too.

infradig

976 posts

93 months

[news] 
Saturday 5th March 2011 quote quote all
As mentioned in previous posts old Borg Warner 35 and 65's had to be going quite fast-once started a mates Rover 3500 by towing it up to about 80 with a MkIV Zodiac probably a bit ott but funny when you're 18.

NHK244V

2,144 posts

58 months

[news] 
Sunday 6th March 2011 quote quote all
Lots of times over the years, usually in the P6 rover, when the fuel runs out you pull the reseve lever out and if your doing over 30 it bumps starts, jags and mercs as well, last time was last week in a toyoya spacecruiser.

G350

Original Poster:

382 posts

49 months

[news] 
Tuesday 8th March 2011 quote quote all
Thanks all for the input. It's been a good read.
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