Can you bump start a new Diesel motor?

[KybraBoss Junior Member Find all posts View Profile Close KybraBoss]

In the past I wouldn't have thought twice about bump/push/pull whatever you like to call it starting a diesel motor, on my older trucks I even made sure that I could get a crank handle in for just in case.
But looking at all the fandanglery under the bonnet of the new 120 common rail is it safe to try... will it work or am I just going to tear apart the motor, gearbox or both?

[01Rod Junior Member Find all posts View Profile Close 01Rod]

Re: Can you bump start a new Diesel motor?

Short answer is no...

Because the electronic fuel injection, electric fuel pumps etc.
require a minumum threshold voltage to operate. (above 10.50V)
you will find you will pop the clutch and nothing will happen.
(this also applies to petrol vehicles as well)

In saying that if the battery was only down a little bit it might work. but.......

They say you should never clutch start a Diesel vehicle anyway..
because of the high compression in the engine it can cause damage to the drive train.

In saying that I know alot of people that have clutch started older diesels..
and I have seen a couple with damage to driveshafts as a result too...(twist)

Hope this helps
Rod

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Can you bump start a new Diesel motor?

I say “yes you can” and it’s worth a shot if you have no other choice.

Diesel cars can actually be easier to start than petrol especially if hot.

A diesel car often has a bigger battery due to powerful starter motor being required. The starter motor consumes a lot of the power the battery can provide in a short period of time but the battery will still often have enough reserve power to heat up glow plugs or power the engine management even though it can't turn over the engine.

I don’t see how you could damage the drive train unless you are being reckless.

Say, 2nd gear, ignition on, slowly let out the clutch (don’t dump it)

Look what happens when you do a “Key” start off road... How easy do they start!!! Flick the key and the hill does the rest!

Mick

[01Rod Junior Member Find all posts View Profile Close 01Rod]

Re: Can you bump start a new Diesel motor?

Just to clarify...

It will depend on the battery condition....
the minimum threshold voltage is approx 10.40volts.

If it is below that (eg left the lights on and the battery is fully discharged)..then good luck... if its not then it will possible work..

There is another reason for not clutch starting the vehicle if the battery has failed.. but that is about voltage spikes and avoiding damage to the electronics...
main reason being is that the battery not only starts the car but it also absorbs any voltage spikes or load dumps... if the battery is flat or faulty then it may not be able to protect the car in the event of a spike, thus leaving the car unprotected if a voltage spike should occur. Same theory applies to jump starting the vehicle...

As for the drivetrain damage....
Thats what I was taught as an apprentice mechanic.. never clutch start diesels..
and I know thats what the auto clubs like RACQ also train there patrolmen..
I have seen at least two vehicles where damage was caused to the tailshaft when trying to clutch start the vehicle....
and I know of one other suspected diff failure that was attributed to the "clutch start".

It's a bit like a voltage spike.. it wont happen everytime, for some maybe never. But it does happen.

I am happy to explain further if you would like me too...

Rod

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Can you bump start a new Diesel motor?

Fair enought about if the battery voltage is to low to fire up the engine management.

and I know thats what the auto clubs like RACQ also train there patrolmen..

I'd say thats about OH&S and would apply to any vehicle, diesel or petrol.

voltage spikes or load dumps

A risk (remote) if jump starting but where would these come from in a tow/clutch/bump starting?

I have seen at least two vehicles where damage was caused to the tailshaft when trying to clutch start the vehicle....
and I know of one other suspected diff failure that was attributed to the "clutch start".

Well if you're a mechanic then you agree that you would have to be pretty mechanically brutal or reckless for this to happen? I bet you wouldn't damage your vehicle if you had no other choice than to try this?
Not everyone has mechanical empathy.

Mick

[01Rod Junior Member Find all posts View Profile Close 01Rod]

Re: Can you bump start a new Diesel motor?

[quote:2x7nuopl]and I know thats what the auto clubs like RACQ also train there patrolmen..

I'd say thats about OH&S and would apply to any vehicle, diesel or petrol.[/quote:2x7nuopl]

No OH&S say's not to "Push" a vehicle.. but no problem at all to clutch start a petrol vehicle just not Diesel...

[quote:2x7nuopl]voltage spikes or load dumps

A risk (remote) if jump starting but where would these come from in a tow/clutch/bump starting?[/quote:2x7nuopl]

The risk comes from the fact that the car could be started with a battery that is not capable of protecting the vehicle from surges or spikes..
in electronic terms the battery acts as a big capacitor (sponge) that will soak up any stray current.
Lets think of it this way... If the car won't start because the battery has failed, then you clutch it and get the vehicle running, the vehicle is now running with a faulty battery that may not be able to protect the vehicle from a voltage spike. when a surge or spike happens it has to be absorbed somewhere, if the battery can't do it then it will keep going until it finds something that will... most times being some of the electronics.

Alot of people don't understand the relationship of the battery in a modern motor car.. it not only starts the car and provides electricity but it also protects the electronics.

I see electronics damaged due to incorrect jump starting almost everyday in my job...
and see similar damage done by clutch starting the vehicle reasonable often as well..

[quote:2x7nuopl]I have seen at least two vehicles where damage was caused to the tailshaft when trying to clutch start the vehicle....
and I know of one other suspected diff failure that was attributed to the "clutch start".

Well if you're a mechanic then you agree that you would have to be pretty mechanically brutal or reckless for this to happen? I bet you wouldn't damage your vehicle if you had no other choice than to try this?
Not everyone has mechanical empathy.

Mick[/quote:2x7nuopl]
yes i would clutch my car if the circumstances were right..
ie battery just a little down on voltage.. IE door left open for a few hours..
or a faulty start motor... etc..

BUT... I wouldn't even bother if the battery was completely discharged, or I had any doubts about the condition of the battery..

Two examples of where damage occured.
1.Landcruiser Builders ute, rolled down driveway (fairly steep)and clutched in reverse - Tail shaft bent...
2.Nissan Patrol - towed behind another vehicle due to vehicle not starting (glow plugs, they didn't know that at the time) popped clutch, loud bang and rear wheels locked up snapping tow strap.. Broken diff...

[Wil Senior Member Find all posts View Profile Close Wil]

Re: Can you bump start a new Diesel motor?

my 2 cents,

In an older 120 series work pardo pre D4D I left the fride plugged in and it drained the battery completly. We roll started it with no problems.

Will

[MickL Addicted PP Member Find all posts View Profile Close MickL]

Re: Can you bump start a new Diesel motor?

I still fail to see where there is a danger of a "Spike" from push/tow/bump starting. (Different to jump starting where a poor clamp contact or removing leads under load could cause one)

Unless the battery is open circuit then it makes a better capacitor when flat than it does when fully charged.

As for the mechanical damage I struggle to believe (unless the cylinders are full of fuel or coolant) that the engine would provide enough mechanical load to cause this unless there are other factors at play.

The only reference to not doing it I can find are from car manufacturers themselves and the reasons are not mechanical but due to raw fuel possibly damaging the performance catalytic converter or diesel particle filter.


Mick

[Wil Senior Member Find all posts View Profile Close Wil]

Re: Can you bump start a new Diesel motor?

Just for kicks, I just roll started my 08 Rodeo diesel, no issues - note: the battery was at normal servicable level.

Can't test the current prado for you as its auto.

Off topic, but if the starter packs it in, is there any way to start an auto?

Will

[StormyKnight Advanced Member Find all posts View Profile Close StormyKnight]

Re: Can you bump start a new Diesel motor?

Well you wouldn't roll start it in 1st or 2nd gear, thats when you would break something! Perhaps 3rd or 4th, you only need it to idle at the speed you can push it at.....

Off topic, but if the starter packs it in, is there any way to start an auto?

Will

Um No. (Thats the short answer

Fix/replace starter (Thats the not so short, but doable answer)

You could bypass the overdrive clutch in the auto gearbox, somehow get the auto to run in the 1:1 ratio & pull gentle enough not to break anything.....(Thats the "Well I tried everything else" answer)

Cheers

[zookcubr Senior Member Find all posts View Profile Close zookcubr]

Re:

The Q. was "Can you bump start a new Diesel motor?"

Is there anybody out there that did a ADF truck driving course?

F1s and Unimogs (in fact any diesel truck) can start up and drive away without a driver if the vehicle is in gear with the brakes off and has been shunted from behind. Its part of the driver trainer course, and it blew me away. The damm thing took off, and kept going. I say "yes", very much.

[01Rod Junior Member Find all posts View Profile Close 01Rod]

Re: Can you bump start a new Diesel motor?

I still fail to see where there is a danger of a "Spike" from push/tow/bump starting. (Different to jump starting where a poor clamp contact or removing leads under load could cause one)

Just to clarify... the Clutch start will not cause a spike... But if the car gets a spike while it is running as a result of the clutch start and the battery is not capable of absorbing it... then you get damage... remember a spike can be caused by alot of different things.. even a relay closing or opening can cause a small back EMF.. thats why they have changed to transistor relays...

Unless the battery is open circuit then it makes a better capacitor when flat than it does when fully charged.

Not true... A fully discharged battery has a higher internal resistance especially if it has sulphated.. Put an amps clamp on a flat battery start the car and watch the amps will slowly increase as the resistance decreases in the first couple of mins..

As for the mechanical damage I struggle to believe (unless the cylinders are full of fuel or coolant) that the engine would provide enough mechanical load to cause this unless there are other factors at play.

I understand its not something you will come accross everyday... but trust me you can damage a diesel vehicles drive train clutch starting it.... due to the higher compressions in a diesel motor..

The only reference to not doing it I can find are from car manufacturers themselves and the reasons are not mechanical but due to raw fuel possibly damaging the performance catalytic converter or diesel particle filter.

They also tell you a jump start should only be performed by a qualified technician, not how to do it.. or why... none of there technicans even understand how to do this properly to avoid damage...

[Spurio Senior Member Find all posts View Profile Close Spurio]

Re: Can you bump start a new Diesel motor?

What the ???? :shock: :shock:

I get pissed regularly out bush and always manage to leave something on and drain the start battery.

I've roll started at least 6 different D4D M6 more than I can remember and never damaged any electronic or mechanical bits.

Not sure about the voltage spike theory :shock: :shock: but I run extremely sensitive electronic equipment hardwired into the vehicle and never had a problem.

As to the drivetrain damage, basic off-roading opposite lock would produce 3-4 times greater stress than a roll start as drive forces equalize between axles.

As with everything, common sence must prevail, if you tried to roll start at 80km/hr in 1st you are a moron :lol:

[Leethal Advanced Member Find all posts View Profile Close Leethal]

Re: Can you bump start a new Diesel motor?

Interesting discussion so far with some contentious points ...lol

In my experience with modern electronic diesels (of european origin) if you don't have sufficent voltage it will not start .. period!

Most if not all modern electronic diesels (and probably petrols) will have the ECU's protected from low voltage, such that most will shut down even when running when voltage drops below a certain point, look at the threads in this forum about how far one gets with a faulty alternator.

So as to push starting D4D Prado .... if you have flattened your battery below that threshold you can push it all the way home and it won't start.

And if you have a faulty starter but a charged battery .. my thoughts are if the situation demands it ( middle of the Simpson for example) push away with care and most likely you will be ok.

Just my thoughts

Lee

[Eugene Junior Member Find all posts View Profile Close Eugene]

Re: Can you bump start a new Diesel motor?

What the ???? :shock: :shock:

I get pissed regularly out bush and always manage to leave something on and drain the start battery.

I've roll started at least 6 different D4D M6 more than I can remember and never damaged any electronic or mechanical bits.

Not sure about the voltage spike theory :shock: :shock: but I run extremely sensitive electronic equipment hardwired into the vehicle and never had a problem.

As to the drivetrain damage, basic off-roading opposite lock would produce 3-4 times greater stress than a roll start as drive forces equalize between axles.

As with everything, common sence must prevail, if you tried to roll start at 80km/hr in 1st you are a moron :lol:

We regularly bump start, literally, cruiser utes, troopies and 76 wagons and 100series pov packs, both 1HZ and the 4.5 V8, all have flashing lights, big driving lights, work lights and two way etc, they go flat alot when on night work out in the pit, we will use a sling between both, or if both utes, back one up to the other and push away.

the trick is 2nd or 3rd gear, never first, ease the clutch out just like you were moving away fom the lights, key on, generally if there is enough power to turn on the dash lights at all they will start, if not, you have to pull them further to get the alternator creating a charge so it will power the ecu. the old 1HZ start so easy it is almost too easy, walking pace, 2nd gear, easy.