Diesel runaway - do you have action plan / take precautions?
 

As far as I can see following a brief search here, this is a very rarely mentioned subject on this forum.

And I hate to spoil any diesel driver's day if they don't know what diesel runaway is.
Keep in mind though, such events are relatively rare, so don't panic.

I haven't had runaway but I know someone who has ( my nephew, it killed his engine ) - in an old Audi 2.5 litre AEL engine quite a few years ago.

And yes, that is, to all intents and purposes, the same engine as in an 850, S/V70 2.5D TDI like mine.

The Volvo D5252T.

But, runaway is not a phenomenon exclusive just to the AEL engine, it is a potential problem for many high mileage diesel engines.

I don't profess to have great knowledge of runaway but I do know that once it starts it can be very difficult to stop and often ends in destruction of the engine.

Runaway is caused by the engine having an alternate supply of fuel other than that contained in the diesel tank.
Diesel engines will run on sump oil.

That alternate supply is usually the sump oil leaking through various routes, and because it is not ( metered and ) passing through the diesel pump, turning off the ignition ( and thus closing the electromagnetic pump fuel cut off valve on a TDI ) has no effect - the engine keeps on running with no restriction provided by pump metering and, with ever increasing RPM until the sump oil is exhausted or other failure.

PUTTING IT SIMPLY - TURNING OFF THE IGNITION DOES NOT STOP THE ENGINE.

My nephew who had the failure on his old Audi now drives a ( ~1998 ) V70 TDI, but as a precaution, he also carries a CO2 extinguisher to inject into the air inlet should the same incident happen to him.

It is believed that his runaway was caused by (a) failed turbo oil seal(s) allowing engine oil into the inlet manifold thus fueling the engine.
His car was a manual and it caught him by surprise and with little previous knowledge of runaway.

I'd be interested to know if YOU have taken specific precautions or have a fast action plan should a similar event occur to you.

There would be no time to waste.

What about an auto like mine where you are unable to quickly stall the engine by letting the clutch up in gear with brakes applied?


Take a look at some YOUTUBE diesel runaways but don't fret - and lets see if some sort of standard urgent action plan can be drawn up without renewing every single thing on an old ( or high mileage ) engine that could cause a runaway.

I hope to keep my TDI a good few years yet.

What about D5's too?

Please discuss!!

Colin

If you like the car then best have a plan, if not do as most do and film it then stick it on youtube when it blows. Usually a rod pops out the block.

Manual stick it in top and stall it.

Auto the only way you can do it is starve it of air. If you have an induction kit (yes I know on a diesel, how vulgar) smother it with a jacket or something.

On some like the audi engine iirc the pipe from the maf to the turbo is rubber so squash that flat to starve it.

However when a runaway happens that last thing you want to do is stop safely, casually pop the bonnet and deal with it if you can't stall it.

Your instinct is to leg it. Especially if its a big engine like on a dozer etc, they go bang in a big way lol

It's very, very rare for an oil seal in an OEM standard diesel turbo to fail in such a way as to allow a significant inflow of engine oil. Unfortunately it's a different story if a turbo has been rebuilt with a cheap oil seal.
Obviously driving around with a defective turbo and one that is starting to emit oily white smoke in particular is risky in terms of a potential runaway.

If you do get a runaway on an auto that can't be stalled, I would not play around lifting the bonnet up, because the cooling system overheats and that can cause a sudden steam explosion from the header tank or burst pipe.

Have a multi tool in the car, you can then undo the jubilee clamps on the intake hoses and shove something in there to block the airflow, starving the engine of oxygen and it should stall.

The question for me though is how much, if any damage had already been caused to the engine by the time you stopped it. Is a complete strip down and rebuild better or cheaper than just sourcing another engine.

It's so rare it's not worth worrying about IMO, and I'm not sure I'd want to get too close to a runaway engine anyway as occasionally they fail spectacularly.

That said if you carry a CO2 extinguisher in the boot emptying it into the air inlet should do the job.

My procaution is to keep my oil level at 3/4 full as volvo advise. To allow for the possible diesel contination and rise in oil level. It's never risen but if it does at least I have some breathing space.

you can get a runaway due to over filling the oil level.

I've read thousands of threads on here and haven't come across runaway once.
That tells me to give it the same priority for having an action plan as alien invasion or the second coming.

Thanks for all the replies.

I don't have an obsessive worry about this happening to my car, especially following replies here.

I believe the turbo on mine is the original as service receipts don't show a repair or replacement being fitted, and I don't have excessive smoke from the exhaust either.

I'll be sure not to overfill the engine oil too.

Just to be safe though I think I will begin to carry a small CO2 extinguisher in place of the car extinguisher I usually carry.

I think my nephews experience had played on my mind a little.

Colin

I thought all modern diesels have a throttle body which is effectively an air cut off valve.