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Old 20th December 2018, 19:45   #1
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Default Diesel Engine Runaway - What it is, and how to stop it

Here's a quick, not very detailed, crude thread on Diesel Engine Runaway - What it is, and how to stop it. Mainly as a precaution thread. (Note, I'll be posting only on one case which I feel is most relevant in our conditions, ie. due to blown turbo oil seals)

So, what is diesel engine runaway?

Watch the video:

As you can see in the video, during a diesel engine runaway, an engine revvs uncontrollably, spewing out thick smoke, and even if you try switching off the engine by turning the key OFF or switching off the fuel supply, it continues to revv madly till the engine dies., In most cases there will be nothing to salvage from the engine if it dies like this. This can happen to anyone who has a badly maintained (turbo) diesel engine.

So, what causes an Engine Runaway?

A diesel engine doesn't really require diesel to run. All it needs is combustible oil in the combustion chamber at the right temperature and pressure. So, whatever the reason through which oil reaches the combustion chamber, and is not meant be, the engine will start running away! There are few causes for engine runaway, but here I'd like to discuss on what I feel the most relevant cause for a small/medium sized passenger car turbo diesel engine is. Due to a blown turbo oil seal.

Diesel Engine Runaway - What it is, and how to stop it-turbolader_separator_en_separator.jpg

We all know that most of the Turbos are lubricated by oil. With improper turbo maintenance, most times, the first thing to go wrong on a turbo is the oil seal. As you can see in the picture, the oil seal is in between the exhaust side and the intake side of the turbo. Once the oil seal is blown, the turbo can spew oil into either compartment. If its the exhaust side, it's comparatively safer, but, if its the intake side, most times it just gets burnt, but, if it spews oil to an extent that the engine no longer requires fuel and uses the oil to combust, the runaway starts.

The engine uses the oil as fuel and starts revving. In a diesel engine, the more the fuel, the more the rpm. The more the rpm, the more the suction at the intake, the more the suction, the more oil is spewed into the combustion chamber, and it becomes a self-feeding destructive mechanism. And the engine runs at very high rpms burning all the engine oil, and this continues till all the oil is burnt off. By the time, the oil is burnt of, the engine is overheated, deprived of oil & has run in extreme conditions. All of which mostly means is a permanent irreparable death to the engine.

What to do in an Engine Runaway situation.

A diesel engine runaway is extremely dangerous. Once the engine starts revving uncontrollably, we all instinctively turn off the key or pull the stop lever. This WILL NOT STOP the engine since diesel is no longer used as a fuel. Moreover, the vehicle might start accelerating itself. One thing I would like to highlight is that, if you are ever in this situation, the priority should be saving yourself, then save the vehicle. Since the engine has started running at high rpm's, you need to first get the vehicle in control. The best way is to try and use the BRAKES ONLY to slow down the vehicle, NO CLUTCH. Possibly steer the vehicle to safety and meanwhile let the engine shut itself off.. Or:

- To stop a manual geared runaway car, my first suggestion would be to stay in whatever gear you are DO NOT PRESS THE CLUTCH, engage the hand brakes, press the brakes HARD. If your friction plate and gearbox is in good condition, the engine should shut off without any drama. If this doesn't work, try slotting into the highest gear and engage the handbrake, and press the brakes and dump the clutch. Pressing the clutch to change to the highest gear will make the engine free up and it might go revv higher than the redline and you might not get a chance to put it in gear again. So you have to be quick on your gear change.
- If its an automatic car, or if you have a CO2 fire extinguisher handy, you can locate the intake and flood the intake with the fire extinguisher. This will choke the engine of air.
- The third and most tricky, dangerous, but, successful solution is to block the air intake. This is IF you have lost all use of your drivetrain. However, in most cars, finding the intake is a pain. Also, the plumbing, if made of plastic or flexible material, will just pinch making it difficult to hold the air. However, if you are sure to find a solid piece of your intake plumbing, then just choke it and the engine will starve itself of air. Assuming your plumbing doesn't have leaks.

IF you are lucky enough to have stopped your engine in time, then in no case should you try and start it again. The process WILL repeat itself. Call your service centre, or a reliable mechanic and get the car towed/flatbeded to their workshop.

--------------------------------------------

An Engine Runaway situation will be pretty embarrassing and overwhelming with all the smoke, sound and heat. I hope with properly maintained vehicles, this situation never happens to any of us. But, if it does, I hope this post will help.
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Old 20th December 2018, 20:51   #2
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Used to be not-so-uncommon in the Ambassador 1.5L diesel engines, even without a turbocharger. Related to piston blowby > crankcase vapour recovery circuit, AFAIR. The way to stop it was to yank on the decompression switch and hang on for a minute or two.
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Old 20th December 2018, 21:43   #3
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Isn't this a problem only for old non electronic engines?
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Old 20th December 2018, 21:54   #4
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Quote:
Originally Posted by Kosfactor View Post
Isn't this a problem only for old non electronic engines?
Yup, modern machines have an electronic cut-off valve that chokes the intake when the ignition is turned off.
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Old 21st December 2018, 08:42   #5
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

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Originally Posted by ashwinprakas View Post
Yup, modern machines have an electronic cut-off valve that chokes the intake when the ignition is turned off.
This is the first time I'm hearing about this. Are the Fiat MJDs and Hyundai CRDis equipped with this?
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Old 21st December 2018, 08:58   #6
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Good information Dhanush.

I guess the runaway condition is very less likely in modern electronically controlled diesel engines? I have not heard of any runaway of a diesel engine till now with the modern diesels.
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Old 21st December 2018, 09:05   #7
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Quote:
Originally Posted by Kosfactor View Post
Isn't this a problem only for old non electronic engines?
Quote:
Originally Posted by ashwinprakas View Post
Yup, modern machines have an electronic cut-off valve that chokes the intake when the ignition is turned off.
Quote:
Originally Posted by --gKrish-- View Post
This is the first time I'm hearing about this. Are the Fiat MJDs and Hyundai CRDis equipped with this?
Diesel Engine Throttle Body (Explained: Why Diesel engines need a throttle body & throttle plate)

Diesel throttle body is not a guaranteed method in preventing diesel engine runaways. It is included in the modern Diesel engines for other reasons. Though it will help turn the engine off by other means (as mentioned in post 1) if not by itself provided IF the valve can close itself AFTER the engine is shut down electrically, which means key turned off.

Most of the modern diesels have it. 1.3MJD doesn't have it 1.6MJD has it. Hyundai's current line up probably has it.

Do not overfill engine oil in diesel engines, do not over fill oil in any engine, but Diesels love to feast on oil given the chance

Last edited by Sankar : 21st December 2018 at 09:10.
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Old 21st December 2018, 10:19   #8
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Quote:
Originally Posted by SS-Traveller View Post
Used to be not-so-uncommon in the Ambassador 1.5L diesel engines, even without a turbocharger. Related to piston blowby > crankcase vapour recovery circuit, AFAIR. The way to stop it was to yank on the decompression switch and hang on for a minute or two.
Yes, that and through the rings used to be the most common reason back then, I guess. Now, the need of this specific thread is because I've been hearing about a few old gen Scorpio's running away! Turbo failure.

Also, the K03 (dont remember the model number) turbo used in the Scorpio and I guess the Thar if pushed hard, in the long run, might behave in the same manner.

-----------------------------------------

Also, one more situation where this will happen is when your car topples over and you try to start it after getting it on its feet. While this is rare in everyday scenario, its common in motorsports.

The oil will have flooded the intake manifold when the was car was turtle, and when you put it back and start the oil in the intake manifold will cause the engine to revv uncontrollably. However, this will last only till the oil in the plumbing is used up. But, will cause damage neverthless.
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Old 21st December 2018, 10:40   #9
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

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Originally Posted by Sankar View Post

Diesel throttle body is not a guaranteed method in preventing diesel engine runaways. It is included in the modern Diesel engines for other reasons. Though it will help turn the engine off by other means (as mentioned in post 1) if not by itself provided IF the valve can close itself AFTER the engine is shut down electrically, which means key turned off.
One would imagine that on a modern ecm equipped engine, unless the ecu asks injectors to pump for fuel, it isn't going to run any faster on it's own. However, the oil carried into the cylinder through a leaky turbo or the PCV system then can speed up the engine rendering all electronics useless.

There could be many reasons for this to happen, but not knowing how many modern diesel engines have a built in failsafe is worrying.
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Old 21st December 2018, 10:53   #10
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Quote:
Originally Posted by Kosfactor View Post
One would imagine that on a modern ecm equipped engine, unless the ecu asks injectors to pump for fuel, it isn't going to run any faster on it's own. However, the oil carried into the cylinder through a leaky turbo or the PCV system then can speed up the engine rendering all electronics useless.

There could be many reasons for this to happen, but not knowing how many modern diesel engines have a built in failsafe is worrying.
There is no cause for worry. The entire country runs on Diesel and how many cases do we know of anyone getting injured in a Diesel runaway.

The intention of this thread is to create awareness. Just be prepared with the knowledge of what could happen in the worst case and have an idea on what to do if it happens (it will almost never ever happen in a properly maintained vehicle).

Again, do not overfill the Diesel engine.

Last edited by Sankar : 21st December 2018 at 10:54.
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Old 21st December 2018, 11:14   #11
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

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Originally Posted by --gKrish-- View Post
This is the first time I'm hearing about this. Are the Fiat MJDs and Hyundai CRDis equipped with this?
I have seen a Swift Diesel suffer a "Diesel Runaway". The engine ran for some time belching out smoke heavily and then complete silence.
Though modern engines have a host of gadgetry to monitor engine performance, it's always a good practice to follow the scheduled maintenance rigorously which includes timely oil change (the most important) and filling only the right quantity. When I had a Swift Diesel, I had to always fight and stand my ground during oil change as the service center used to fill in 3.5 L (3.1L was recommended).
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Old 21st December 2018, 11:15   #12
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Very informative. Thanks.

Please also elaborate what is the regular maintenance required to avoid having this problem. I don't think there is any work done on the turbo during regular service in routine. This is with reference to verna/vento diesels.
Is there any symptom we should be aware of to detect the problem of seal leak before it progresses to such an extent to cause run-away?

regards.
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Old 21st December 2018, 11:18   #13
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

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Originally Posted by risham View Post
Very informative. Thanks.

Please also elaborate what is the regular maintenance required to avoid having this problem. I don't think there is any work done on the turbo during regular service in routine. This is with reference to verna/vento diesels.
Is there any symptom we should be aware of to detect the problem of seal leak before it progresses to such an extent to cause run-away?

regards.
Some of which I can say-
1- Look out for "sweating", traces of oil in the plumbing, Inlet and outlet.
2- Keep an eye on the oil levels, if within limits no problem
3- Adhere to recommended oil change Intervals
4- Always use the recommended oil grade
5- Do not overfill
6- Make sure to Idle the engine for a min or so before shutting down
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Old 21st December 2018, 11:30   #14
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

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Originally Posted by rakesh_r View Post
Some of which I can say-
1- Look out for "sweating", traces of oil in the plumbing, Inlet and outlet.
2- Keep an eye on the oil levels, if within limits no problem
3- Adhere to recommended oil change Intervals
4- Always use the recommended oil grade
5- Do not overfill
6- Make sure to Idle the engine for a min or so before shutting down
Hi,
Thanks for your response. So what I gather is that general precautions are all. Also Vento does use up some engine oil regularly but I understand its normal for VW.
Point no 6 regarding idling before turning off is I think contentious and subject of many debates even at team-bhp. Is it now settled? Because to implement it is practically difficult. Imagine waiting for one minute everywhere you go!!
regards
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Old 21st December 2018, 12:10   #15
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Default Re: Diesel Engine Runaway - What it is, and how to stop it

Before an engine runaway can happen there will be a few signs indicating a failure with the components.

As the lube oil is burning in the engine, high lube oil consumption with a bluish smoke are the warning signs that the lube oil is finding its way into the combustion chamber/exhaust passage.

On a turbocharger, the turbine side seal is the one which will fail first (due higher temperatures), causing a failure of the seal on the compressor side and finally the oil finding its way into the engine from the air side. Before that, there will be signs like :

1. Bluish smoke, due to lube oil burning in the exhaust pipe because of the failed seal on the turbine side.

2. Noisy operation of the turbocharger.

3. Sluggish response from the throttle.

4. Increase in fuel consumption

Other reason for the oil finding its way to the combustion chamber will be failed piston rings, resulting in:

1. Bluish smoke, due to lube oil burning.

2. Noisy operation of the engine.

3. Sluggish response from the throttle.

4. Increase in fuel consumption.

Monitoring the engine smoke and oil consumption is very important for preventing such type of failures. The tell tale signs to notice are:

1. A white smoke indicates either high moisture content in the air, water in the combustion chamber or lesser fuel available for combustion.

2. A black smoke indicates lack of air.

3. Bluish smoke is indicative of lube oil finding its way either to the exhaust pipe or to the engine.



Quote:
In most cases there will be nothing to salvage from the engine if it dies like this
It is due to the engine over-speeding, and the mechanical components exceeding their stress limits.

Quote:
The best way is to try and use the BRAKES ONLY to slow down the vehicle, NO CLUTCH.
Pressing the clutch will remove the load from the engine resulting in increase in rpm, in worst case the engine components may fail and fly off.

Quote:
IF you are lucky enough to have stopped your engine in time, then in no case should you try and start it again. The process WILL repeat itself. Call your service centre, or a reliable mechanic and get the car towed/flatbeded to their workshop.
The engine will not start even if you try starting an engine which has been into a runaway situation for some time, though its advisable not to attempt as that my save a few components from further failure.

Regards
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