Runaway Diesels

Siia109

Well-known member
So I'm falling down the youtube rabbit hole with diesel repair videos and the 200TDI / 300TDi videos as I am learning my way - and up pops a D90 with a "runaway diesel" - smoking and high RPM until failure as people dove for cover.


I knew about "dieseling" even petrol engines do that - but never heard of the runaway diesel. Further reading it is something that is rare, older engines are more prone to it as the newer engines have more control over the fuel, and it happens mostly to turbos.

Some how "additional fuel" gets sucked into the engine causing the engine to just redline. One write up referance the oil in the turbo if it gets sucked in this will cause the engine to run wild. Still not clear on where that much additional fuel could come from - didn't think oil would contribute to the engine red lining.

My question to the group - How common is this? how would this happen on a 200 or 300 TDi? and has anyone seen it happen and can it happen while your driving down the road? - because its scary AF when these engines just take off and unless you suffocate them from intaking air there is nothing to do but run!

Thanks
 

chris snell

Administrator
Callsign: NW5W
Staff member
As I understand it, it's a turbo failure that leads to oil going in along with the intake air, which causes the engine to speed up, which spins the turbo faster, which feeds more oil in and so on.

I've heard various ideas to stop it. Throw something over a raised air intake. A butterfly valve on the air intake.

Personally, this feels like something that happens to people that don't do a good job at preventative maintenance, who don't have EGT gauges, and who don't inspect their engine bays regularly for new leaks.
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
The diesel can easily run on engine oil - so if there is a big oil leak into the air intake, the engine may run even if the fuel pump is shut off.
It happens more frequently in turbodiesels - the bearing in the turbo can fail catastrophically, and if it is force-lubricated by engine oil, this oil will go into the cylinders. The faster the engine spins, the more oil is thrown into the intake, causing it to "run away."
The only way to stop it is to shut off the air intake, just as Chris had said.
 

erover82

Well-known member
Runaway can also happen when too much oil passes through the crank case ventilation system and back into the intake. By design, engines burn whatever comes through the PCV system, which is normally just hydrocarbon gasses as any oil is returned to the sump by the PCV oil separator. However, a failing or overwhelmed separator leads to that oil being sent through the intake. In extreme cases this can cause a runaway scenario. IIRC this was actually a potential issue on 2.5NA and 2.5TDs which prompted LR to revise their PCV systems.
 

MountainD

Technical Excellence Contributor
best thing you can do is starve it for air as quickly as possible. I don't care if it is a piece of cardboard over a side vent, bag on a snorkel or whatever you can find over where ever it is pulling air. Crush the air intake if you have to. You can't control any other variable.
 

evilfij

Well-known member
Maybe I am a redneck, but everyone I knew with an old diesel they were messing around with kept an appropriately sized piece of wood around to block the intake. Like a piece of 2x8 (also helpful as a Jack base). You need something strong as something like a rag will likely just be sucked into the intake. Cardboard over the side intake might work, but I suspect it might not if it’s really in runaway. Heck, it could suck the intake hose. Anyway, do what you can with what you have and do it quickly.

I did hear a story of a runaway rover Tdi from a tech who worked in Europe, but that one another tech filled the engine oil without draining the engine oil.
 
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hillstrubl

Founding Member
I'd by lying if I didn't have a big piece of rubber to hold over the side air intake within an arms reach just in case.
 

evilfij

Well-known member
So the detroit is not a true runaway where it’s eating it’s own oil. Detroits the rails stick.
 

jymmiejamz

Founding Member
Callsign: KN4JHI
I’ve seen it a bunch of times at the dealership. Every time has been when a TDV6 has been overfilled with oil (usually not enough drained during oil change). The oil somehow ends up pooling in an intake hose. At idle and light throttle there’s no issue, but as soon as you put your foot in it the oil gets sucked back into the intake and it runs away.

Worth noting that these motors have an electric throttle body to aid in quick engine shut down which will not stop it once it runs away. It’s pretty spectacular to watch one blow up and throw rods through the aluminum skid plate.
 

vtlandrover

Well-known member
I once had a diesel run away from me. The responding LEO told me I was crazy when I asked if he would block my Rover before it ran someone over; the firemen thought I was crazy when I asked for "TWO!" chalkblocks, please, "'cause one ain't gonna stop it!"
 

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vtlandrover

Well-known member
A just-installed, rebuilt GM alternator internally fried and backfed the starter... luckily I had it in 1st and not reverse.
 

vtlandrover

Well-known member
They wouldn't let me near it. I had fire extinguisher in hand and was told to step back. Not wanting an arrest on top of a totalled Land Rover, I cut my losses and backed away.
 

Siia109

Well-known member
So the the starter push the engine to run away?

If only there was a conversion available to a simple petrol...anyone....;)
 
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