Thread: Measures to combat a runaway diesel engine

Originally Posted by Landy110

Yeah, I've seen it once, in an 80 Series cruiser. The driver dropped the clutch in top gear with the brakes jammed hard on. The vehicle didn't move an inch and the engine revs didn't drop one rev. We ended up cutting the hose that connects to the inlet manifold to stop it.

How can that happen? Was his clutch completely dead?

Originally Posted by Landy110

As a ressult of this the possibility of a turbo fed runnaway has been in the back of my mind. I have another issue though which I have considered may lead to a two birds with one stone solution.

On long steep descents the Deefer tends to run away a bit, once the revs start comming up the turbo tends to push it a bit so I have to ride brakes heavily at times. I was thinking of an exhaust brake, this would prevent the gravity fed runnaway but would it prevent the turbo/oil fed runnaway or would the pressure blow the exhaust.

Alternate option is the throttle body solution pre inlet, would that help with the gravity runnaway though ?

Steve

I have blown turbos before and it didn't cause runaway. It just smoked a lot of blue as at least half that oil will be headed into the exhaust, rather than the intake. While diesel engines can run on liquid oil into the intake, they don't run very well on it, I think you would struggle to drive anywhere on a diesel fuelled that way. Recently due to a provent issue my engine drank about 10 litres of oil via the intake in 1600km. It temporarily ran on it's own oil about 6 times during this dark time.
There is no rush of power and if you combine it with a dead turbo (no boost), you won't be fighting anywhere near the torque of a non turbo diesel to shut it down.

Aside from volatile atmospheres, the biggest cause of runaway seems to be morons cleaning air-filters in petrol or other volatiles, installing them and starting it.
Weeeee. Bang.

If you feel the need to do this, start the engine and then gently install the air-cleaner with it running. You can then easily tell if the engine is going to get high on it.

Originally Posted by Dougal

What has you concerned about engine runaway? It's quite rare. Do you have some extreme modifications or existing problems that increase the chance of it happening?

Originally Posted by tomalophicon

Or am I being overly cautious (i.e paranoid)

Tom.

i vote overly cautious....i have been around diesels both at home and at work all my life, yes i am aware of runaways but have never witnessed one or heard of one actually happening. my bet is whatever you fit will be something you will never use.

Well Ive seen a few ,runaways that is , and everytime they were Detroit Diesel of the 2 stroke variety,and happens just after a sudden shutdown from full load hot condition. In fact the engine actually runs backwards , yes ,so you have to stuff the exhaust with rags to prevent air getting in .All tangentially ported 2 strokes are capable of this !

It certainly does happen, we just don't hear about it much.

Just last month, on the Ring Road in Melbourne. A 3-5 tonne rental truck (Hertz or Budget) was dieseling itself to death, blocking a lane. The smoke was unbelievable.
This truck looked fairly new and in good condition, so the point is that run-away is a danger in a diesel, and an uncontrolled run-away is even more possible with an auto transmission.

This guy in the truck standning on the edge of the road may not have known how or tried to stall the engine ... he must have been saying 'how much excess is the rental company going to slug me ....'

I will concur that this is still a rare event, we probably have more luck in winning the lotto. However, its not just sump oil that can cause it. When injectors leak (think TD5's), there is a nice concoction of diesel and fuel in the sump that can get going as well.

Dougal, the clutch would not have been in new condition but he did drive on it for ages after he had the engine repaired.
The problem is that the engine is revving so fast that the clutch just can't grab !

The engine isn't running on liquid oil when this happens, the turbo is hot and spinning fast so the oil is vapourised and mixed very efficiently with air and pumped straight into the cylinder. Believe me, it is an excellent fuel-air mixing event as the Land Cruiser diesel would never reach 10,000 rpm plus with it's normal fuel system. I am guessing at the 10k rpm, it sounds more like 40k in the circumstances but that is just adrenalin.

There was a plume of smoke issuing from the exhaust that was reminiscent of rocket engine tests in the 60's. It was litterally comming out so fast it looked like a rocket. My defender was parked about 20 mtrs behind the cruiser and it disappeared in smoke within about 6 seconds.

Apparently bits of turbo were removed from the inlet manifold but none went into the engine, very lucky, but I bet the old girl never felt or sounded quite the same.

Originally Posted by Landy110

Dougal, the clutch would not have been in new condition but he did drive on it for ages after he had the engine repaired.
The problem is that the engine is revving so fast that the clutch just can't grab !

I've never heard of that before. Clutches have no problem working at the rpm's that that sport bikes run at.

Originally Posted by Landy110

The engine isn't running on liquid oil when this happens, the turbo is hot and spinning fast so the oil is vapourised and mixed very efficiently with air and pumped straight into the cylinder. Believe me, it is an excellent fuel-air mixing event as the Land Cruiser diesel would never reach 10,000 rpm plus with it's normal fuel system. I am guessing at the 10k rpm, it sounds more like 40k in the circumstances but that is just adrenalin.

Turbos don't vapourise oil, they centrifuge it out against the scroll housing and throw it out as liquid which runs along the intake piping. As I said earlier, I have had one of my diesels do this.

The burn speed of liquid oil isn't fast enough to get 10,000rpm, especially with the pre-ignition of uncontrolled injection. 2500-3000rpm was where my engine would sit and sound bloody awful doing it.

But being a cast steel Isuzu, my engine survives such torture.

surely this thread is a joke, I mean look at the date it was started......and while there are many wives tales of this mythical run away, how is it ever possible for a good, healthy perfectly sound engine to run away.....I mean, come on!

Yea, I'm with Uninformed, must be a bit of a gee up hey :-)....... one solution.... V8