Cable Forum - View Single Post - Runaway bus accelerates 'like a bullet' on London's streets and smashes into car

rhyds · 17-04-2015, 12:48

Diesel engines are known to sometimes "run away". What happens is that either the engine becomes badly worn, or that an oil seal fails in the turbocharger, and the engine then starts to suck in and run on its own engine oil.

Now, Diesels (unlike petrols) control engine power (the "throttle") by controlling the amount of fuel that's being injected in to the engine, rather than controlling the amount of air as with petrol engines. What happens when an engine runs away is that because the engine is sucking in hot (and therefore thin) engine oil (which is basically what diesel is) it starts accelerating, causing more oil to be sucked in, and the cycle continues.

Simply turning the ignition key or battery isolator off will not do anything, as this simply cuts off the flow of diesel, but as the engine is burning its own oil this does nothing. The only ways of stopping it are to try and stall it (risky as the engine is basically at full power, and impossible with an automatic), strangle its air supply (either by blocking the air intake or dumping something like CO2 from a fire extinguisher in to it) or simply selecting neutral and letting the engine blow itself to pieces.

I'm not sure if this type of bus engine is susceptible to this kind of failure, but I know many Turbo Diesel cars (mainly 1.9 Renault diesels) that have failed in the same way.

17-04-2015, 12:48	#8
rhyds Inactive Join Date: Mar 2014 Location: North Wales Services: Plusnet Phone/BB, Freesat, VM Business BB (Cable) Posts: 821	Re: Runaway bus accelerates 'like a bullet' on London's streets and smashes into car Diesel engines are known to sometimes "run away". What happens is that either the engine becomes badly worn, or that an oil seal fails in the turbocharger, and the engine then starts to suck in and run on its own engine oil. Now, Diesels (unlike petrols) control engine power (the "throttle") by controlling the amount of fuel that's being injected in to the engine, rather than controlling the amount of air as with petrol engines. What happens when an engine runs away is that because the engine is sucking in hot (and therefore thin) engine oil (which is basically what diesel is) it starts accelerating, causing more oil to be sucked in, and the cycle continues. Simply turning the ignition key or battery isolator off will not do anything, as this simply cuts off the flow of diesel, but as the engine is burning its own oil this does nothing. The only ways of stopping it are to try and stall it (risky as the engine is basically at full power, and impossible with an automatic), strangle its air supply (either by blocking the air intake or dumping something like CO2 from a fire extinguisher in to it) or simply selecting neutral and letting the engine blow itself to pieces. I'm not sure if this type of bus engine is susceptible to this kind of failure, but I know many Turbo Diesel cars (mainly 1.9 Renault diesels) that have failed in the same way.