Diesel runaway - stopped miraculously by itself

Question

A little background (Little longer, please excuse):

Few days before while we were driving Maruti Suzuki Dzire vdi (Engine: Fiat Multijet 1.3 DDIS, CRDI engine) around 40kmph. All of sudden there was a noise from engine and while we attempted to pull over to the side, the engine started to run away. We parked the car on the road side and removed the key but still the engine was running at its peak RPM with plumes of white/grey smoke covering the entire road. At the time of this happening it was our first experience and I was not aware of diesel runaway. We opened the bonnet (engine hood) and was literally frozen due to panic.

I thought the throttle pedal has stuck and hence tried to tap it with my hand and magically engine died. I do not know how it stopped. The coolant boiled over the expansion tank and the engine was hot and smelly and with huge crowd gathered around pouring in advice. We could not think anything wise. I reinserted the key and switched on the ignition (engine not started) thinking the radiator fan could run.

The car was towed away to an authorized service center and they were puzzled about this. Apparently none there were aware of diesel runaway. First they reported that the high pressure diesel pump had failed and was just hanging on to the engine on loose fasteners. Then they said the pump did not fail. They cleaned EGR valve, intercooler. Intercooler was flooded with engine oil, engine oil topped up and started white smoke spewed out for few minutes and then became normal.

Meanwhile I read about diesel runaway (see this video of a similar incident in YouTube) and understood that in my case the engine oil was acting as a fuel. The only way it could go in was through breather pipe or turbo charger seal failure or extremely worn out piston rings. With the noise heard just seconds before runaway and with the observation of having engine oil inside inter cooler I quickly came to conclusion that turbocharger should be the source of problem.

After few days the service center staff performed a compression test and said 2 cylinders achieve compression ratio of 18:1 and other two achieved only 12:1. The white smoke is gone but still could see some trail of smoke (seems normal for a diesel engine). I thought I should have written off the engine, but to my surprise they charged me half of what they charge during normal service. They charged for EGR and intercooler cleaning and oil topup. While driving now there is a significant power loss.

My questions:

1. How did the engine runaway would have stopped? If it had stopped by consuming the engine oil significant damages should have occurred. But this was not the case reported by service centre staff. I have not blocked the air intake and the smoke was only spewing at the rear of the car and front (engine bay) remained clear.
2. What would have caused the runaway? If it is the turbo seals, then the car should have trouble using afterwards.
3. The loss of compression is not analysed further as we do not want to open up the engine causing high cost. Leak down test could have been done to identify whether the poor compression was due to valve or piston rings. Service center staff were not aware of this test and so do I until after reading further. What could have caused the loss of compression?

Answer 1

I'm not familiar with your engine, but on the VW TDI engines quite a bit of oil can accumulate in the intake, particularly in the intercooler. The last time I did the timing belt I found about 100 CC of oil in the intercooler. I'd never though to clean it out before so I don't know how long the oil had been accumulating. I also don't know what circumstances would cause the engine to start picking up the oil, but I've seen claims that the VW engines can run away on that oil source.

If something like that happened on your engine, exhausting the supply of oil in the intercooler could explain why the run away stopped. In the VW engines there is an "anti-shudder" valve that is, in normal circumstances at least, capable of shutting down the engine (from idle). It sits in the EGR valve and acts a bit like the throttle plate on a gasoline engine, but it only has two positions fully open and fully closed. I think the intent of the valve is that it would also serve to shut down a runaway engine, or at least limit air enough to provide some control.

Answer 2

Regarding loss of compression

The loss of compression can be explained by the evidence of oil in the cooling system.

The usual way the two fluids mix is when there is head gasket failure and/or warpage of the cylinder head.

In the case of cylinder head warpage, the head does not seal some of the combustion chambers completely, which results in low compression figures since gases then have an avenue to escape through.

Answer 3

I have owned many VW diesel cars since 1977.

Runaway in the IDI engines was more common than in the TDI engines.

In general, runaway is from the ingestion of oil, normally pooled in the intake manifold (IDI) or somewhere in the intake system like the intercooler on TDIs. This is for VW, and I am sorry, I cannot address your specific car.

When runaway happens, there is usually a sipping of oil from the manifold, and the engine increases power output. The increased flow then sips more oil, which may have already collected in an area.

One way this can happen is after a long period of operation (not necessarily one drive) the oil pools, and then there is an instance that you "step on it" and increase flow. This pulls a slug of oil from the intercooler area up to the intake area where it is ingested along with air, and burns in the engine. For example on a 48 hp VW IDI engine, like used in 1978, it can produce well over 80 hp. The oil is not atomized, and will burn smokey, and stinky. The engine may overheat. It may over RPM and grenade parts.

So on a diesel with a manual transmission, your best technique is to KEEP THE CAR IN GEAR, do not release the clutch, and brake as hard as practical to slow the engine, and stall it out.

Others are correct in saying that as a part of maintenance, one should be checking for oil in the intercooler, or anywhere there is a low spot where crankcase blowby or turbo oil leakage can accumulate.

Crankcase blowby may be higher in a diesel engine than a gasoline, and if it is high, it will blow a mist out of the engine (usually via a crankcase ventilation valve). Some engines have a collection area, where the mist can collect, and the liquid oil is returned to crankcase service or disposed of. Most do not.

In your specific instance, you do not give us information on the age of your engine and it's service history. Is it a high time engine? If so blowby may have contributed to this problem

Also, if a large slug of oil was ingested it is possible, and I have seen it in VW IDI engines, that the rings will crack (and/or connecting rods bend) due to large amounts of oil being inducted into the cylinder and not able to compress (also called hydro lock). This type of damage is expensive to repair, and requires a lower rebuild on the engine.

Even if the above happened, and you can find your source of oil and reduce the accumulation or flow, you might still get some more service from your engine, but with lower efficiency.

Finally, as a general point for diesel users, some suggest that sometimes demanding high power from your engine, frequently (let's say every 100 miles or so-but I don't have a firm recommendation), will keep large amounts of oil from collecting in the intake, and ultimately causing a larger ingestion of oil.

To close, what I have done on the four TDI ALH engines, is to install a drain hole with a screw and o-ring on the bottom of the intercooler. At oil change, I drain the intercooler. Usually there is little there, but if the amount were to increase, I would try to determine the reason, and reduce the accumulation.

You may wish to look for a forum which addresses your car, and see how others might deal with engine oil fueled runaway risks. Good luck.

Answer 4

runaway can damage valves, bend connecting rods and overdrive fuel pump, take out injectors or glow plugs and measure each piston height,"don't drop your masure stick down the hole" check tappet gaps to big or small will help check valve damage, and weaken fuel pump on older engines with mechanical belt driven system, check blocked oil return from turbo as this can block and bust seals, got one at the moment, with probably all above, good luck.

Diesel white blue smoke stinky fuel smell is unburnt fuel (will burn your eyes) Air filter check, pump low pressure not squirting fuel correct, with misfire, or lack of power, low compression not firing right, vales or rods, or hope injectors, belt jumped a tooth rare, blocked fuel filter maybe, remote from a clean bucket of fuel to pump maybe with injector cleaner or sun flower cooking oil mixed in (great injection cleaner), no changes, after check filter for metal shiny bits that have returned , pump drain it and check for bits. Compression - fuel supply - Air. on electric injectors check with dia reader and any of above, good luck hope it helps.