[Vwdiesel] Runaway Rabbits ---( and Jettas 1977 to 1984 )

[Val Christian]

Typically, the crankcase oil pools in the intake manifold, and is 
ingested when it gets to a high enough level, or the vehicle
has acceleration forces shich shift the pool of oil to a "drain hole"
in the casting.

Popping the airfilter, and looking for signs of pooled oil in the
intake is a good diagnostic method of identifying the primary cause 
of runaway.  Additionally, blotting up excess crankcase oil in the 
intake manifold may defer occurrances of runaway.

High RPMs are an aggrivating factor, because there is more atomization 
of crankcase oil, combined with slightly more blowby, creating a flux
through the crankcase.  High torque tends to increase blowby.  All
of this is somewhat academic, because the runaway occurs when the 
oil gets ingested, which is not necessarily when most of it is transported
to the intake manifold.

In diesel VWs, the mix of fuel with crankcase oil is normally of little 
consequence, with respect to runaway.  In some larger diesel powerplants,
the dilution of crankcase oil with fuel has been documented as a
contributary factor in runaway.

Furthermore, the most significant path of fuel dilution of crankcase 
oil in VW diesels, is poor compression.  Not because of blowby, but 
rather due to long cranking periods in extreme cold weather.  The
uncombusted fuel works it's way past rings readily.  Once the engine
is running, most of the fuel oil is combusted, unlike what can happen,
especially in large bore gasoline engines idling cold.

Finally, while I've never used one, others have described collection bottles
for crankcase oil venting.  There are commercial versions of this for 
aircraft engines.  Essentially, they create a separator, and the collected
crankcase oil is sumped and typically reintroduced into the crankcase.

Val

> 
> I have been under the impression that runaway was caused by the engine 
> burning the LUBE OIL as fuel.  I did not think that it was caused by the lube oil 
> being diluted with DIESEL.  It therefore would not have anything to do with cold 
> idling, but rather high rpm, lots of blowby, and potentially problems with 
> crankcase vent.
> Andrew 
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