Catalytic Converter Meltdown

["Steve D'Gerolamo" <steved3@xxxxxxx>]

I've had 2 calls in the past 24 hours and know of a few other situations
where a BMW catalytic converter has overheated to the point of ceramic
meltdown or starting a fire.  There is nothing in a catalytic converter
that is combustible....construction is ceramic and stainless steel.  What
causes the excessive heat (which can approach 2000F) is raw fuel being
dumped into the converter because of leaky injectors, faulty O2 sensor,
ignition problems, etc.....if your engine is developing a steady misfire,
DO NOT CONTINUE DRIVING THE CAR!  Converter or engine failure could be
eminent.

		When a converter overheats,  the heat shields will become extremely hot
and could ignite any combustibles touching it or within close proximity
(eg, an out of place fuel hose or leaves on the road).    Eventually, the
ceramic will melt and puddle near the cat inlet blocking the exhaust
flow....the engine will stop running due to the excessive backpressure.  

		BMW does a nice job of engineering their catalytic converters to minimize
fire risk by surrounding the catalyst with heat shields and often
installing shields on the underbody of the car.  BMW's (and all other cars)
are now (96-on) required to have 2 oxygens sensors... one before and one
after the cat.  Significant temperature variances between the two will
trigger a check engine light on the dash.  (Note, early 80's Ferrari's had
an exhaust temp probe to monitor exhaust temperatures).  
		When a catalytic converter goes through meltdown, it must be replaced.
When someone brings back a cat that is discolored due to excessive heat,
the part is generally not covered under warranty as the cause of the
failure originated elsewhere.  SD
 
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Steve D'Gerolamo - The Ultimate Garage
201-262-0412 / steved3@domain.elided / http://www.ultimategarage.com

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