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You can damage the engine spraying cold water on a hot engine in some cases! It's not bunk.
The old OM61x iron-head engines seem pretty impervious to damage and I've
not heard of one acting up after a cold wash on a hot engine. HOWEVER, the
OM60x engines with aluminum heads are a different story! Even after letting
it cool so the dash gauge was down to 50-60C, I got frightening cracking and
popping noises when using the high-pressure rinse at a coin-op car wash.
Sure enough, I ended up with a few drops of oil in the coolant, which really
really pissed me off (NEW head and gasket less than 10kmi earlier). The oil
amount was tiny, so I torqued the head bolts in sequence another 1/8 turn
each, and so far that has seemed to cure it. Had a similar problem with the
old head & gasket as well. Don't screw around with aluminum head engines. My
trick is to drive the car to the car wash, put the heater on MAX, then kill
the engine but leave the key on. The electric auxiliary coolant pump will
force coolant through the heater core and the fan on MAX will cool the
engine significantly inside 15-20 minutes. Leave it like that while you're
jacking up one corner of the car (for better access to the underside), and
spraying Engine Brite on everything. Then rinse it.
Side note: The 3-prong temp switch on OM603 engines, that triggers the
electric radiator fan in front of the condenser, DOES NOT like to get wet.
If you spray it with water, IT WILL switch on and may not ever switch off.
This has happened to two of my switches personally, plus at least 2-3 other
people I know of - in all cases a new switch cured the problem. Simply
placing the plastic cap from the Engine Brite can over the switch, to
prevent *direct* spray on it, prevents the problem. But don't think
everything electrical in the engine compartment is impervious to water
spray - that just ain't true!
Dave Meimann
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