I noticed that since my 124 engine compartment is sealed up so well that when I used the heater the whole compartment warmed up. Not just a localized area of the engine.

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1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png