"injection pump $100 obo mercedes om636 thermo king"

Thermo King, indicates it came from an Engine that was used on a Generator set. The gen sets were attached to the Chassis (Trailers) on which Refrigerated
Containers go to power the Refrigeration.

My last Mechanics job was working for a Refrigerated Container company. In 1989 an occasional Thermo King with the Mercedes Engine would come in (Thermo King also used other Engines).
But, most of the newer gen sets had Mitsubishi or Kaboto Engines.
A lot of the Carrier gensets in use had 3 cylinder Air Cooled Engines on their Gen Sets but I never did learn what make of Engine they were. Other than changing Oin and Filters the Air cooled Engines caused no issues that I can remember.

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84 300D, 82 Volvo 244Gl Diesel