Service Instruction No. 1255 A

Thermostatic Oil Cooler Valve Replacement

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Supersedes Service Instruction No. 1255

May 13, 2016


Lycoming engines using thermostatic oil cooler bypass valve


At 100-hour inspection or when high oil temperature is noted


Updated bypass valve replacement part numbers; added respective detailed bypass valve replacement instructions for engines with oil pressure screens and oil filters

This revision of the Service Instruction identifies thermostatic oil cooler bypass valve P/N 53E22144 (Figure 1) (or other superseding bypass valve identified in the latest revision of Service Instruction SI-1565) as a superseding replacement bypass valve for either bypass valve P/N LW-10269 or P/N 75944.

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