Service Bulletin No. 518 D

Inspection of Thermostatic Oil Cooler Bypass Valves

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August 16, 2016

MODELS AFFECTED

All Lycoming engines with thermostatic oil cooler bypass valves: Part number (P/N) 53E19600 (with thermostatic oil cooler bypass valve serial numbers less than 53788), P/N 75944, P/N LW-13230, and P/N 53E19980 (with thermostatic oil cooler bypass valve serial numbers less than 159)

TIME OF COMPLIANCE

At the next oil change, not to exceed 50 hours, then annually thereafter

REASON FOR REVISION

Identified new superseding thermostatic oil cooler bypass valve and updated corrective action after inspection; valve rework/repair is no longer allowed.

This Service Bulletin contains instructions for a mandatory inspection of the crimp nut on the thermostatic oil cooler bypass valve on affected Lycoming engine models. This required inspection is in response to field reports of loose crimp nuts that can drop into the engine and cause engine damage. The required inspection herein ensures that the crimp nut (Figure 1) is securely seated on the shaft.

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