B737 captain reported decreasing oil quantity on right engine at cruise with subsequent fluctuating ...

Narrative:

In cruise at FL380. Noticed right engine oil quantity indicated 4 qts. Went to QRH and followed procedure. Oil pressure and temperature indications were normal and pretty much matched the left engine. Continued to monitor as directed. Called dispatch on crew phone ( which worked great btw) and gave him a heads up. Agreed that we would continue with diverts ahead of ZZZ; ZZZ1 and ZZZ2. Quantity indication continued to decrease slowly over the next hour. Pressure and temperature were normal. Approximately abeam ZZZ1 we asked to descend to fl 300 due to turbulence. At idle power; oil pressure and temperature remained normal and basically matched the left engine. However; at level off when power was increased; we noticed that the right engine oil pressure began to noticeably fluctuate and decrease. We immediately [advised] with ATC and began a diversion to ZZZ2. With right oil pressure at or near the red line limit; we elected to shut down the engine. Complied with QRH procedures and executed an ILS/visual single engine approach to runway 26. Arrf was standing by. We cleared the runway and stopped on the parallel taxiway. Arrf crew checked out the right engine and advised that there were no issues. They followed us to gate A-9. Maintenance met us at the gate and were debriefed.

Original NASA ASRS Text

Title: B737 Captain reported decreasing oil quantity on right engine at cruise with subsequent fluctuating pressure and quantity resulting in an inflight engine shutdown and diversion to make an priority landing.

Narrative: In cruise at FL380. Noticed right engine oil quantity indicated 4 qts. Went to QRH and followed procedure. Oil pressure and temperature indications were normal and pretty much matched the left engine. Continued to monitor as directed. Called dispatch on crew phone ( which worked great BTW) and gave him a heads up. Agreed that we would continue with diverts ahead of ZZZ; ZZZ1 and ZZZ2. Quantity indication continued to decrease slowly over the next hour. Pressure and temperature were normal. Approximately abeam ZZZ1 we asked to descend to FL 300 due to turbulence. At idle power; oil pressure and temperature remained normal and basically matched the left engine. However; at level off when power was increased; we noticed that the right engine oil pressure began to noticeably fluctuate and decrease. We immediately [advised] with ATC and began a diversion to ZZZ2. With right oil pressure at or near the red line limit; we elected to shut down the engine. Complied with QRH procedures and executed an ILS/visual single engine approach to RWY 26. ARRF was standing by. We cleared the runway and stopped on the parallel taxiway. ARRF crew checked out the right engine and advised that there were no issues. They followed us to gate A-9. Maintenance met us at the gate and were debriefed.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1740051
Time
Date	202003
Local Time Of Day	1801-2400
Place
Locale Reference	ZAB.ARTCC
State Reference	NM
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Powerplant Lubrication System
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

B737 captain reported decreasing oil quantity on right engine at cruise with subsequent fluctuating pressure and quantity resulting in an inflight engine shutdown and diversion to make an priority landing.