The bypass valve setting and flow rate are the critical differences, aside from basic dimensions. The 500 has a lower bypass pressure and a lower flow rate than the 820.
It would seem that they should not be interchanged.
Here is a snippet from another enthusiast forum:
http://www.fordfusionclub.com/index.php?...2227#msg3162227
Motorcraft Number FL500s
Part Number: 57502
Principal Application: Mazda Tribute, Ford Escape and Mercury Mariner (2009) w/ 3.0L engine - Ford Taurus, Edge, Mercury Sable w/ V6 3.5L mfg after 1/16/2009
Style: Spin-On Lube Filter
Service: Lube
Type: Full Flow
Media: Paper
Height: 4.09
Outer Diameter Top: 2.942
Outer Diameter Bottom: Closed
Thread Size: 22X1.5 MM
By-Pass Valve Setting-PSI: 8
Anti-Drain Back Valve: Yes
Max Flow Rate: 10-12 GPM
Beta Ratio
Burst Pressure
Normal Micron Rating
Gasket Diameters
OD 2.753
ID 2.397
THK 0.25
Motorcraft Number FL820s
Part Number: 51372
Principal Application: Ford/Lincoln/Mercury (91-09), Mazda (00-09), Cadillac STS-V, XLR-V (06-09)
Style: Spin-On Lube Filter
Service: Lube
Type: Full Flow
Media: Paper
Height: 4.167
Outer Diameter Top: 3.66
Outer Diameter Bottom: Closed
Thread Size: 22X1.5 MM
By-Pass Valve Setting-PSI: 16
Anti-Drain Back Valve: Yes
Max Flow Rate: 11-13 GPM
Beta Ratio 2/20=12/25
Burst Pressure 275
Normal Micron Rating 19
Gasket Diameters