Ah, the serial number conundrum...explained.
The yellow is Model 3500 and the blue is Model 3510.
The yellow motor housing was molded from a slightly paler yellow plastic of a different composition. The tank & nozzle are of a tougher durable Cycolac type that perfectly matches the paint on the metal 'landing gear' trundle. while the motor is encased in a softer vinyl-ized plastic that mars easier. Every yellow one I've seen has this subtle two tone look - the blue seems to have corrected this visually to a greater extent tho under bright light it too has a slightly lighter motor.
About a year ago there was a Floor Washer Owners manual on Ebay but the winner could afford to want it more than I. :-(
Any scanned material on the Hoover Floor Washer would be greatly appreciated, especially the Manual.
Dave
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