I have had the caps fall out for no apparent reason several times. So I installed caps that have hinged doors then installed screws to make permanent (cut/filed the screw tips down on the inside so they didn't catch on the hose).
Dale & Terri, Lulu & Tiki (our Chihuahua's), New rescue puppy Prince - Pom/Pug mix.
2013 Tundra, Double Cab, 5.7, TRD Off-Road, 4X4, Full Tow Package
2013 Wildwood T26TBSS - Sold
2000 Gulf Stream Sun Voyager M-8357 MH, Ford Trident V10 Gasser, 35 foot.