Volkswagen installed plastic sleeves over some of the fuel lines that run through the engine compartment, and there has always been some speculation as to why. Our analysis is that it is for abrasion protection ONLY. These sleeves were constructed of plastic, so heat clearly wasn’t a design consideration. They are open at both ends, which would exacerbate any issues of fluids dripping on them, as the sleeve would hold anything that ran down inside against the hose rather than letting it drip away or evaporate. This leaves abrasion as the primary concern.
We sourced some really nice expandable sleeve material that is rated for use in engine compartments, is flame retardant, is resistant to oils and fuels, has a more-than-adequate temperature rating, and is very affordable.
Each kit contains five (5) 15" lengths of sleeve. One each for the four lines running to the fuel rails and one for the input hose from the firewall to the T-fitting, just like the stock ones. The stock ones were all slightly different lengths, but 15” works well for all locations. Simply slide them onto the end of your fuel hoses when you are installing them and position them so they protect any potential chaffing points. Zip ties are typically not needed but are included as optional insurance against the sleeves shifting around—and so that the ends stay nice and tidy.