I while back someone posted the stl file for printing a fuel return block. I’m unable to find the post so going of memory I don’t remember him talking about which filament should be used, but I could be wrong.
Unless you specify the correct filament it will most likely be printed with PLS. It will start to soften at 120 degrees.
I use Carbon Fiber PETG-CF. It is a high-performance engineering thermoplastic, and fortified with carbon fiber, this filament is an engineered Metal-Like Strength to excel in high-stress applications, offering superior toughness, chemical resistance, and thermal stability. It performs well in continuous service temperatures up to 392–428°F and resists exposure to fuels, oils, and industrial chemicals. This combination makes it ideal for automotive and high-temperature functional parts. Carbon fiber reinforcement also reduces warping and improves surface flatness, making printed parts more reliable and precise for functional applications.
I had a couple print up with PETG-CF and selling them for $50.00 including USPS shipping. Contact me though the forum or email at jeff@fisherresource solutions.com

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2006 KJ CRD AMSOIL Fluids, AMSOIL Oil Filter, AMSOIL ByPass Filter, Secondary Fuel Filter, Provent, Silicone Hoses, Rotomaster Turbo
2013 Audi A3 2.0 TDI Premium Plus
1948 T4 Willis Pickup
1993 C3500 Chevy 6.5 Turbo Diesel
1984 C7500 Chevy Flat Bed 366 gas
1987 R25 Chevy 350 gas