What is the melting temperature of a 3D printed part?
The number you're looking for is the glass transition temperature (the lowest temperature at which the material can flow or warp), not the melting point.  This depends on what material you're using; approximate temperatures for common printable materials are:


PLA: 60˚C
PETG, high-temperature PLA: 95 ˚C
ABS: 105˚C
Nylon: typically 70˚C or above ("Nylon" is a large family of similar polymers)
Polycarbonate: 145˚C


Any plastic under your hood is probably either nylon (for its durability, impact resistance, and chemical resistance) or ABS (for its strength and heat resistance).  These are both difficult materials to print: ABS emits toxic fumes while printing, and tends to warp if you're not using a heated enclosure, while nylon readily absorbs water from the air, causing the filament to bubble as it's printed.  Further, many printers can't handle the high temperatures needed to work with these materials.

If you're going to print this yourself, I recommend using PETG and inspecting the part after a few days of use to see if it's warping.  PETG is reasonably easy to print and comes close to your target heat resistance.

If you're going to get someone else to print it, I recommend using ABS.  It's probably what the original part was made of, and anyone willing to print ABS for you will have the heated enclosure and ventilation system to deal with printing it.

I'd avoid polycarbonate unless you know the original part was made of it.  Although PC is strong and heat resistant, it's also somewhat brittle and vulnerable to scratching.

High-temperature PLA is also brittle, and requires a heat-treating step that will change the dimensions of the part.  It will likely take several tries to get something that comes out the right size, and even then, you risk having the part break when your car hits a bump.