Remember.... You can lead a horse to water, but a pencil must be lead.
Anyways, no full gas tank will ever explode. Gas itself does not explode, the air vapor heavy with gas fumes will. If you have a half full tank or an empty tank, you might get an explosion with an incendiary round. Otherwise, you may just puncture it, have the gas leak out, then be set afire AFTER leaking out (on hot radiators, more bullets causing sparks, electrical wires, etc).
Tracer bullets are not incendiary. There were different chemicals used to make the bullets glow different colors (reds vs greens etc). The bullet wasn't "on fire", but rather the heat from the firing process makes the material coated over the bullet glow. This gives you the smoke dust trail and the glow so you can track the motion of the bullet.
I'm pretty sure the temperature of a tracer is not much more than any other massive chunk of lead and steel traveling many times the speed of sound, after being ejected out of a confined tube with a powerful fiery explosion.
As for US planes, most of them used API throughout the war. Better chance of igniting flamable materials.