Related Clues:

• Explorer's need
• With 40-Down, H+, e.g.
• Fun time
• Car fuel
• Highway sign word
• It's in a certain range
• It may be noble
• Tummy woe
• Auto additive
• Idle talk
• Pretentious talk
• Helium, for one
• Hydrocarbon fuel
• What to 'fill 'er up' with
• The 'it' in 'Step on it!'