Green antifreeze or coolant as some call it.

I use this Green, available at Autozone stores. See the last line below...
AutoZone green is a conventional ethylene glycol based antifreeze for use in older automotive and light duty diesel applications.

• Provides year-round protection against damaging rust and corrosion
• Compatible with all conventional green antifreeze
• Protects all metals, including aluminum
• For use in all makes and models 1989 and earlier