A 1990 Jeep Wrangler with a 5-speed manual transmission doesn't use automatic transmission fluid (ATF). It uses
gear oil. The specific type and weight will depend on the climate where you live and the specific recommendations in your owner's manual. However, a common and suitable choice is
75W-90 GL-4 gear oil.
Always check your owner's manual for the manufacturer's specific recommendation. Using the wrong type of lubricant can damage your transmission.
