Jeep first released the Wrangler in 1987 as the replacement for the CJ series. The first generation of Wranglers, from 1987 through 1995, were known as the TJ generation. The 1995 Wrangler, the last year of the TJ generation, came standard with a 123-horsepower 2.5-liter engine, but had a 180-horsepower 4.0-liter as an option. Both engines are cooled by a mixture of anti-freeze and water. The thermostat acts as the gatekeeper for the mixture and only allows it to flow into the engine as needed. When this thermostat fails, the Jeep can either overheat or over-cool.
Raise the front of the Wrangler with a floor jack and place jack stands under the frame rails. Lower the floor jack until the Wrangler's weight is held only by the jack stands.
Crawl beneath the Wrangler and locate the petcock -- the radiator drain plug -- on the lower, passenger side of the radiator. Slide the drain pan under the petcock. Remove the petcock with a ratchet and socket and allow all of the coolant to drain from the radiator. Tighten the petcock back into the radiator.
Trace the upper radiator hose until it meets the engine. The metal connection point between the radiator hose and the engine is the thermostat housing. Remove the two bolts securing the thermostat housing to the engine and pull the housing off of the engine, exposing the thermostat below it.
Grab the thermostat and gasket and pull them from the engine. Scrape off any remnants of the gasket from both the engine and the thermostat housing.
Insert the new thermostat into the engine, with the spring portion facing the inside of the engine. Slide the bolts through the holes in the thermostat housing and place the thermostat gasket on the bolts to hold it in place.
Sit the thermostat housing and thermostat gasket and over the thermostat. Tighten the thermostat housing bolts to 13 to 15 foot-pounds, using a torque wrench and a socket.
Open the radiator cap and fill the radiator with 50/50 premixed coolant. Start the Wrangler and allow it to warm up to its normal operating temperature. Observe as the coolant level falls once the Wrangler warms up and the thermostat opens -- this is the coolant circulating through the engine.
Add coolant each time the level drops. Repeat until the level in the radiator remains steady.
Watch the coolant in the radiator and check for bubbles coming to the surface. This allows all of the air to burp from the cooling system.
Tighten the radiator cap and shut down the Wrangler's engine once no more bubbles appear in the system.
Raise the Wrangler from the jack stands using a floor jack and pull the stands from under the Jeep. Lower the vehicle to the ground.
Allow the engine to cool and check the coolant level in the coolant reservoir. The level must be between the "Min" and "Max" lines, add 50/50 premixed coolant to the reservoir as needed. The entire cooling system for the 2.5-liter takes approximately 2-1/4 gallons, and the 4.0-liter's system takes approximately 2-1/2 gallons.
Close the Wrangler's hood.
