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Jeep Grand Cherokee 1999-2004: How to Replace Thermostat

A faulty thermostat in your Jeep Grand Cherokee can't allow the coolant from going into your engine, resulting in an overheating engine. Learn how to replace it here.

By Bassem Girgis - October 2, 2015

This article applies to the Jeep Grand Cherokee WJ (1999-2004).

The thermostat in your Jeep Grand Cherokee works as a gate between your radiator and engine. When you start your car, the thermostat blocks the coolant from going into your engine until the engine is hot enough, then it opens up and allows the coolant to go into the engine to keep it from overheating. Even though the thermostat is a small looking device, it's the gate between an overheating engine and a healthy one. If the thermostat is faulty, it won't open when the engine reaches the optimal temperature, which will let the engine continue heating up with no coolant to keep it cool, thus overheating. Replacing it is both cheap for your wallet and time. Read on to learn how to replace your thermostat.

Figure 1. The thermostat.

Materials Needed

  • Ratchet and socket (10mm)
  • Tray or container
  • Flat head screwdriver
  • New thermostat with its gasket and adhesive

Step 1 – Drain the coolant

Open the hood, open the radiator cap on top of the radiator, and locate the drain plug on the bottom of the radiator on the passenger's side. Place a container under the drain plug and remove the drain plug, letting all the coolant drain from the radiator. Tighten the drain plug.

  • Figure 2. Locate the plastic drain plug.
  • Figure 3. Drain the coolant.

Step 2 – Remove the thermostat

Locate the upper radiator hose. It goes from the top of the radiator to the thermostat assembly. Remove the clamp on the edge of the hose on the thermostat side. Remove the hose by pulling it out. Keep a rag underneath it to avoid any small spills.

Using your 10mm socket, remove the two bolts holding the thermostat assembly in place. Pull the cover off and remove the old thermostat.

  • Figure 4. Remove upper radiator hose.
  • Figure 5. Remove the thermostat.

Step 3 – Install the new thermostat

Install the new thermostat the same way the old one was removed. Scrape off the old gasket from the cover, and install the new gasket in its place by spreading a thin layer of gasket adhesive where the gasket sits. Install the cover on top of the gasket and tighten the two bolts. Reattach the hose to the thermostat assembly and tighten the clamp.

Figure 6. Thermostat location.

Step 4 – Refill radiator

Refill the radiator with coolant until it reaches the top. With the radiator cap off, start the car and let it run for a few minutes, then top off the coolant. Keep an eye on the coolant's level for a few days after that and top of as necessary.

Figure 7. Radiator's proper level.

Featured Video: Thermostat Replacement

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