Thermostat Replacement

Covers:

• 1990-1992 3.0L V-6 Engine

Thermostats control the temperature of the engine coolant. This can effect engine operation, performance, and the heating system. If a thermostat is stuck open or opens prematurely, the coolant temperature will stay too cool, affecting the air/fuel ratio as well as the heating system. Symptoms include poor heating by the climate control system. If a thermostat is stuck closed or stays closed past the specified temperature, the engine can overheat, causing poor engine performance and and possible engine damage. Many people unfamiliar with engine maintenance or operation don't know what the thermostat does nor even where it's located. This causes the thermostat to be often overlooked when diagnosing coolant system problems.

Changing the thermostat is relatively easy and very inexpensive. Most thermostats cost between $5 and $10, also with a gasket which usually costs less then $2.

Overview

The thermostat is located in the thermostat housing. The housing is where the upper radiator hose connects to the engine (see Image #1, below). DO NOT service the coolant system until the engine cools.

Parts Required

• New thermostat (195° F)

• New thermostat gasket

• Coolant

Tools Required

• 10mm wrench/socket

• Scraper or razor blade

• Torque wrench

Removal

1. Remove the radiator cap. Place a bucket or pan under the radiator drain plug (bottom of radiator, toward passenger side) and drain the coolant.

2. Replace and hand tighten the radiator drain plug.

3. Remove the clamp from the upper radiator hose at the thermostat housing and disconnect the hose.

4. Remove the 10mm nut from the thermostat housing which holds the wiring harness bracket and ground wire in place. Move the wires and bracket aside.

5. Remove the two 10mm bolts and stud from the thermostat housing and remove the housing. It may stick, so light prying may be required, but be careful not to damage the housing or cylinder head rear housing.

6. Remove the thermostat from the thermostat housing.

7. Using a scraper or razor blade, carefully clean all the old gasket material from the thermostat housing and the cylinder head rear housing. Make sure the surfaces are clean and smooth to assure proper sealing when reinstalled.

Installation

1. Place a new thermostat into the thermostat housing. The jiggle pin should be at the top and aligned with the recess at the top of the thermostat housing. The side with the spring should be facing the engine.

2. Position a new gasket and install the thermostat housing, tightening the three bolts to 8-10 ft/lbs.

3. Reinstall the wiring harness bracket and ground wire on the thermostat housing stud an tighten the nut.
4. Reconnect the upper radiator hose and replace the clamp.
5. Refill the radiator with new coolant (50/50 mix of coolant and water).
6. Fill the coolant reservoir with coolant up to the 'FULL' line.
7. Install the radiator cap and turn the cap to the first stop.
8. Start the engine and allow it to warm. Shut off the engine once the upper radiator hose feels warm (indicating the thermostat has opened).
9. Check the coolant level and add if required.
10. Tighten the radiator cap fully (second stop).

Notes

• Do not reuse old coolant. Replenish the coolant system with new coolant only.
• Use a 50/50 mixture of coolant and water. More water can be added for slightly improved cooling (55/45 mixture), but do not exceed a 60/40 mixture.

Image #1