Lesson Plan Industry Sector

Lesson Plan Originally Created By: Dennis Johnson

Thermostat Service/Testing & Replacement (updated) by Dennis Johnson

Part of Unit: Engine Cooling and Lubrication

Lesson Plan Overview / Details

Students will understand thermostat fundamentals.  A stuck thermostat will cause engine overheating (closed) or overcooling (open).  Students will locate, remove, test, and replace a thermostat.

Lesson Time

2 Class Periods
55 Minutes

Objectives and Goals

  • Students will learn thermostat fundamentals
  • Students will properly inspect and test a thermostat
  • Students will learn the procedures for replacing a thermostat

Activities in this Lesson

  • As students enter the classroom, instructor will show a video clip of vehicle with hood up, smoking, steam, coolant leaking etc.  Instructor will have students write down and describe what they think is wrong with the vehicle.  Instructor will give students about 6-8 min to complete this activity while roll is taken.  Instructor will then have a group discussion about this situation to give students an opportunity to share their experience with the class.

    Resources and Materials

  • Instructor will discuss the importance of a properly performing cooling system.  A stuck thermostat can cause engine overheating or overcooling.  If the thermostat is stuck shut, coolant will not circulate through the radiator.  As a result, overheating could make the coolant boil.  If a thermostat is stuck open, two much coolant may circulate through the radiator.  When engine does not reach proper operating temperature, it may run poorly, consequently engine efficiency (power, gas mileage, and driveability) will be reduced.

    Students will be given Chapter 40 (Cooling System Testing, Maintenance, and Repair theory work) which will discuss principles of heating and cooling (thermodynamics) and how the cooling system is extremely important to the performance and service life of an engine. Major engine damage can occur in minutes without proper removal of excess combustion heat.

    Instructor will show video clip on cooling system safety.  Care must be taken when servicing the cooling system. Parts can heat up very quickly and hot coolant under pressure could scald/burn student very easily.  Instructor will also show video of how to safely remove and install a thermostat.  Instructor will give students inspection sheets, one to complete during the lecture session and the other will be utilized in the lab.  Students will follow along and take notes during this session to use them and the inspection sheets as a reference during their own thermostat replacement.  Instructor will answer any questions that may arise during this session.

    Resources and Materials

  • Thermostat Removal Demo / Modeling

    Instructor will have the students get their safety glasses, sample inspection task worksheets, and the remaining blank inspection sheet, and follow instructor into the shop for a demonstration on how to perform a thermostat service.

    Instructor will now demonstrate how to replace the typical thermostat.  CAUTION: Make sure the engine is cool to prevent personal injury from hot coolant.

    1) Place approved coolant drain bucket under radiator, remove drain plug or lower radiator hose to allow coolant to drain.

    2) The thermostat is normally located in thermostat housing at the engine end of the upper radiator hose.  Thermostat is removed by unbolting the thermostat housing bolts, light taps or prying will free the housing.  Be careful not to damage the thermostat housing.

    3) Lift off the housing and thermostat.  Now scrape all the old gasket material and sealant off the thermostat housing and the sealing surface on the engine.  Be careful not to gouge or nick the sealing surface or leakage may result.

    4) Inspect thermostat, note the temperature rating.  Make sure the temperature rating of the new thermostat is correct for the engine.  Install new thermostat in the engine, the rod (pointed end) on the thermostat should face the radiator hose, and the pellet chamber should face the inside of the engine.

    5) Position the new gasket or rubber seal instead of gasket on some engine designs.  Start the fasteners/bolts by hand.  Then torque them to specifications in a crisscross pattern.  Do not overtighten the thermostat housing bolts.

    NOTE: With some engines, the thermostat housing, cooling system filler neck, radiator hose nipple, and overflow tube are all combined into one housing made of plastic. Do not damage it while working. 

    Resources and Materials

    • Thermostat Task Worksheet [ Download ] Hands on Lab Skills Work Sheet
  • Instructor will have students form into groups of two (2), assign them a vehicle and ask them to locate the upper radiator hose and thermostat housing.   Once students have done this, instructor will ask students to follow the procedures demonstrated to them and now remove, inspect and replace the thermostat.  Students will indicate condition of thermostat, the thermostat housing, and perform a visual inspection by checking for leaks, and any physical damage to the hose or hose clamp.  Instructor will ask students to record their findings on the inspection sheet during this task. During the inspection and after they have completed their forms, instructor will have student teams perform spot inspections on the other teams work and documentation.

  • Clean-Up Closure

    Instructor will have students put away all checked out tools, clean up their work area, secure the vehicles, and asks students to wipe up all coolant spills and properly dispose any dirty shop towels. Instructor will discuss the importance of cleaning up their work area and checking tools back to the tool room.  Instructor will verify that students work was done and meets industry standard.  Instructor will discuss the following items:  Did students get it and where they able to perform the thermostat removal and installation? Instructor will inform students that we will continue with procedures to diagnosis, inspect and service the cooling system.


Assessment Types:
Demonstrations, Observations,

Instructor will monitor the students during the lecture, modeling and group work components and ask questions about the material being taught to ensure students understand the information.  Instructor will monitor the students in the lab and ensure that they are following shop safety as well as answer any questions that may arise.