Why replace your thermostat?
The thermostat has two important jobs to perform: to accelerate engine warm-up and to regulate the engine's operating temperature. A quality thermostat ensures excellent fuel economy, reduces engine wear, diminishes emissions, improves cold weather drivability, provides adequate heater output to keep you warm and comfortable while driving and detours engine overheating. This is accomplished by blocking the circulation of coolant between the engine and radiator until the engine has reached its predetermined temperature.
The thermostat then opens as required in response to changes in coolant temperature to keep the engine's temperature within the desired operating range. Thermostats have a rated temperature such as 180°F or 195°F depending on make and model. This is the temperature the thermostat will start to open, give or take 3 degrees.
The temperature rating specified by the car manufacturer is especially important in many 1981 and newer vehicles because the onboard computer monitors coolant temperature through a coolant sensor to control fuel enrichment, spark timing and operation of the EGR valve. Even on vehicles without computers, thermal vacuum switches that react to a specific coolant temperature are often used to open and close various vacuum circuits that regulate fuel enrichment, timing and EGR. If a colder thermostat is installed, the coolant may never get hot enough to trigger the appropriate control functions or to allow a computer system to go into “closed loop”. Too hot a thermostat can also interfere with the proper operation of engine controls, and increase the engine’s operating temperature to the point where it may experience detonation (spark knock).
Tools and equipment
To remove and install a thermostat, you will need:
- A clean rag
- New thermostat
- Gasket and gasket sealant
- Screwdriver or pliers
- Small socket wrench
- Small adjustable wrench
- A small scraper or wire brush
- 9 L bucket or drip pan
Before you begin
Proper maintenance and service procedures are vital to the safe, efficient operation of all motor vehicles, as well as to the safety of the person performing the work - you. Whenever you are working on your vehicle, we recommend that you follow these important safety rules:
- Do have a first-aid kit handy.
- Do be careful when working around hot or sharp objects.
- Do follow the manufacturer's instructions for all products.
- Do use safety stands under the frame or drive-on ramps if you must raise your vehicle.
- Don't run the engine without proper ventilation.
- Don't smoke when working around the engine.
- Put the car on level ground. Always wait until your engine is cool before working on any part of your car’s coolant system. Drain the cooling system. If you are flushing and cleaning the radiator and cooling system, do this before you change the thermostat.
- Remove the radiator hose attached to the thermostat housing by using the screwdriver or pliers to pull off the clamp.
- Twist the radiator hose to loosen it from the thermostat housing. Use a spray lubricant if the hose is difficult to loosen. Be aware that a considerable amount of coolant will pour out of the hose when you take it off. Loosen the bolts on the thermostat housing with the appropriate sized ratchet socket or open-ended wrench. Lift the cover off and remove the thermostat. Temporarily stuffing a clean rag into the thermostat opening on the engine while the housing is removed helps keep debris out of the cooling system.
- Look at how the thermostat is positioned and remember to put it back the same way. Install the new thermostat so the copper heat sensing element is toward the engine. If installed upside down, it won’t function properly.
- Inspect the accessible part of the water jacket for corrosion. Carefully remove any thick crusted corrosion but do not let it drop inside the water jacket. Also clean the rims of the thermostat housing from old gasket or glue remains. Use the putty knife or scraper to remove the old gasket from the thermostat housing and cover base. Use care on aluminum housings because the soft metal can be easily scratched. 6. Put on a new gasket and replace and tighten housing. Torque the thermostat housing bolts evenly and to the manufacturer's recommendations.
- Re-attach the hoses and put the engine coolant back into the vehicle. When everything is back in place, run the engine to full operating temperature and check for leaks and ensure air has been removed from the cooling system.
- Take the car for a drive and check that the temperature gauge needle stays at normal with the car at full operating temperature. If the needle did not do this before you changed the thermostat, it should do so now.
- After your drive, make a final inspection for coolant leaks and levels.
- Follow these instructions carefully. Read and be sure you understand them before you begin.
- Gather all your tools and supplies before you begin.
- Allow plenty of time to do the job so you don't have to hurry.
- Remember that these are general instructions. For more detailed instructions pertaining to your specific vehicle, consult an appropriate repair manual.
- Safety is important whenever you're working around machinery. Beware of hot objects, sharp instruments and hazardous materials.
- Don't substitute tools unless you're sure it won't compromise either your safety or the performance of your vehicle.
- If you have any questions about repair and maintenance, contact your local NAPA Auto Parts store. Find the nearest NAPA Auto Parts location.