How To Change a Car Thermostat and Fix Overheating

It can happen even on a cold day: your car’s temperature gauge slowly starts to creep up, entering the red zone. Red definitely means danger, so to avoid the risk of frying your engine and popping a head gasket, you pull off to a safe place and shut the engine down. But what now?

If you’re not losing coolant due to a leaky radiator hose, your problem likely lies in either a stuck thermostat or the engine’s water pump. Luckily, a car thermostat is easy to change. Foremost authority on all things Jeep, BleepinJeep, produced a how-to video with instructions on how to change a thermostat. As always, safety should come first. Never open a radiator cap while the engine is hot. In fact, it’s best to wait several hours after turning off the engine to prevent the risk of pressurized coolant spraying from the system. Safety glasses and gloves are a must. Once the car is cooled off and you’re geared up, pop the hood and get started.

First, locate the radiator drain plug from the bottom of the radiator, be prepared for splashes, and capture the coolant for recycling. Locate the thermostat housing, usually located at the engine block near an upper radiator hose. Unclamp the hoses, unbolt the thermostat housing and remove the thermostat, taking note of its orientation and how it is placed in the housing.

If a previous mechanic placed RTV sealant on the thermostat housing mating surfaces, remove it carefully, making sure not to nick other lines or hoses underhood and taking care not to let any particles enter the cooling system. Many thermostats come with thermostat housing gaskets, removing the necessity for RTV sealant. Place the new thermostat in its housing, ensuring correct orientation, with the air bleed holes facing upward. Bolt in the thermostat housing, replace the hoses and clamps, ensure the drain plug petcock is in place and refill the cooling system through the radiator filler neck using the proper grade and amount of coolant recommended by the vehicle’s owner’s manual.

If you’re using undiluted coolant and need to dilute the coolant yourself, create a 50/50 mix using distilled water only. Regular water has minerals that can leave harmful deposits in your cooling system. Fill the radiator overflow bottle to the proper level, and with the radiator cap off, start the engine. Let the engine rise to temperature, and ensure that the engine does not overheat. If no overheating occurs, you’ve fixed the problem with a new thermostat! You’ll see bubbles plop out from the radiator filler neck as air is bled from the cooling system. The coolant is scalding hot, so take care not to get splashed. Once the air is out of the system, refill to capacity and cap the radiator.

Air in the system will reduce cooling efficacy, so ensure all of the air is out of the system. It’s a good idea to check the coolant overflow reservoir level a few times after servicing the system, and you may want to carry some coolant during your first few trips just in case. Replacing a stuck thermostat is an easy way to solve many engine overheating issues — and it’s a job you can do yourself with parts from Pull-A-Part!

Source: BleepinJeep