The internal combustion engine has seen key advancements over the last few decades, resulting in higher power outputs from smaller displacements. Many engines can now comfortably produce over 100 horsepower per litre, translating to faster acceleration, higher top speeds, and lower fuel consumption. However, increased power generates more heat, and any car with faulty cooling system parts is at risk of overheating.
Engines can reach up to 3,500°F during combustion, enough to melt even the sturdiest metals. Fortunately, meticulous engineering and designs have solved many of the past problems. Heat is managed by engine coolant that circulates through passageways in the engine block, absorbing heat from hot engine parts before reaching the radiator for cooling. To control the flow of coolant, an engine coolant thermostat opens or closes depending on the temperature. The goal is to keep engines at optimal working temperatures (between 200 and 230°F), ensuring maximum efficiency while consuming less fuel.
Cars with damaged, stuck, or faulty thermostats will show signs such as overheating, off-kilter fuelling, power loss, high fuel consumption, and leaks. Mechanics will first check coolant levels and the thermostat’s condition before delving deeper into cooling system defects.
Thermostat Basics
Thermostats have been regulating engine heat since the inception of the internal combustion engine. They are simple yet effective, built around mechanical or electric valves that regulate the flow of coolant in the system by opening and closing based on the engine’s temperature.
Until the car warms up from startup, the engine coolant thermostat remains closed, preventing coolant from circulating. As the engine reaches its ideal working temperature, the valves open, enabling the coolant to do its job. In modern cars, the thermostat works alongside coolant temperature sensors that relay vital information to the ECU, which controls timing and fuelling among other parameters. Engines extract the most power at a defined temperature, enabling efficient combustion cycles.
The mechanism is relatively simple, whether your car has an electronically controlled or mechanical version. Both rely on chambers filled with a wax pellet that starts to melt between 170 and 200°F. The expanding wax engages a spring that pushes a rod and opens the thermostat valve. Circulating coolant can then absorb heat from the block and hot engine parts and return to the radiator for cooling via coolant hoses. If temperatures drop below optimal levels, the valve closes until the desired levels are reached.
Types
There are two basic types found in today’s cars: mechanical and electronic. Mechanical thermostats with an integrated bypass valve still allow coolant to circulate when the thermostat is closed by redirecting it back to the water pump via a water jacket. While effective for most uses, engines with conventional mechanical thermostats are more prone to overheating when cooling system parts fail. They also struggle with efficiency and higher power numbers, so are steadily being replaced with electronic units.
Electrically heated thermostats offer several benefits, including variable operating temperatures to suit different engine loads, quicker response times, and advanced integration with the car’s ECU for improved fuel consumption and lower emissions. There are compatible units that replace worn mechanical thermostats and meet OE and manufacturer requirements. One step up are electrically actuated thermostats, which provide the highest precision in temperature regulation, improved control and performance, and faster warm-up times for reduced engine wear. These are commonly found in many current models.
Signs and Symptoms of Failing Thermostats
Engines that run too hot for prolonged periods will eventually overheat and risk serious or irreparable damage. Conversely, engines that run too cold are subjected to higher wear, reduced performance, and higher emissions and fuel use. Recognising symptoms of a failing thermostat, or the cooling system in general, is crucial in limiting damage. Here’s what to look for:
- Very high engine temperatures – engines that warm up very fast (within a few minutes of starting) often point to a malfunctioning thermostat. Overheating is the obvious sign, usually from a stuck valve that keeps the thermostat in a closed position and prevents coolant from circulating.
- Unstable temperatures – erratic fluctuations between hot and cold are caused by thermostats chaotically closing and opening at the wrong time. This kills performance, increases engine wear and is a forerunner to complete engine failure.
- Inconsistent cabin heating and cooling – malfunctioning thermostats prevent engines from reaching optimal working temperatures, leading to cooler cabins, especially in colder climates.
- Leaking coolant – accompanying overheating is leaking coolant. This is down to a stuck thermostat and ensuing pressure, especially in areas around the thermostat. Untreated leaks and coolant loss with lead to a further rise in engine heat, and the risk of corrosion to surrounding engine parts.
Common causes include general wear and tear, mechanical parts’ faults, metal parts’ corrosion, coolant debris (a worrying sign of other engine issues), and failing gaskets. Repairs are often straightforward, with worn and failing thermostats easily removed and replaced with compatible new units.
Why Consider a Thermostat Upgrade?
While most drivers will opt for OE or certified replacement parts, some manufacturers offer better-built, longer-lasting thermostats for improved engine performance. Upgrading the factory unit, especially in older cars, brings a host of benefits:
- Improved temperature control – high-performance units help with combustion efficiency, with more efficient fuel burns and lower fuel use. Engines are also quicker to warm up, meaning reduced wear from cold starts and improved longevity. They also offer more precise temperature control, preventing overheating.
- Enhance engine performance – engines working at optimal temperatures produce more power, are more responsive to driver input, and have better throttle response. This is despite using less fuel.
- Engine longevity – thermostat upgrades are one of the cheapest ways to ensure your engine lasts longer. Electronic types can also prevent major issues, and save you thousands on repair bills.
- Improved ride quality – consistent engine power when you need it (without fretting about overheating or possible engine failure) is another reason to opt for a high-performance coolant thermostat.
Buy thermostats from reliable car parts manufacturers. The parts are some of the least expensive cooling system components and are widely available. For peace of mind, also have new thermostats installed by a certified mechanic.
