Surprising Insights to Your Engine Thermostat

Several recent repairs at Tierra Del Sol Automotive have been related to thermostat operations and most have ended with service to replace it. 

So, what is an engine thermostat and what does it do, you ask? It’s quite a simple answer and may surprise you as to how it operates. Simply stated, the thermostat is a mechanical blockage in the cooling system designed to keep engine coolant within the passages located in the engine block and cylinder heads and not allowing that coolant to escape and be cooled by the engine radiator. 

That seems silly you say? Why would we want to block the coolant from performing its job of cooling the engine? This answer is not quite as simple as the first, so bear with us here.

All cars manufactured today have to adhere to strict government regulations regarding tail-pipe emissions. So when your car engine is operating it has to produce acceptable levels of exhaust gases as outlined in the emission regulations set for USA operating vehicles. 

Great! But what does that have to do with my thermostat?

A little understanding of your cars engine operation is needed to answer that very question. When a car engine is cold – say after sitting in your garage all night – and you want to start it first thing the next morning, the amount of fuel needed to get and keep a cold engine running is much higher than a warm engine. More fuel being introduced into the engine results in higher fuel emissions coming out of the tailpipe. Higher emissions into the atmosphere is a bad thing because it deteriorates the ozone layer that protects the earth. So, if we block off coolant and keep it in the engine without moving, it heats up quicker – due to lack of movement into the radiator – and reaches engine operating temperature much faster than an engine without a thermostat. 

Once the engine reaches a predetermined coolant temperature (that the engine reads from a sensor in the coolant), fuel control is adopted by the engine computer to burn at a precise mixture to eliminate excessive pollutants entering the atmosphere. 

Automotive engineers have extensive research identifying a maximum time allowed to reach the operating temperature for your particular engine. At first startup, the computer begins counting, in seconds, how long it takes for your automobile to reach that pre-set temperature. If it fails to reach the operating temperature within the allotted timeline (two or more times in a row), the Malfunction Indicator Light (aka, Check Engine or Service Engine Soon Lights) is/are illuminated. 

How exactly does this thermostat operate? You said it is mechanical right? 

That is correct, a thermostat is mechanical Most engines, generally speaking, have a thermostat rated between 180-195 degrees Fahrenheit which is specific to your engine size.

The thermostat is normally located in the “thermostat housing”, normally near the engine block at the upper radiator hose, but not always.

Each vehicle manufacturer will have their own designs and locations. This thermostat operates using spring pressure and wax pellets. Mechanical spring pressure holds the thermostat closed when the engine coolant is below the specified temperature. As the wax pellets, which are designed to melt into a liquid, the wax expands and pushes on a rod that allows the thermostat to open thereby allowing hot coolant to flow out the engine through the hoses and into the radiator to be cooled. 

But we don’t want the cold coolant to cool the engine off again, do we? 

No, we don’t want the engine cooled. Let’s clarify what temperatures we are talking about once the coolant is cooled. Engine coolant that is cooled remains above thermostat opening temperatures and range anywhere from 190-210 degrees or more on a normally operating system. 

That doesn’t seem very cool! 

We want the engine to perform optimally and to be producing as little emissions as allowable. And that seems to be the most desirable engine operating temperature of most automobile engines, thereby producing minimal exhaust emissions. 

Temperatures too low end up producing high emissions and costly fuel consumption while engines running too hot cause excessive emissions and potential damage to your engine. 

Come into Tierra Del Sol Automotive and ask us to inspect or replace your thermostat if you encounter poor fuel mileage, engine overheating, a check engine light on or an engine that doesn’t seem to warm up quickly. (An engine that doesn’t seem to warm up quickly is typically an example of a stuck open thermostat.)

Our ASE Certified Technicians can perform a thermostat health check for you and provide you with graphed images and temperature ranges showing you EXACTLY when and at what temperature your thermostat opens after engine startup. 

Drop by, or give Tierra Del Sol Automotive a call 575-443-1880. Your automobile will thank you!