NWACHUKWU AUTO-TECH
What are the Thermostats?
The thermostat is used to control the minimum operating temperature of the engine so that overcoming is prevented. |
| Diagram of a thermostat |
A CAR THERMOSTAT DIAGRAM
An overcooled engine wastes fuel and wears out at an abnormally fast rate. Also, computerised ignition cars do not run in the normal operating mode until the coolant sensor is at normal operating temperature.
The thermostat is the key component of the engine cooling system. The cooling system keeps the engine from overheating. The system is filled with liquid coolant (antifreeze) and is connected into a loop with a radiator.
A thermostat temperature-controlled valve is placed at the engine coolant outlet to restrict coolant flow until the engine reaches the operating temperature of the thermostat.
When the thermostat is open(hot), coolant flows from the water jackets to the radiator and when it is cold, it stops the flow to or from the radiator.
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HOW A THERMOSTAT WORKS:
One or two electric fans attached to the back of the radiator turn on when needed to force more air through the radiator.
A water pump pulls the coolant out of the radiator and pushes it back into the engine.
How the thermostat works in the car Thermostat is closed:When the engine is started cold, the thermostat (the main valve) is closed; there is no flow through the radiator. The smaller thermostat bypass valve is open and the coolant circulates through the bypass tube within the engine and through the vehicle's heating system. This allows the engine to warm up faster.
Thermostat is open:
As the engine warms up closer to the operating temperature, the thermostat valve gradually opens up, allowing coolant to flow through the radiator. Thermostat Open diagramThermostat is openThe coolant enters the top portion of the radiator and cools down as it flows through the radiator. The water pump pulls the cooled coolant back into the engine.
In cold weather, if the engine temperature drops close to the lower limit of the operating range (194°F or 90°C), the thermostat closes again.
Many modern cars use an electronically controlled valve called "coolant control valve" instead of a conventional thermostat. The coolant control valve works the same way only it's operated by the engine computer and is more precise.On some engines, the thermostat is mounted at the water pump inlet.
All thermostats operate in the same way and all the thermostat designs use a bypass passage, so that coolant is circulated through the water jackets by the water pump to ensure an even and complete warm-up of the engine. The thermostat is designed to open at a specific temperature, known as the rating of the thermostat, begin which may be stamped on it.
The two frequently used ratings are 358 K and 364 K.Most thermostats begin to open at their rated temperatures and they are fully at about 11 degrees higher (eg. at 375K)
Several designs have been used over the evolution of thermostats. The most widely used thermostat of the day is the wax-pellet type.
As the engine warms, heat swells an encapsulated wax-based plastic pellet located on the engine side of the thermostatic valve. This opens the thermostat through a mechanical link, which allows a portion of the coolant to flow to the radiator according to the engine cooling requirements needed to maintain a normal temperature. The remaining portion of the coolant continues to flow through the by-pass.
The coolant pump forces the coolant to flow. The thermostat restrictions cause the system pressure to rise, and the pressure lowers as the thermostat gradually opens, thereby increasing the coolant flow rate. Under extreme heating conditions of the engine like idling in traffic or moving up a long steep grade in hot weather, the thermostat opens wide allowing maximum coolant flow.
A small air bleed hole is usually placed in the thermostat body or valve or a notch cut into the mounting flange of the thermostat. This bleed hole or notch allows air to escape from the water jackets as they are filled with coolant. Bleeding the air out helps ensure that the cooling passages are filled during the coolant changes.
5 Thermostat failure symptoms and how to avoid them
1. High temperature readings
The main symptoms of a failing thermostat are related to engine overheating. It can be easily noticed because the temperature gauge in the vehicle will probably read unusually high. This can be caused by the valves being stuck in a closed position. As a result, the coolant will not be able to flow and overheating will damage the engine.
2. Erratic changes in temperature
Thermostat failure will commonly cause the whole cooling system functions erratically and fluctuates. Keeping an eye on the dashboard’s temperature gauge will allow you to realize if the needle spikes and drops. If this happens, it is probably due to temperature confusion caused by the failing thermostat. One of the symptoms of a bad thermostat related with the temperature is overcooling.
It’s the opposite of overheating: the engine never reaches operating temperature. This happens when a thermostat gets stuck open and it causes its fair share of issues as well.
3. Leaking coolant
The coolant helps to keep the engine functioning at the right temperature, and the lack or imbalance of the fluid can affect its performance. If the vehicle’s coolant leaks out of the thermostat’s housing or under the vehicle, there is a big chance that the air is getting into the system or that the coolant is escaping it. But keep in mind coolant can leak from different parts, don’t automatically assume it’s coming from the thermostat housing.
4. Increased fuel consumption
Both engine overheating and engine overcooling can largely increase exhaust emissions and damage fuel economy.
This happens because the vehicle is not able to reach its operating temperature. In this case, thermostat failure symptoms will most probably be translated into an increased fuel consumption and a resulting unexpected spike in monthly utility bills.
5. Unusual noises
Sounds coming from the engine, from the vibrator or from both could easily be symptoms of a failing thermostat. Gurling, knocking and rumbling sounds might be the result of boiling coolant caused by a stuck valve or by a worn-out thermostat.
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