Cooling system modifications that can increase fuel consumption

The cooling system is a key system of automobiles that controls the temperature of the engine and transmission. Modifying it can cause undesirable consequences on fuel economy, longevity, safety and so on of vehicle parts.
Last modified
11 Feb, 2024

The cooling system of a car is responsible for controlling the temperature of the engine and the transmission.

It achieves this by transferring heat from the engine or transmission to the coolant. The heat in the coolant is then exchanged to the air through the help of radiator, radiator fan and ambient air current.

Cooling system modifications

Some people find one or more excuses to modify the cooling system of their vehicle. Often times, these modifications are not beneficial or have negative impact on the system. Depending on the modification that is done, one of the negative impacts is reduced fuel economy.

Let's see some cooling system parts that when tampered with, can negatively affect fuel economy.

Cooling system modifications that negatively impact fuel economy

1. Thermostat removal

The thermostat helps to bring the engine to operating temperature quickly by preventing coolant circulation at cold start. Since heat is not initially transfered away from the engine, it attains closed loop and operating temperature on time which helps to conserve fuel. In open loop state, a lot of fuel is dumped into the engine to make it attain operating temperature on time. Generally, it is a bad idea to remove thermostat.

2. Fan speed control bypass

This is practically direct radiator cooling fan connection to a power source. It can be done through connection of the fan's terminals directly to power source or through bypass of cooling fan relay or cooling fan control unit. 

This has negative effects and increases the load on the engine as the fan runs at maximum speed and draws a lot of power. 

Again, most fan control circuits use pulse width modulation, a technology that helps to reduce the power that is consumed by electrical loads. A direct power connection causes more power and fuel consumption.

3. Mechanical fan clutch bypass

Some old model vehicles use mechanical fan clutch to vary the speed of radiator fan. The clutch doesn't last forever and some car users or mechanics just weld the clutch to the fan causing the fan to run at the same speed with the engine. That is a way they bypass the fan clutch. Sometimes, they do this to mask overheating even when the clutch is good and not the cause of overheating. This makes the engine to overcool and consequently consume more fuel.


4. Installation of bigger radiator

Bigger radiator like dual core radiators cannot directly increase fuel consumption but many times when people make the modification of installing a bigger radiator, they also remove thermostat.

5. Coolant temperature sensor removal

The CTS is a negative temperature coefficient sensor that sends signal to the ECU based on the temperature of the coolant in the cooling system. With the help of this signal, the ECU is able to know when the electronic fuel injection system should be put into closed loop. If the CTS is disconnected, the system will be in open loop most of the time, will dump fuel into the engine which will cause poor fuel economy.