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.