Effects of engine overcooling
1. The engine will run rich and consume more fuel because the ECM will react to the low temperature signal from temperature sensor by dumping more fuel to allow the engine attain closed loop and operating temperature. This can lead to overfueling that causes bore wash which in turn causes rapid engine wear.
2. Internal parts like piston rings will wear out easily as there won't be sufficient heat that causes expansion which allows sufficient clearance between the piston ring and the cylinder wall.
3. Engine oil becomes contaminated as the heat of the engine is not adequate to burn off moisture and fuel in the oil.
4. The overall efficiency of the engine is reduced as engines are most efficient at their operating temperatures.
5. The engine oil does not thin out to the viscosity that it should be at operating temperature. This also increases fuel consumption as the engine works harder to overcome the weight of the oil. The oil might also not thin out enough to lubricate tight spaces in the engine.
6. Carbon and sludge build up is another effect of engine that does not attain operating temperature.
7. An engine that is overcooled has higher emissions level.
How to fix an engine that is running too cold
1. Replace a faulty thermostat with a good one.
2. Fix cooling fan system to work in the factory operating mode.
3. Replace a faulty temperature sensor with a good one.
4. Replace a faulty ECU with a good one.
5. Fix bad wires, connectors and plugs.