Typically the coolant will not stay in the engine long enough to get hot so you will get cold air from the heater. Engine parts are shaped to fit perfectly when they expand to normal operating temperature. 99 percent of engine wear takes place in the first five to ten minutes of driving after starting a cold engine. You will be holding the engine temperature in that range where wear takes place so the engine's life will be greatly reduced. Also, one of the jobs of engine oil is to carry carbon and other harmful products to the oil filter. The bad stuff won't disperse into the oil to be carried away. That also decreases engine life.
In rare instances the engine can overheat when there's no thermostat. The hot coolant doesn't stay in the engine long enough to give up its heat.
You aren't solving any problem by leaving the thermostat out. Also, the Engine Computer goes into "closed loop" when the engine is above a certain temperature. That is when it adds the oxygen sensors' readings to the fuel metering calculations and fine tunes them for best fuel mileage and lowest emissions. If the engine doesn't get to a high enough temperature, it will be like driving an older car with the choke stuck on.
If this goes on long enough, it's possible to set a diagnostic fault code for "Engine running cold too long". On some models that will turn on the Check Engine light. That can turn into a big problem because if a totally different, minor problem is detected, you won't know it because the light is already on. Many minor problems can turn into real expensive problems if they're ignored.
Monday, January 25th, 2016 AT 3:57 PM