<!-- from fixya rte -->What are thermostat symptoms - 318 BMW Cars & Trucks

Yes, that could easily be a thermostat going bad. Listen for you water pump as well. Symptom of that going bad is a high pitch squeal upon start up.

How to Change a Car Thermostat : How to Diagnose Car ...

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Learn how to diagnose thermostat symptoms for car thermostatrepair ... i think my thermostat is failed open. i did the obd1 check with a paper ...

How to change water pump on 2L FWD Transit ' Do Your ...

white smoke out the tailpipe and the smell of anti-freeze in the exhaust gas. an engine that over heats either only at highway speeds or town driving, when all other things like, rad cooling fan working properly, thermostat is working properly, no external coolant leaks. the spark plugs may show signs of coolant on them. just some things that are indicators.

If you have no heat in your vehicle then it is probably the heater core which is just a small radiator that sits behind the glove box. The thermostat itself is probably located where your top radiator hose connects to your engine. It is an easy and cheap fix, just pull the hose away after undoing the clamp and you should see it. If it is not there, then it will be in the bottom hose. Hope that helps you out.

thermostat might be stuck shut, most likely reason for those symptoms

What are you going by to say it's overheating , temp gauge ? Have you test to see what the actual temp. is > Hook - up a scan tool ,what's the PCM - engine computer seeing for engine temp. ? 223 degress the PCM should turn on the cooling fan . You could buy a Non-Contact Infrared Thermometer With Laser Targeting at harbor freight ! Radiator very hot ????? What is the right temp .
Non Contact Infrared Thermometer With Laser Targeting

Could be a bad temp gauge . Is the coolant surging inside the cooling system ? Does it have a radiator cap ? Have you replaced it ?

When your temperature gauge reaches "H' it may too late to prevent a major breakdown. Knowing the symptoms of an overheated car and how they occur may be the difference between being inconvenienced and incapacitated.
Identification:---Other than a low oil level or low oil pressure light, there is not a more significant part of a car's instrumentation than a rising temperature gauge or a glowing "Hot" light. These lights are really the only confirmation a driver has that his car is really overheating. It is the identification of the symptoms of an overheating car that enable the motorist to avert a badly damaged engine. Overheating is always a traumatic event for a car's engine, which makes the early identification of the symptom an important addition to the informed motorist's tool kit.
Stuck Thermostat:--The car's thermostat is a valve that controls coolant flow from the engine block to the radiator. When the engine is cold the thermostat remains closed so that the coolant can reach operating temperature quicker and also provide heat to the passenger's compartment. The thermostat has a spring on it that moves depending on coolant temperature causing the thermostat to open. Sometimes the thermostat fails to open thus restricting coolant flow to the radiator where it would be cooled down. This condition is often the cause of overheating. The symptoms of this cause would be a rising temperature gauge and possibly the loss of heat inside the car.
Restricted Radiator:---A car's radiator will have thousands of gallons of coolant passing through in its lifetime. Along with the coolant comes particulate matter in the form of corrosion breaking loose from various parts of the car's cooling system. These contaminates collect in the tubes of the radiator reducing its efficiency. Extensive "plugging" in the radiator will cause the car to overheat. The symptom of this condition would be a rising temperature gauge which goes up when you accelerate.
Coolant Loss:--A car's cooling system is a closed loop system. You are not supposed to lose coolant. Sufficient coolant loss will cause the engine to run hot because engine is heating less coolant to higher temperatures. The symptom of overheating induced by coolant loss would be a pool of coolant on the pavement when the leak is external. Steam under the hood as the lost coolant hits hot parts of the engine, or a rising temperature gauge in the case of a undetectable engine related leak. Of course, the gauge would also go up if the leaks were not detected. Deteriorated Water Pump:--Cars use a belt driven pump to push the water and coolant mixture through the cooling system. This part is called the water pump. Rarely the impeller that draws the coolant through the pump will rust away making it impossible to push any through the system. If this occurs the temperature gauge will climb and coolant will boil over in the radiator. Inoperable Fan:----Most cooling fans are electrically driven. Some are driven by fan belts. If a belt breaks or the electric supply to the fan is interrupted overheating may result. Electric fans are tuned on thermostatically when needed. When the car runs at idle for extended periods or the weather is extremely hot, a failed fan will cause overheating otherwise it serves as a standby assist to the rest of the cooling system. In stress conditions an inoperable fan will cause the temperature gauge to rise. This will help. Thanks please keep updated.please please do rate the solution positively .thank you for using fixya

There are two primary symptoms of a faulty thermostat (assuming you mean the coolant thermostat in the engine not the A/C Heater Thermostat).  The thermostat can fail in basically two ways:
1)  Stuck open - Engine runs colder, heater takes forever to heat up. 2)  Stuck closed - Engine runs very hot, then will suddenly drop in temperature, then run very hot again.  Or engine overheats constantly.  When the engine is hot, feel the upper radiator hose.  If it is not hot, you can bet the thermostat is stuck closed.  If it is hot, the thermostat may not be stuck close, but not opening at the proper temperature.
Stuck open is annoying, but not dangerous.  Stuck close is dangerous and can cause overheating-related damage to your engine.
If you are handy, you can replace it yourself.  Otherwise it is an easy job for a mechanic.

It does sound like the thermostat. The sensor does not control the thermostat in any way, it only reads the temperature of the coolant. Your symptoms are classic of a thermostat that is stuck open or partially open. Take it back and tell them what is going on and have them show you that the thermostat is fine.

2.4L 4cylinder

2.5L 6cylinder