Audi a4 s line 2006 silencer and engine overheating, coils changed to no use, thermostat between cold and hot..

You need to diagnose to find out what is CAUSING the coolant error. I cannot tell you what is causing it without diagnosis being performed and although many uneducated peope may try to "guess", neither can they tell you for with any certainty. Diagnosis begins with many questions that must be answered:

> Is the engine running too hot?
> Is the engine running too cold?
> Is there a malfunction in the engine coolant temperature sensor circuits?
> Is the data from the sensor within its designed parameters?
> Is the sensor providing the correct temperature reading to the computer? Or if not, is the reading too high or too low?
> Is the thermostat opening at the correct temperature?
> Etc. Etc..

First time you might check the thermostat operating.

Heed of antifreeze coolant temperature!!!

The thermostat location for a 2000 Audi A4 1.9 TDI is on back of the alternator at the bottom side of the bracket.

IMPORTANT NOTE: It is NOT necessary to replace the alternator if you want to change the thermostat !!!

Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 044121113, in german - "Kuehlregle" (Price around $25):


Important note: Always replace the thermostat round seal, position 7 in the above picture.

Check the radiator and the cooling fan. open the hood as the engine temperature rises does the fan come on. if not that the problem, Also do this As the car is warming up(from a cold start) near operating temperature, turn off the car, watch out for the fan, engine of key in your pocket fell the radiator is there any hot or cold spot? if there is the radiator is plugged. Also if the radiator isnt plugged new doesnt mean it works, the water pump itself can be faulty. and dont forget the most important device the Thermostat you did timing belt waterpump they should of done thermostat.

REPLACE THERMOSTAT.MAKE SURE COOLANT SUPPLY PIPE OR COOLANT RETURN PIPE NOT STOPPED UP AND YOU HAVE ENOUGH COOLANT IN THE SYSTEM.REPLACE THERMOSTAT.CRANK ENGINE UP AND LET IDLE UNTIL WARM UP KEEP EYES ON TEMPERATURE GAUGE. WHEN ENGINE THERMOSTAT OPEN COOLANT HOSE SHOULD BE HOT.IF NOT TURN OFF ENGINE.USE LARGE RAG WAIT A WHILE BEFORE REMOVING RADIATOR CAP CHECK TO SEE IF COOLANT LEVEL DROPPING IF SO ADD MORE COOLANT.CRANK ENGINE UP UNTIL THERMOSTAT OPENS UP.HOSE WILL GET HOT.IF STILL COLD CHECK COOLANT LEVEL.ONCE YOU AIR OUT COOLANT SYSTEM RADIATOR HOSES WILL GET HOT SO YOU WILL GET HEAT.IF COOLANT LOW YOU WONT GET NO HEAT.

Sounds like something is wrong with your climate control

Alot of time you have to bleed the cooling system after changing a thermostat it gets an air pocket in it look for a bleeder valve near or on the thermastat housing if so bleed it to get the air out.check the radiator and make sure its full because if you filled it up after changing the thermastat once the thermastat opened after the engine ran awhile well the cooling system needs refilled.

The thermostat is faulty. Change the thermostat.

sounds like the thermostat is not functioning correctly? either that or not in at all? thus making the water which would normally warm up quickly, warm up extremely slowly and on really cold days not at all? with a 2.6 engine your car shoudl warm up in record time?

My 2002 Audi A4 doesn't produce the hot air, It's an Auto computer control temperature system. I took my car to the local mechanic (gas station), he said that the water pump and the timing belt need to be replaced.

The heating system normally produces by the engine, then normally the "thermostat' is causing the issue, but the temperature gauge doesn't indicate the overheat.

Any idea what's cause this problem?

Try replacing the engine temp sensor. Temp sensor is telling ECU the engine is hot when its is actually cold. After the 6th attempt there is enough fuel in the cylinders to create a ritch mixture, then it goes.

TL