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  1. #1
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    A little thermostat help? 01' A3, AVU engine.

    Hey, have searched and read up as much as I can but still can't find an answer to my question. If anyone can help out any with the following problem would be much appreciated.

    I have a 01' A3 facelift, 1.6L AVU engine. When I first got the car, the fans would come on seconds after the car was started and remain on after the car was turned off and continue to run untill the battery died. After some forum searching it looked as though my thermostat could be the problem, so I replaced that and why I was at it put in a new temp sensor as well. Put it back together, fans now don't come on, car will heat up to 90deg, fans still don't come on and she continues to heat up. Heater works extremely well, coolant topped up. I have noticed that even when very hot 90+ on the guage, the bottom radiator hose is dead cold along with the radiator, all top hoses very hot. I have checked the radiator to make sure it's not blocked, it's not.. water flows nicely through when checked with the hose. I don't believe the water pump is my problem as it was replaced 5,000km ago and water flows nicely back to the coolant reservoir at any rpm, and my heater works well.

    Next I thought could my brand new thermostat be the problem (thermostat is the complete housing type with a electronic connection), I have put it in boiling water on the stove for 5minutes and noticed no change .. still completely closed. Did some more forum searching, but am now confused as to whether this thermostat would ever open with just boiling water as I have read it is electronically controlled .. and again read different info telling me the electronic part of the thermostat is just to tell the ECU how hot the car is and to turn on / off the fans..

    As such i'm kinda stuck with what to do next, buy another thermostat or do i have an ECU problem? It hasn't thrown any CEL.

    Sorry for the big first post chasing help , but hopefully this thread will help others in the future.

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  3. #2
    mark_S3's Avatar
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    Maybe not the cause, but could be a air blockage in the system. Did you bleed the system after installing the thermostat?

    Normally if there is a air blockage in the system, the fan wont kick in.
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    I tried to bleed it the best I could, pulled the bottom radiator hose off from the thermostat a touch to let any air out till coolant came out, did the same on the top radiator hose, removed the temp sensor to bleed any air out, and squeezed all lines till i had no bubbles coming into the reservoir just the coolant level going up and down as i squeeze. How are the fans controlled? Via the thermostat, or temp sensor?

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    mark_S3's Avatar
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    Yer the fans are controlled by the thermostat. Once water is too hot the thermostat tells the fans to kick in.

    Ive always been told to bleed the system like this:
    Top up system. Leave cap off on the expansion tank. Turn engine on. Put heaters on full blow and heat. Leave engine on idle, and watch coolant level. Top up if necessary. Keep pumping top hose if necessary aswell. And just til fans kick in. Usually it happens within 10mins. Always done the trick for me on different motors.

    I'm sure everyone has different ways, but thats how ive been told is the correct way.
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    Quote Originally Posted by mark_S3 View Post
    Yer the fans are controlled by the thermostat. Once water is too hot the thermostat tells the fans to kick in.

    Ive always been told to bleed the system like this:
    Top up system. Leave cap off on the expansion tank. Turn engine on. Put heaters on full blow and heat. Leave engine on idle, and watch coolant level. Top up if necessary. Keep pumping top hose if necessary aswell. And just til fans kick in. Usually it happens within 10mins. Always done the trick for me on different motors.

    I'm sure everyone has different ways, but thats how ive been told is the correct way.
    I'm pretty sure it is bled properly, just the thermostat will not open and no fans will go on no matter how how it gets.. Starting to think I have a dud brand new thermostat? Anyone else have any ideas to try before ordering another thermostat? (Gets expensive unfortunately, ordering from UK when im in Australia)

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    A little thermostat help? 01' A3, AVU engine.

    Thermostat doesn't control when the fans switch on. Only when full circulation as allowed to the radiator.

    The fans are control by a temperature sensor normally located in the radiator. When a certain temperature is reached this switch tells the ecu to activate the fans.
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    Quote Originally Posted by Lewis583 View Post
    Thermostat doesn't control when the fans switch on. Only when full circulation as allowed to the radiator.

    The fans are control by a temperature sensor normally located in the radiator. When a certain temperature is reached this switch tells the ecu to activate the fans.
    Ok thanks for the info, would you know though why the fans would constantly be on before i replaced the thermostat? And when the thermostat is unplugged the fans run constantly even when the car is cold? New thermostat plugged in fans wont go at all

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    A little thermostat help? 01' A3, AVU engine.

    Do you mean temp sensor when you say thermostat?

    The thermostat is mechanical not electrical. As I said earlier there should be 2 coolant temp sensors on the engine. One for telling ecu and one for controlling the fan.
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    Quote Originally Posted by Lewis583 View Post
    Do you mean temp sensor when you say thermostat?

    The thermostat is mechanical not electrical. As I said earlier there should be 2 coolant temp sensors on the engine. One for telling ecu and one for controlling the fan.
    The thermostat has a electrical plug connected to it, it is the type with the thermostat built into the housing with a electrical connector on the housing. There is also a "green" coolant temp sensor, have not looked on the radiator for another temp sensor

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    vfr800's Avatar
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    Thermostat looks like this:



    Have you got Climate Control? If so, you can get it to tell you what the car thinks the coolant temperature is.
    Follow this guide Climate Control Codes... - AudiForums.com
    For most people with an 8L the address (code) 49c gives the coolant temp.

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    Quote Originally Posted by vfr800 View Post
    Thermostat looks like this:

    not on the 1.6 it doesn't. The 1.6 uses a map controlled thermostat which looks like this: http://www.anto.ru/photo/070904-golf...e/_MG_1840.jpg. OP, it does sound like your thermostat is not opening properly.
    Last edited by kevandalice; 15th November 2012 at 22:04.

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    Quote Originally Posted by kevandalice View Post
    not on the 1.6 it doesn't. The 1.6 uses a map controlled thermostat which looks like this: www.anto.ru/photo/070904-golf/content/bin/images/large/_MG_1840.jpg. OP, it does sound like your thermostat is not opening properly.
    Yip thats the thermostat I have, do you know if theres anyway to test this thermostat? Otherwise i'll get my hands on a genuine this time

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    90 on the temperature dial on the dash is the correct running temperature it is not "too hot" - I have several photos going back to when my car was new which prove that.
    My car currently reads about 72 which is caused by a faulty thermostat.

 

 

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