I own an Audi A3 2001 8L1. When engine gets to operating temperature it sometimes starts to overheat. I touched the radiator after driving the car for some time and it was completely cold to the touch but the engine was at operating temperature.

I've changed the thermostat a few months ago and now I'm thinking that I either installed a broken one or installed it the wrong way, but from looking at images online I doubt that is the case.

I'v also noticed some people say it could be the heater core clogged up but this is not the case here as it is blowing hot air when set to maximum.

I've only recently noticed this as the past few months were very cold so I never had an overheating issue.

Any ideas?

1 Answer 1


Quick answer for engine overheating/cold radiator would be:

a) Check there is coolant in the system: refill as needed and check for leaks. Remember to purge air bubbles: my way is that as I add coolant I squeeze the hoses attached to the engine, like a hand rubber pump, then start the engine without radiator cap, for some seconds, then redo.

b) Check thermostat: an easy way is to remove the thermostat completely and run the engine without it for a test. A way to check the thermostat is to heat water and immerse the thermostat hanged with some wires, if water is hot enough (varies for thermostats but would be between 80C to 90C) the thermostat should "click", i.e., open. NOTE: some engine designs requires the thermostat to be placed in its correct position, otherwise coolant won't flow as designed/needed.

c) Check water pump: be sure engine has coolant, start engine and slowly release the "out" hose from the engine, commonly at the engine's head. Or slowly release the hose to the radiator. You should see water coming out with some pressure. Otherwise, remove water pump and check if it is sound.

d) Check water coming out from engine: the engine block/engine head could be severely stuck. Add coolant, start engine, release "out" hose. Coolant should flow out with pressure.

e) Check "in" and "out" hoses in radiator: release one first, check, then the other. Coolant should flow freely, otherwise radiator could be clogged.

Resuming what to blame:

No coolant, bad thermostat, bad water pump, clogged engine block/engine head (it was my latest ordeal...totally blocked with soil), clogged radiator (was my previous ordeal, when acquired this car...tons of gasketmaker silicon gunk).


When starting the engine for the procedures I said above, always do with cold engine! Don't scald yourself. Starting the engine for a few seconds, cold, to check this stuff won't be enough time to heat it that much, and if it does, just let is cool down.


The correct way to install the thermostat into its flange:

enter image description here

  • Thanks @Aram very helpful. a) is checked. I will get on b) tomorrow morning, go for a long drive and let you know how it went.
    – erikvimz
    Commented Mar 11, 2017 at 16:46
  • 1
    Some people discourages starting the engine without thermostat because it won't reach the operating temperature at a given designed time, so oil will be more viscous for more time, not reaching some zones, etc. While that's true, for a quick test it will be fine. Otherwise point B could be done with the engine lukewarm..."touchable". I live in a tropical island: everybody removes the thermostats here :) Commented Mar 11, 2017 at 16:56
  • @AramAlvarez - Some cooling system designs require there be a thermostat in it or the coolant flow will not happen correctly, causing more issues than solving. My 94 Camaro Z28 with the LT1 engine was like this. Commented Mar 11, 2017 at 17:23
  • @Paulster2 - Exactly...and edited the question to reflect your comment. Commented Mar 11, 2017 at 18:52
  • @AramAlvarez I've now removed the thermostat and water is now flowing like crazy, the radiator is getting sort of hot but never hot enough to trigger the fans which is normal I guess considering current temperatures are around 10ºC... For now I will drive without the thermostat so the water will circulate and hopefully cleanup the mess inside, after a week I'll reinstall a working thermostat and let you know how it went, thanks for now.
    – erikvimz
    Commented Mar 12, 2017 at 14:21

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