MK5 Golf GTI

All Things Mk5 => Modifications & Technical Area => Technical Workshop => Topic started by: W3THS on October 08, 2011, 09:30:28 am

Title: Diagnosing a faulty thermostat
Post by: W3THS on October 08, 2011, 09:30:28 am: Hi,

I'm after some advice on whether my thermostat is stuck open. My car seems to take ages to warm up (it just gets over 50 after an 8 mile journey) and ive noticed that the cooling fans don't seem to kick in. Is there anyway i can find out if a) the fans are knackerd b) the thermostat is knackerd.

Thanks
Title: Re: Diagnosing a faulty thermostat
Post by: john87 on October 14, 2011, 12:12:31 pm: Hi,

definitely sounds like the thermostat - my friends' Bravo (petrol) takes ages to warm up, and once on the motorway, the temp often drops back down to below 1/4 of the way up the scale :confused:
Title: Re: Diagnosing a faulty thermostat
Post by: bacillus on October 15, 2011, 03:56:56 pm: I think a vcds scan would help identify if your thermostat was faulty.
Title: Re: Diagnosing a faulty thermostat
Post by: W3THS on October 18, 2011, 05:13:33 pm: i've done a scan but nothing to do with the thermostat shows up, is there any other way of checking through vagcom? maybe measuring certain blocks?
Title: Re: Diagnosing a faulty thermostat
Post by: Pullafacial on December 07, 2011, 02:27:10 pm: Hi, did you get this sorted? Got the same problem with mine

Steve
Title: Re: Diagnosing a faulty thermostat
Post by: ktlstar on December 07, 2011, 04:07:45 pm: Could you not just take it out yourself if its easy enough ? then just stick it in boiling water to see if its opening,
Title: Re: Diagnosing a faulty thermostat
Post by: Phil Miller on December 07, 2011, 07:45:18 pm: A failed thermostat will not give a code on vcds you will need to remove it and test, for the sake of £20 I'd just replace it with one from TPS mate
Title: Re: Diagnosing a faulty thermostat
Post by: Teutonic_Tamer on February 06, 2012, 10:05:25 pm: Quote from: bacillus on October 15, 2011, 03:56:56 pm
I think a vcds scan would help identify if your thermostat was faulty.

Thermostat is NOT map controlled - only the fans are.

Thermostat operation can be easily diagnosed the old skool way of holding the top hose and smaller heater hoses from a cold start. With a correctly functioning stat, the heater hoses will warm up first, usually quite quickly - but progressively; whereas the top hose will stay cold for ages, then suddenly get feckin hot. If the stat has stuck open, the top hose will heat up slowly and progressively the same time as the heater hoses.

One other thing which no-one has mentioned is anti-freeze strength - too much anti-freeze (ie, more than 50% strength) can dramatically affect the coolant, and therefore the heater.