About 3 months ago I replaced the entire coolant (and thoroughly cleaned the whole cooling system). Immediately after I noticed that on cold starts the temp needle wouldn't get to 90 degrees as fast as it did before.

Now, since the mornings are colder (13-15 degrees celsius) I find that it takes about 8-9km for the needle to get to 90, given also that until it gets there I never go past 2500rpm and drive very gently and it's mainly on motorway (kind of constant speed).

Also, when it's chilly outside (like nights) if i'm in gear and lift off the throttle, engine-braking for a while (e.g. I see a truck in the distance then I just let off the gas and "float" towards it, no brake pedal at all) or going down hills i see the temp needle going down from 90 as much as two units (lines), although usually it only goes down to the nearest line.

Is this whole behavior normal? Should I change the thermostat?

offtopic: anyone else get kind of a big difference in power when it's cold outside? I mean, even though I have a twintercooler, the difference in how it pulls between 31 celsius and 15 celsius is quite big!

About 3 months ago I replaced the entire coolant (and thoroughly cleaned the whole cooling system). Immediately after I noticed that on cold starts the temp needle wouldn't get to 90 degrees as fast as it did before.

Now, since the mornings are colder (13-15 degrees celsius) I find that it takes about 8-9km for the needle to get to 90, given also that until it gets there I never go past 2500rpm and drive very gently and it's mainly on motorway (kind of constant speed).

Also, when it's chilly outside (like nights) if i'm in gear and lift off the throttle, engine-braking for a while (e.g. I see a truck in the distance then I just let off the gas and "float" towards it, no brake pedal at all) or going down hills i see the temp needle going down from 90 as much as two units (lines), although usually it only goes down to the nearest line.

Is this whole behavior normal? Should I change the thermostat?

offtopic: anyone else get kind of a big difference in power when it's cold outside? I mean, even though I have a twintercooler, the difference in how it pulls between 31 celsius and 15 celsius is quite big!

dont know about the first bit but the second bit made me chuckle

do you know how your engine works?? have a read remebering when air is cold its more dense offcoruse you will have more power when cold outside best time to drive is when its foggy:eek: why do you think we all go to such lenghts to lower the air temp going into the engine i.e front mounts water methanol cryogen etc etc we wouldnt do that if the car ran faster when warm would we lol:rofl:

Come on westalic, not everyone is a whiz with engines.

About 3 months ago I replaced the entire coolant (and thoroughly cleaned the whole cooling system). Immediately after I noticed that on cold starts the temp needle wouldn't get to 90 degrees as fast as it did before.

Now, since the mornings are colder (13-15 degrees celsius) I find that it takes about 8-9km for the needle to get to 90, given also that until it gets there I never go past 2500rpm and drive very gently and it's mainly on motorway (kind of constant speed).

Also, when it's chilly outside (like nights) if i'm in gear and lift off the throttle, engine-braking for a while (e.g. I see a truck in the distance then I just let off the gas and "float" towards it, no brake pedal at all) or going down hills i see the temp needle going down from 90 as much as two units (lines), although usually it only goes down to the nearest line.

Is this whole behavior normal? Should I change the thermostat?

offtopic: anyone else get kind of a big difference in power when it's cold outside? I mean, even though I have a twintercooler, the difference in how it pulls between 31 celsius and 15 celsius is quite big!

I'd be tempted to change the stat. I wouldn't expect the temp to drop once up to 90, and it seems to be warming up slowly- that's more normal for a TDI.

:iagree: - this certainly reads like the car is over-cooling, and a stuck open stat is the most likely cause of that.

:iagree: - this certainly reads like the car is over-cooling, and a stuck open stat is the most likely cause of that.

Mines doing the same :confused: How much for a new stat?? and are they easy to fit??

dont know about the first bit but the second bit made me chuckle

do you know how your engine works?? have a read remebering when air is cold its more dense offcoruse you will have more power when cold outside best time to drive is when its foggy:eek: why do you think we all go to such lenghts to lower the air temp going into the engine i.e front mounts water methanol cryogen etc etc we wouldnt do that if the car ran faster when warm would we lol:rofl:

What i was asking was if there was a big difference. Of course there is a difference, but, at least on my car, there's a big difference, like some extra 25 hp or something

Regarding the thermostat, it's kind of a pita to fit, but that's what mechanics are for, right?

if you have to change the stat then have a look at the cooler ones on AwesomeGTI Awesome > Neuspeed 1.8T 180 Degree Thermostat they also do a matching fan sensor Awesome > Neuspeed 180 Degree 3 Pole Fan Switch drops the running temp by 15F

The engine is designed to run at 90, why would you want it running cooler ?

:iagree:

Carnot heat engine - Wikipedia, the free encyclopedia

I'd say you'd only want a "colder" 'stat and thermoswitch if you're having persistent problems with overheating, for instance if you're running a heavily-modified engine...

3rded.

3rded.

4thd. While you might want cold air going in (so it's denser), you want the engine to be as close as possible to it's design 'warmed-up' temperature.

The engine is designed to run at 90, why would you want it running cooler ?

Absolutely. With ECU controlled engines, you don't want to run the engine cold as it screws up the engine management. Even with a heavily modified engine, you would want to increase the cooling capacity rather than try to reduce the operating temperature. That would be a last resort.

Yea, I agree. But if you go to the track a lot maybe then it would be a smart move? On ordinary and even with spirited driving on public roads I don't think there's any point in a cooler engine

All this is missing the point, though. You want the engine to run as hot as it can without the risk of damage (i.e. at 90 degrees) in the interests of efficiency, as described by Carnot's theorem. Therefore, only if you were having persistent problems with overheating would you want to look at altering the setpoints of the thermostat and thermoswitch, although as has been quite rightly pointed out, if you're overheating all the time, having the coolant circuit running at lower temperature won't need much help because unless you do something about the size of the radiator and/or the rating of the waterpump, you'll still end up overheating, just a little bit longer after starting the car...

Back to the original point, it sounds like the OP's thermostat is indeed stuck open (the symptoms are just like when the 'stat body went on my wife's car - both times!), so it and/or the housing - depending on the design - need to be replaced. With OEM or equivalent parts!