Possible thermostat going bad?

[Gwill21]

Hi all,
Just noticed on a drive last night my temp gauge seems to be fluctuating a little whilst driving, it would drop to about 80-85 odd and then rise back up to 90 again, sound like a knackered thermostat or is this normal behaviour for the mk5 gti's?
Any responses would be appreciated!

[lukemk5gti]

Your main thermostat is gone.

A manual gearbox has a main and an inline thermostat. A DSG has a third inline thermostat.

The symptoms you have are connected to the main one which needs a total front end removal for replacement of the thermostat.

Expect to pay anywhere from £250 - £500 from independent to main dealer.

It's worth replacing your inline while you're at it.

[ReflexRob]

Just had mine done as I had temperature fluctuation. I also had the valves cleaned whilst the front end was stripped down as it reduces that cost by about 100 quid.

Where are you based?

[Gwill21]

Just had mine done as I had temperature fluctuation. I also had the valves cleaned whilst the front end was stripped down as it reduces that cost by about 100 quid.

Where are you based?

Great more money out the pocket then!! 
Based in the midlands pal, northamptonshire

[ReflexRob]

Tell me about it - I had £1100 bill for the thermostat, valve clean, cam chain and tensioner, dv replacement etc.

If you are prepared to travel then Dialynx in Swindon are excellent and not too pricey. They reckoned about £200 labour for the thermostat.

[Gwill21]

An additional note, I did just have my cambelt +water pump changed on Monday, would that affect it in any way or does it not make a difference? As I just did a small drive today and it got to 90 and sat there? Granted it wasn't a very long drive compared to before

[lukemk5gti]

An additional note, I did just have my cambelt +water pump changed on Monday, would that affect it in any way or does it not make a difference? As I just did a small drive today and it got to 90 and sat there? Granted it wasn't a very long drive compared to before

That won't affect it. If the sensor has only started to fail it will intermittently reach 90.

If money is tight and you're not OCD about the needle watching then you can leave it for a while, it won't have any significant impact on your car other than a minimal drop in MPG.

[Gwill21]

Well it's good to know it doesn't need doing like asap, yeah well leaving it for a couple months would be handy so I don't have to put it on my credit card!
Thanks for all the responses though, greatly appreciated!

[ReflexRob]

I was driving mine for 18 months after I bought it with the needle mostly sitting at 75. Didn't appear to do any harm or even affect MPG but no doubt the extra fuel wouldn't be ideal for sensors.....

[ducman77]

Here's a bit of a DIY buddy if you're into that kind of thing

Total cost;
€50 for main stat
€60 for both inline stats (you'll only need one if yours is a manual car)
€20 for 3ltrs of VW G13 coolant (50:50 mix with water)

Just completed this job last week. It is a pain in the balls. But very doable.

I have bruises all up and down my forearms from trying to do all the required work in the tiny space available 

Undertray off...
Boost pipe off...
Drain coolant from where the lower radiator hose meets the electric water pump under the car...
Auxiliary belt off...
Tensioner out...(optional)
Prize the alternator out with a pry bar....
There are three pipes attached to the thermostat...
The two rubber ones on top and bottom are simple enough to remove...
The metal one coming out of the front of the stat requires you to remove the two small triple square bolts holding it to the front of the engine block so that you can then wiggle it enough to get it off....
Remove the main stat...
Replace with new stat....

TOP TIP for reassembly;
Push the metal "bushes" on the alternator out a bit before you try and refit it. Otherwise it's way too tight a fit and you'll never get it back in. Don't worry the bolts will pull the bushes back into their correct position as you tighten them up.

Now enjoy your car behaving like a normal car because it actually has a working thermostat. Hallelujah 

I found this video quite helpful.....


Hope all that helps.
Regards,
Dave

[ducman77]

Sorry - here's the video link....

[pudding]

As above, you don't need to remove the front end at all.

What does the inline one actually do?  I only replaced the main one on mine.

[ducman77]

I think the inline stats keep the cooling system compartmentalised until such time as the engine block itself is sufficiently warm.

Once warm enough the inline stats open and allow water to go to the heater core and DSG gearbox.

If your inline stats are stuck open the car will take longer to heat up.

If your main stat is gone not only will the car take longer to heat up but the temperature will actually drop from 90 (ish) to 70 (ish) when you're driving on the motorway.

I'm not sure there was anything wrong with my inline stats but I changed them anyway cos they're pretty cheap and I just fancied fitting all new gubbins.

That's my understanding of it. But I'm open to correction??

[Gwill21]

Thank you for all the very detailed replies! I think mine must be only starting to fail as the car still tends to warm up after a couple of miles and the fluctuation of temperature only went between a minimum of 80 and max of 90!
I'll keep an eye on it and once I've got the cash together I'll get it sorted!
Thanks again!

[pudding]

I think the inline stats keep the cooling system compartmentalised until such time as the engine block itself is sufficiently warm.

Once warm enough the inline stats open and allow water to go to the heater core and DSG gearbox.

If your inline stats are stuck open the car will take longer to heat up.

If your main stat is gone not only will the car take longer to heat up but the temperature will actually drop from 90 (ish) to 70 (ish) when you're driving on the motorway.

I'm not sure there was anything wrong with my inline stats but I changed them anyway cos they're pretty cheap and I just fancied fitting all new gubbins.

That's my understanding of it. But I'm open to correction??

Cheers mate, makes sense.  I think I'll change my inline one as well because it still seems to take ages to warm up when cold!