MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: Gwill21 on November 09, 2016, 10:06:56 am

Title: Possible thermostat going bad?
Post by: Gwill21 on November 09, 2016, 10:06:56 am
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!
Title: Re: Possible thermostat going bad?
Post by: lukemk5gti on November 09, 2016, 12:05:01 pm
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.
Title: Re: Possible thermostat going bad?
Post by: ReflexRob on November 09, 2016, 12:13:24 pm
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?
Title: Re: Possible thermostat going bad?
Post by: Gwill21 on November 09, 2016, 12:16:12 pm
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!!  :doh:
Based in the midlands pal, northamptonshire
Title: Re: Possible thermostat going bad?
Post by: ReflexRob on November 09, 2016, 12:33:37 pm
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.
Title: Re: Possible thermostat going bad?
Post by: Gwill21 on November 09, 2016, 12:44:38 pm
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
Title: Re: Possible thermostat going bad?
Post by: lukemk5gti on November 09, 2016, 12:50:09 pm
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.
Title: Re: Possible thermostat going bad?
Post by: Gwill21 on November 09, 2016, 12:58:20 pm
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!
Title: Re: Possible thermostat going bad?
Post by: ReflexRob on November 09, 2016, 01:53:01 pm
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.....
Title: Re: Possible thermostat going bad?
Post by: ducman77 on November 09, 2016, 02:16:27 pm
Here's a bit of a DIY buddy if you're into that kind of thing :rolleye:

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  :laugh:

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  :smiley: :happy2: :rolleye:

I found this video quite helpful.....


Hope all that helps.
Regards,
Dave
Title: Re: Possible thermostat going bad?
Post by: ducman77 on November 09, 2016, 02:19:44 pm
Sorry - here's the video link....
Title: Re: Possible thermostat going bad?
Post by: pudding on November 09, 2016, 02:33:35 pm
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.
Title: Re: Possible thermostat going bad?
Post by: ducman77 on November 09, 2016, 03:10:04 pm
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??
Title: Re: Possible thermostat going bad?
Post by: Gwill21 on November 09, 2016, 05:14:44 pm
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!
Title: Re: Possible thermostat going bad?
Post by: pudding on November 10, 2016, 02:08:00 pm
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!
Title: Re: Possible thermostat going bad?
Post by: GTIEagles on November 10, 2016, 02:41:08 pm
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!

Hi Pudding.

I don't believe a manual Edition 30 has any inline thermostats, only a DSG would have one.
Title: Re: Possible thermostat going bad?
Post by: pudding on November 10, 2016, 04:47:31 pm
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!

Hi Pudding.

I don't believe a manual Edition 30 has any inline thermostats, only a DSG would have one.

Ah OK, I ordered one from the stealer earlier  :grin:  I've read manual cars have 1 main and 1 inline, and DSG has 1 main and 2 inlines.  Does that not apply to the ED30 then?
Title: Re: Possible thermostat going bad?
Post by: ducman77 on November 10, 2016, 07:35:49 pm
I thought a manual ed30 had one inline thermostat alright?
Title: Re: Possible thermostat going bad?
Post by: GTIEagles on November 11, 2016, 09:46:50 am
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!

Hi Pudding.

I don't believe a manual Edition 30 has any inline thermostats, only a DSG would have one.

Ah OK, I ordered one from the stealer earlier  :grin:  I've read manual cars have 1 main and 1 inline, and DSG has 1 main and 2 inlines.  Does that not apply to the ED30 then?

It's the earlier manual GTIs that had 1 inline <2006 but after they stopped using them.

To further complicate things DSGs had 2 inline <2006 but after just had 1!
Title: Re: Possible thermostat going bad?
Post by: pudding on November 11, 2016, 11:04:45 am
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!

Hi Pudding.

I don't believe a manual Edition 30 has any inline thermostats, only a DSG would have one.

Ah OK, I ordered one from the stealer earlier  :grin:  I've read manual cars have 1 main and 1 inline, and DSG has 1 main and 2 inlines.  Does that not apply to the ED30 then?

It's the earlier manual GTIs that had 1 inline <2006 but after they stopped using them.

To further complicate things DSGs had 2 inline <2006 but after just had 1!

Weird!  My dealer took my reg and said it showed up as having one.  Mine's a 2007.  Oh well, I'll see if I can find this extra thermostat over the weekend and if it is indeed missing one, never mind.  I'll have one available if somebody needs one  :grin:
Title: Re: Possible thermostat going bad?
Post by: lukemk5gti on January 04, 2017, 11:22:41 am
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??

Hey @ducman77 (http://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=7463)

How much work was involved in changing the inline? My main one is changed and I never had an issue with the warm up time but now it's taking a 25min drive before I get to 90 deg.

I'm manual so I just have the one.

Title: Re: Possible thermostat going bad?
Post by: v4rley on January 04, 2017, 12:12:59 pm
@lukemk5gti (http://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=10176)

I changed all my thermostat main and inline 2 years ago, now according to polar fis it's not reaching temperature  :scared:

With regard to the inline they are fairly straight forward, you will have one down the front, between your radiator and inlet manifold. I drained the coolant and undid the most reachable pipe clips at the top and bottom and pulled it out with the inline stat in the middle.
Title: Re: Possible thermostat going bad?
Post by: lukemk5gti on January 04, 2017, 12:36:53 pm
@lukemk5gti (http://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=10176)

I changed all my thermostat main and inline 2 years ago, now according to polar fis it's not reaching temperature  :scared:

With regard to the inline they are fairly straight forward, you will have one down the front, between your radiator and inlet manifold. I drained the coolant and undid the most reachable pipe clips at the top and bottom and pulled it out with the inline stat in the middle.

Thanks @v4rley (http://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=6697)

I was really hoping it was a screw on so I could rip it out handy enough without draining the coolant.

Can you do the work from the bonnet without removing any gear.... From memory there is enough space there between the engine and battery no?
Title: Re: Possible thermostat going bad?
Post by: v4rley on January 04, 2017, 12:50:29 pm
I thought the battery inline one is only for the early dsg?
Ok, if it is near the battery I managed to change with coolant still in think I bunged the pipes.

If it's down the front:

If you look at the photos in this thread:

http://www.mk5golfgti.co.uk/forum/index.php/topic,78341.msg963886.html#msg963886

The 3rd photo by dazza has removed the clamp from the bottom hose, then if you trace it back to the top of the engine bay you should be able to pull it up rather than trying to remove the thermostat between the block and the radiator
Title: Re: Possible thermostat going bad?
Post by: r5gtt on January 04, 2017, 01:13:54 pm
Weirdly enough I have a 55reg late November model and it only has two stats. One near the alternator and one on the dsg box. Some have another inline as mention but I've checked and I've not got one.
Title: Re: Possible thermostat going bad?
Post by: lukemk5gti on January 04, 2017, 02:04:33 pm
I thought the battery inline one is only for the early dsg?
Ok, if it is near the battery I managed to change with coolant still in think I bunged the pipes.

If it's down the front:

If you look at the photos in this thread:

http://www.mk5golfgti.co.uk/forum/index.php/topic,78341.msg963886.html#msg963886

The 3rd photo by dazza has removed the clamp from the bottom hose, then if you trace it back to the top of the engine bay you should be able to pull it up rather than trying to remove the thermostat between the block and the radiator

You're right!

So I just bought a hose clip pliers and now I'll get my hands on an inline stat - 4E0 121 113

I'll probably tackle this job next month when everything arrives since I cheaped out and bought the pliers for €10 from China.

Ideally I'll bung the pipes so as not to drain the coolant considering it's fairly fresh. Anything that I do lose I'll just top up with my premixed G13+
Title: Re: Possible thermostat going bad?
Post by: Pesky jones on January 04, 2017, 04:16:51 pm
To further complicate things DSGs had 2 inline <2006 but after just had 1!

Are you confident on this?
Title: Re: Possible thermostat going bad?
Post by: Pesky jones on January 04, 2017, 04:25:22 pm
Weirdly enough Rightly so I have a 55reg late November model and it only has two stats. One near the alternator and one on the dsg box. Some have another inline as mention but I've checked and I've not got one.

according to


It's the earlier manual GTIs that had 1 inline <2006 but after they stopped using them.

To further complicate things DSGs had 2 inline <2006 but after just had 1!



Title: Re: Possible thermostat going bad?
Post by: mrw on January 04, 2017, 08:37:42 pm
I believe it's only DSG's that have them over the gearbox / by the battery (Mine's a 08 DSG with one inline in that location).
Title: Re: Possible thermostat going bad?
Post by: Saintsteve on January 04, 2017, 08:58:12 pm
I've been told that the 2.0 TFsi engines may also suffer with a just a faulty temperature sensor and not the thermostat giving the faulty temp readings. This is a very cheap fix and worth checking before assuming it's the main engine thermostat.

A point worth remembering , if you have a remapped engine, that's also been tuned, your engine will not be producing full power if the engine temps are too low.
I know that R Tech maps have 5 different power settings depending on engine and intake temps readings, that if your running around at 75 degrees, you remap will not be selecting Map 5 or most powerful output one ) .Also as has been mentioned your MPG will suffer if the engine isn't at optimal Readings. :happy2: