Temperature gauge fluctuates from 70-90, thermostat?

[its_neil]

Hi guys,

My car for some reason seems unable to sit at 12 o'clock on the temperature gauge, it never goes above 12 o'clock (90 degrees) but just slowly fluctuates between about 70 and 90. I know that although the car isn't overheating that this behaviour isn't right but what could be causing it? Could it be the thermostat?

[Wolf Burger]

Yes, or coolant temp sensor.

I changed the coolant sensor and it is still doing exactly the same as you describe.

I am changing the thermostat next.

[Meallbhan]

For the sake of about £25, I would change the sensor first. It is way easier to do than the thermostat and only takes a minute or two. And you don't have to drain the coolant.

The main thermostat is slightly different, you need to remove the alternator for easy access and was a bit of a pain to do.

[will_15]

Mine started doing this at the weekend.

Anyone have coolant temp sensor part number?

[doylebros]

Mine started doing this at the weekend.

Anyone have coolant temp sensor part number?

Look here

http://www.partscats.info/volkswagen/en/?i=cat_vag_models&brand=vw&number=1714&set=1728&ein=2007&f=474&hauptgr=1234567890&hg=9&grf=091940249&bf=91940&hgug=919&ug=19&parent_id=2361269

06A 919 501 A - £38.62 inc vat full retail - 2 pin black 20 mm

N903 168 01 O-ring Seal - £0.54

[Human Joist]

Bet you a million pounds it's the main thermostat. Your car has 2. Or 3 if it's a dsg. The 2 small ones are inline. The main thermostat will cause the temp issues. To help diagnose it. Does the car temp get higher towards 90 when in traffic then drop when you drive.

[doylebros]

Bet you a million pounds it's the main thermostat. Your car has 2. Or 3 if it's a dsg. The 2 small ones are inline. The main thermostat will cause the temp issues. To help diagnose it. Does the car temp get higher towards 90 when in traffic then drop when you drive.

Attach a link of your thread - you'll be helping them a great deal

[Human Joist]

This is one of the links. Will try and find others. Worth a read of them all to diagnose your issue
http://www.mk5golfgti.co.uk/forum/index.php/topic,77085.0.html

Have a look through this too. There a few links to other threads. I found the more I read of others with similar problems helped my pinpoint the problem with mine. Mine turned out to be the two inline thermostats. As the car took ages to warm up. Now they are swapped its warm to 90 in 2-3 miles max. Even in this wether.

http://www.mk5golfgti.co.uk/forum/index.php/topic,76566.0.html

[its_neil]

Cheers guys,

Mine is a 2005 with DSG and yes, it goes up and drops when you start to drive a bit faster (i.e so if you've been queueing in town it'll sit about 90 but as soon as you speed up onto the motorway it drops)

Would this have any effect on the car? I.e MPG and whatnot?

[jamma]

Cheers guys,

Mine is a 2005 with DSG and yes, it goes up and drops when you start to drive a bit faster (i.e so if you've been queueing in town it'll sit about 90 but as soon as you speed up onto the motorway it drops)

Would this have any effect on the car? I.e MPG and whatnot?

mines a 2005 with DSG and I am having mine changed saturday it does exactly the same. 90 in standstill and 70 when you are driving.

[OSB]

Cheers guys,

Mine is a 2005 with DSG and yes, it goes up and drops when you start to drive a bit faster (i.e so if you've been queueing in town it'll sit about 90 but as soon as you speed up onto the motorway it drops)

Would this have any effect on the car? I.e MPG and whatnot?

I had the main stat changed a few months ago - up to temp in about 3-4 miles in this cold weather. It never really got up to 90 before, except on motorways.
MPG improved by about 2. Performance seemed better as well. My understanding is the ECU holds back power until the engine is at the right temp. Therefore if its not up to temp not all the power is available.
The job is long and a bit fiddly - VW book time is 3 hrs!

When the weather gets better I'm going to change the 2 smaller inline stats as well. This speeds warm up time as well.

What crap designs they must be! I can't remember changing a stat in the last 25 years! A few in 'the old days' though.....

[SkyJawa]

Loads of cars suffer crap stats now.  Had to have the main and egr ones done on my BM :(

Is there a how to anywhere for those 2 regulator replacement?  VW changed the main stat but refused to do the smaller 2..........

[OSB]

Loads of cars suffer crap stats now.  Had to have the main and egr ones done on my BM :(

Is there a how to anywhere for those 2 regulator replacement?  VW changed the main stat but refused to do the smaller 2..........

Yes there's loads on it here, especially recently. Have just tried to find it but the search wont work!
Have a go yourself. I'll try again in while

[Meallbhan]

There was a thread on here a month or two ago by itguy, it was a very good one. It won't sort your fluctuation problem though. The thread is for the inline regulator/s. If you have DSG you will have two inline regulators, if you have a manual, there is only the one.

These only effect the length of time the car take to warm up, if you car takes ages to warm up in cold weather, one or both of these are to blame. Your fluctuation is caused by a knackered main thermostat which is attached to the block. I have had both problem, now both are sorted  thank god!

[Human Joist]

As above. The link I posted was for the two inline stats. I know you said yours does not maintain temp but if it takes more than 3 miles to get warm it will be the inline stats as well as the main stat. If that's the case let me know and I can put a guide up for those.