2007 Polo Coolant temperature sensor warning

[VWScully]

Hiya everyone;
This is my first Post here . I have a 2007 Polo and I am wondering if the Temperature sensor is going wonky.
I was driving a few months ago back to Reading from Wales, and suddenly it got really cold in the car despite the heating being on full. It was like that for a few minutes and then went back to being warm. It did that a few times since then and I was wondering if it was the thermostat.

However, today I was driving from Wales to Manchester and was stuck in a traffic queue when suddenly the coolant alarm came on and the temperature gauge was reading into the red zone.
I was about to pull into the nearest layby when suddenly it returned to normal

I stopped at the next fuel station, checked the coolant level and it looked fine. Engine didn't seem to be overheated either.
WTF? Could it be temperature sensor??
I need to drive to Snowdonia next week so need it sorted asap .
Cheers for any advice!

[CarbonChaos]

Hi and welcome to the forum,
You say you have a 2007 polo but didn’t state what engine it has ? So this can only be a best guess.
First point if the interior heater is blowing hot then cold it could be blocking ? Did you notice the gauge at this point ?
Second point this could be a stuck thermostat ?

My advise would be to replace the thermostat and coolant and see how that goes,a good coolant flush at the same time would not hurt also.

You also need to check the operation of the radiator fan they are known fail with broken wiring

[VWScully]

Oh cheers thanks .
It's a 1.2l Petrol engine.

[RUM4MO]

Just to add in my thoughts, if everything wrt the engine cooling system is okay, wrt only the heater blowing hot and then cold etc, it might be due to a faulty temperature flap motor, I've never had a VW Group car that just had manual cabin air system, though I'd think they will use a temperature flap to regulate cabin temperature.

Make sure that you only ever use compatible coolant as using the wrong type can end up with jellyish stuff forming, aim to buy only G12, G12+, G12++ or G12evo - and not G13 as it has been discontinued by VW Group and seems to be a bit troublesome over a long period in use.

[VWScully]

Thanks.

Do you reckon the two things are related though? I have had the warm/cold/warm thing happen a couple of times in the past few months, but hadn't ever had the temperature guage go up or the alarm sound until this recent incident.
I can't get to a Garage this week and have to get back to Reading after Snowdonia so am going to risk it (I hope that isn't famous last words ). However, I am meeting a friend and have my RAC memerbship fully paid up :p.

Is there an easy way to check the Thermostat? I had replaced it on my Mk2 Golf once and it was quite an easy job! That was a 1.8l motor and the symptoms were similar; very cold in the cabin sometimes despite the heating being on, but I never had a temperature alarm or elevated reading on the gauge. (To be fair, I was never in a long traffic queue with that car either! )

Thanks for the help .

[Johntheo1]

The VW temperature gauge doesn't give a lot of useful information. It will read the correct temperature up to 75C, once it reaches this temperature it will rapidly rise to exactly 90C and remain there until either the actual temperature exceeds 107C or falls back again to < 75C, you may have two unrelated problems, if the cooling fan isn't operating for whatever reason then the temperature will apparently shoot up from 90C to > 107C (while idling) so suggest after a fairly long run to just leave the car idling in your driveway or where ever, lift the bonnet and wait for the cooling fan to cut in.
The other potential problem may be the thermostat but if so and assuming the temperature sensor OK then you should see the temperature gauge falling to 75C or lower as IMO you should still have reasonable cabin heating down to 75C, certainly not cold.