Guide to changing Engine temperature sensor on Polo MKV 6n2

Post Instructions on DIY modifications here - use all information with caution!
NickP
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Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by NickP »

Needed to change mine recently cos the car wasn't starting properly when cold. It turns out the sensor had gone so the auto-choke wasn't kicking in.

Required:
-Temperature sensor
-Antifreeze
-Rubber washer (optional)
-Horseshoe clip (optional)

Image

You only actually need a new temperature sensor but I decided to get the washer and horseshoe clip incase I broke anything. Came to £20 in total including the antifreeze from Eurocar parts

Partially drain radiator
WARNING MAKE SURE RADIATOR IS COOL, DO WHILST ENGINE HAS BEEN OFF FOR AT LEAST AN HOUR
First things first you need to drain off the radiator. No need to do the whole thing, just enough so there's not much left near the sensor when you pull it out.

The sensor can be found just to the right of the engine cover. It's the green socket with the black casing round it
Image


The easiest thing I found to do was first remove the lid fromt the radiator refill, do this very slowly in case their is any built up pressure. Then rather than removing all the coolant I just undid the overflow pipe connected to the reservoir, see below. To undo the pipe you need to firmly squeese the blue clip then slide it down the pipe. Twist the pipe side to side until it comes off.

Image

Dangle this down as low as it will go i.e. quite a bit below the level of the sensor, then drain as much coolant as possible off into a container. You'll need to encourage it, I did this by both squeesing some of the bigger radiator pipes to the right of the sensor and by also get an innocent bystander to put the lid back on the reservoir then blow through the plastic tube from where the pipe has been removed. Make sure you put something round this like kitchen towel because anti freeze is poisonous)

When you've drained off as much as you can, for me I filled about 1 and a half wine bottles, then lodge another container underneath the sensor to catch any excess, I used a pirex jug, see below
Image

Now you need to remove the horsehoe clip holding it on with a pair of plyers
Image

Pull the sensor out slowly catching any excess fluid in the container. Make sure you get the rubber washer, I replaced mine but the original still looked perfectly fine. You now need to remove the sensor from the black housing. There's probalby a better way to do this but if you look at your new sensor you can see a raised edge, this needs to be unclipped from housing, I did this with a small flat screwdriver.

Replace the sensor then push back in. Put the horseshoe clip back on

JOB DONE!

Now all you need to do is replace the coolant that has been removed. I actually re-used the stuff I'd taken out and topped it up with a bit of anti-freeze. My new anti-freeze is blue and my old red, I don't think it matters if you mix them but I read that you can test this by mixing some and if the new solution goes brown then they're not compatible but this sounds like a load of coblers. I did it anyway and it looked ok.

Now run your engine for about 5 mins with the reservoir cap off, this allows any bubbles in the system to be removed, also make sure there are no leaks coming from the sensor.

This is really easy to do, I'm a novice and it only took me about half an hour. If anyone has any trouble drop me a PM. Hope this helps out.
specializedgreg
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Post by specializedgreg »

Just like to add that the GTI is slightly different to the one shown here. The actual sender is on the left hand side, with one of the rad pipes right next to it. No need to drain any of the system, just pull the horseshoe clip up, wrench it out and throw the new one in quick you'll probably lose about half a litre if you're quick about it.
BlooPolo
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by BlooPolo »

Thanks for the guide and pics. Came across this whilst looking for details on replacing a (possibly) stuck thermostat resulting in cold readign when moving and normal reading when idle/standstill. Are the 'thermostat' and this coolant sensor the same thing or sensors from different parts of the engine?
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Tim_GTi
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by Tim_GTi »

No this is the temp sensor, Thermostat is a different thing. It's located in the plastic casing which this sensor plugs into (I would heavily assume so anyway).
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alexperkins
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by alexperkins »

You should never mix blue and red coolant - thats a big big no no. Its like mixing green and red coolant. You should never add green to red, same as blue to red. Blue coolant doesnt have corrosion inhibitants, and isnt compatible with G12 coolant - if you are running G12, you should top up with G12 to ensure maximum efficiency and avoid damage.

And yes tim you are right - its located in the thermostat housing which is where the sensors plug into.

Also, to change the green sensor, you dont need to remove the cap or drain any coolant out of the system. Its a vacuum based system - leaving the lid on makes much less mess and prevents an airlock more so. When you have refitted the new sensor, start the engine with the cap off, and squeeze the big radiator hoses a few times which should remove any bubbles.
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Tim_GTi
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by Tim_GTi »

Ah i wasn't aware you couldn't mix coolnats, tha saves future embarassment! Some coolant does come out of the plug once the sensor is out though, so be quick!
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by stevan »

this is a great forum ! have this fault know no how to sort it great stuff! :D
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by oliver12 »

what engine is that on ? has i have a 1.4 8v p reg and my sensor is on the left side ?

my temp goes to normal when stationary but when driving its zero does this mean my temp sensor needs changin?

thanks
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alexperkins
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by alexperkins »

Sounds like the sensor is fubarred mate. That engine is a 6n2 - thermostat housing position changes between models.
LynoMaho
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by LynoMaho »

Nickp and the rest of you,

I had the same problem initially spent €270.00 on a new starter, problem persisted and I brought the car back. I was then told it was the bushing in the gear box and maybe the clutch, I thought the guy was takin the micky. He sait it could be an extra €450.00 to fix them both. :evil:

I then logged in and started wandering the net and found this forum. I ordered the part for €30.00 and change it myself the next day. :D

Obviously I told the garage where to go and saved myself getting screwed. :D :D :D

Thanks lads.

Jimmy
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by Prabz »

Hi guys i think i have similar problem... What it is when started the car and driving the temperature will start to go up... but when driving for a little while it sits just under the half way line... then when driving for like 20 mins or so it drops right down to the bottom... Another thing is the needle doesn't go to the middle it sits just under it... Wondering if anyone could help me ?
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Tim_GTi
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by Tim_GTi »

same issues i had, my temp gauge was acting funny, i changed the temp sensor and it was all sorted!
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Re: Draining off

Post by pberry »

specializedgreg wrote:Just like to add that the GTI is slightly different to the one shown here. The actual sender is on the left hand side, with one of the rad pipes right next to it. No need to drain any of the system, just pull the horseshoe clip up, wrench it out and throw the new one in quick you'll probably lose about half a litre if you're quick about it.
Do drain first: it's annoying but necessary. I didn't and had to catch most of it issuing from the sensor socket when I pulled the plug. Whatever you lose on the ground you have to top up so best to do it properly!
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by JTLondon »

is this guide applicable for a 98 R reg 6N?
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alexperkins
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Re: Guide to changing Engine temperature sensor on Polo MKV 6n2

Post by alexperkins »

Its similar, but take the instructions with a pinch of salt as the engines have a different layout mate.
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