2008 1.4i polo 9n heavy on petrol

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

Thats the part :thumbup:

DM me you cell number, I'm chatting to a mate in DBN who might be able to help you have a proper look at this issue.
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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

IS the car behaving since the coolant sensor was changed?
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1980 - VW MK1 GT - 1.8 Carb - https://www.vwclub.co.za/forum/viewtopi ... 1&t=153861
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Re: 2008 1.4i polo 9n heavy on petrol

Post by VAG Fan »

EX-DOHCTOR wrote: Sat Sep 11, 2021 1:32 pmTemperature gauge measures the water and coolant temperature in circulation in the water cooling system. Like the water pump... nothing to do with fuel consumption at all.
I beg to differ with the "nothing to do" part. The temperature gauge shows the input from the temperature sensor, and the ECU uses the same signal (or a second signal from the same sensor) to calculate how much fuel to inject. If the sensor gives a wrong "cool" or "cold" reading the whole time, then the ECU enriches the air-fuel mixture.

However, in my experience, a defective temperature sensor normally doesn't cause the gauge to hover at the quarter mark. Normally it has the gauge falling completely to zero. The fact that the OP's gauge is showing quarter, could in fact point to a defective thermostat that is essentially stuck open. The engine will only warm up properly when stuck in slow traffic. As soon as there is air flow through the radiator, the engine cools down most of the way. The ECU would then add extra fuel to the mixture.

@ OP - TL;DR :
If the new sensor behaves in the same way as the old one, then very likely the problem is with the thermostat.
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

EX-DOHCTOR wrote:IS the car behaving since the coolant sensor was changed?
I've managed to change the sensor last night. So today whilst coming to work I've noticed that once the guage reaches 90°c,it stays constant and not swing up and down as it used to. On my way home today I will double check and I will update you just to make sure it stays constant as I won't be in slow moving traffic and it'll better to see if it's sorted for good

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

OK great. Lets see how it behaves the rest of the week.

I was worried that we would need to look at the Thermostat next and that is not something I would attempt a DIY on.
I let the dealers sort mine out, also required and flush and coolant refresh.

As I recall they changed the entire thermostat housing with the thermostat. I cannot for the life of me remember why we did that though.
It was well over 10 years ago.
2014 - VW Jetta 6 - 1.6 TDi DSG
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

Yes, I will take it for a long drive this evening to make sure it's working as it was supposed to.

Fingers crossed its sorted and I wouldn't need to go as far as changing the thermomstatbut we will know by this evening

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

Maybe lets watch it over the next few days, just to be sure.
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Re: 2008 1.4i polo 9n heavy on petrol

Post by n.gov3 »

EX-DOHCTOR wrote: Tue Sep 14, 2021 11:25 am OK great. Lets see how it behaves the rest of the week.

I was worried that we would need to look at the Thermostat next and that is not something I would attempt a DIY on.
I let the dealers sort mine out, also required and flush and coolant refresh.

As I recall they changed the entire thermostat housing with the thermostat. I cannot for the life of me remember why we did that though.
It was well over 10 years ago.
A friends polo, 2007 model 1.4, displayed similar symptoms to this one. Ended up being the thermostat which I replaced. Wasn't too bad doing so..... Ended up getting the replacement from vw for 1.2k ( pricing from around 2015)
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

n.gov3 wrote:
EX-DOHCTOR wrote: Tue Sep 14, 2021 11:25 am OK great. Lets see how it behaves the rest of the week.

I was worried that we would need to look at the Thermostat next and that is not something I would attempt a DIY on.
I let the dealers sort mine out, also required and flush and coolant refresh.

As I recall they changed the entire thermostat housing with the thermostat. I cannot for the life of me remember why we did that though.
It was well over 10 years ago.
A friends polo, 2007 model 1.4, displayed similar symptoms to this one. Ended up being the thermostat which I replaced. Wasn't too bad doing so..... Ended up getting the replacement from vw for 1.2k ( pricing from around 2015)
By any chance did replacing the thermostat improve the fuel efficiency on your friends car aswell?




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Re: 2008 1.4i polo 9n heavy on petrol

Post by n.gov3 »

Neeven wrote: Tue Sep 14, 2021 4:24 pm
n.gov3 wrote:
EX-DOHCTOR wrote: Tue Sep 14, 2021 11:25 am OK great. Lets see how it behaves the rest of the week.

I was worried that we would need to look at the Thermostat next and that is not something I would attempt a DIY on.
I let the dealers sort mine out, also required and flush and coolant refresh.

As I recall they changed the entire thermostat housing with the thermostat. I cannot for the life of me remember why we did that though.
It was well over 10 years ago.
A friends polo, 2007 model 1.4, displayed similar symptoms to this one. Ended up being the thermostat which I replaced. Wasn't too bad doing so..... Ended up getting the replacement from vw for 1.2k ( pricing from around 2015)
By any chance did replacing the thermostat improve the fuel efficiency on your friends car aswell?


Definitely would have as the engine would have then being maintaining optimum operating temp

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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

n.gov3 wrote:
Neeven wrote: Tue Sep 14, 2021 4:24 pm
n.gov3 wrote:
EX-DOHCTOR wrote: Tue Sep 14, 2021 11:25 am OK great. Lets see how it behaves the rest of the week.

I was worried that we would need to look at the Thermostat next and that is not something I would attempt a DIY on.
I let the dealers sort mine out, also required and flush and coolant refresh.

As I recall they changed the entire thermostat housing with the thermostat. I cannot for the life of me remember why we did that though.
It was well over 10 years ago.
A friends polo, 2007 model 1.4, displayed similar symptoms to this one. Ended up being the thermostat which I replaced. Wasn't too bad doing so..... Ended up getting the replacement from vw for 1.2k ( pricing from around 2015)
By any chance did replacing the thermostat improve the fuel efficiency on your friends car aswell?


Definitely would have as the engine would have then being maintaining optimum operating temp

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Okay cool thanks.

Do you remember what symptoms he was having for him to change the thermostat?

I want to make sure that it's that so that I know it's worthwhile as the part itself is abit costly



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Re: 2008 1.4i polo 9n heavy on petrol

Post by n.gov3 »

Used to hover well below 90 deg on the highway and just about get to 90 deg in slow moving traffic. Once the thermostat was replaced, it was back to normal
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

Okay thanks, I may have to look at getting a new one, but after changing the sensor and the engine getting warm, the guage stayed in the Centre the whole trip so it could have been that but I will monitor it.


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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

I was also told that there's 2 pipes and 1 needs to be hotter than the other, however when I checked mine, both were the same temperature

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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

EX-DOHCTOR wrote:Maybe lets watch it over the next few days, just to be sure.
Okay update on the situation.

I've noticed that the guage is staying on the half way mark when I'm driving short distances(robot to robot), however when I'm on the highway and driving about 120 km or less, I can see the guage slowly going down to the quarter mark.

The route I use to work isn't long enough on the Pic below it just started decreasing as I was on the highway, but this weekend when I drove to Chatsworth I noticed it was on the quarter mark majority of the way

Image

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

When you get off the highway and stop at a robot or idle the motor, does the needle move back up to 90’c?
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

EX-DOHCTOR wrote:When you get off the highway and stop at a robot or idle the motor, does the needle move back up to 90’c?
Yes, when I either stop or wait at the robot then I see the needle will slowly go back to the 90°C mark

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

OK, So think that is normal functioning.

You sit in traffic, engine warms up, then hit the highway and the thermostat opens and the engine cools down, stop again and the engine warms back up.
Lets monitor for a few more days and see, but I think we might've solved that issue for now.

Your car is a Trendline correct?
Meaning there is no MFA on the car?

I'm just wondering how you got the fuel consumption readings?
2014 - VW Jetta 6 - 1.6 TDi DSG
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1980 - VW MK1 GT - 1.8 Carb - https://www.vwclub.co.za/forum/viewtopi ... 1&t=153861
1971 - Mitsubishi Colt 1100F - https://www.vwclub.co.za/forum/viewtopi ... 1&t=220503
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

Okay is it normal for the guage to stay at the quarter mark when on the highway though? Or must it always stay on the halfway mark

Yes the car is a trendline, I don't know what's a MAF though

Okay so regarding how I calculated the fuel consumption, at first I used to top up the tank and used to drive till the tank is almost empty and it would only give me about 540kms out of 49 litres of petrol.

Then I used to fill it up halfway and run it till its almost empty and still average around the same km per liter

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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

OK so the MFA for the onboard computer to display various information on the window where your digital odometer readings are.

Some of the screens will show current fuel consumption, average fuel consumption and range on current fuel tank, which will be influenced by the readings displayed on the current and average fuel consumption.

I used to get around 600km's on a tank on my 1.4i 9N fairly regularly, mostly open road driving. So what you're getting with a mix of highway and in town driving sounds fairly normal.

Depending on the calculations you're using and the sample size of the data, I suspect the mileage you're getting is correct for the driving you're doing.

Now for the current behavior of the temp gauge needle, Its been a long time since I've driven a 9N/9N3 but I think its behaving correctly now. As long as it isn't swinging all the way to 0'C and then back again I think you should be ok there.

I'd hate for you to go and replace the thermostat only to end up in the same place again for example.
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1980 - VW MK1 GT - 1.8 Carb - https://www.vwclub.co.za/forum/viewtopi ... 1&t=153861
1971 - Mitsubishi Colt 1100F - https://www.vwclub.co.za/forum/viewtopi ... 1&t=220503
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Re: 2008 1.4i polo 9n heavy on petrol

Post by EX-DOHCTOR »

Forgot to mention, if you have the MFA option on the car, one of your stalks will have a button on the end that allows you to swap between the screens. I think its on the right stalk.
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

Okay then yes you are correct, my car doesn't have a MFA, I went to have a look now but it has no other options there.

With regards to the fuel consumption it could be you're correct about the fuel consumption then as I didn't take into consideration how much time I spend in traffic and the vehicle idling aswelll.

I was under the impression that the needle needs to stay on 90°C once it's warmed but if it's supposed to drop abit whilst on the highway then it could be that it's reading correctly as you pointed out because it never dropped to 0°C before.

It's a good thing you had explained this before I got another thermostat when there's no need replacing it

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Re: 2008 1.4i polo 9n heavy on petrol

Post by n.gov3 »

Neeven wrote: Wed Sep 15, 2021 11:02 am Okay then yes you are correct, my car doesn't have a MFA, I went to have a look now but it has no other options there.

With regards to the fuel consumption it could be you're correct about the fuel consumption then as I didn't take into consideration how much time I spend in traffic and the vehicle idling aswelll.

I was under the impression that the needle needs to stay on 90°C once it's warmed but if it's supposed to drop abit whilst on the highway then it could be that it's reading correctly as you pointed out because it never dropped to 0°C before.

It's a good thing you had explained this before I got another thermostat when there's no need replacing it

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I suspect that you have a dodgy thermostat..... Gauge should stay at 90 deg on the cluster even if there's small deviations in actual water temp. Vw designed it that way.

On fuel consumption, I normally fill up to the auto stop and then check how many km I would get when I then fill to the auto stop, again. Most accurate that way
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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

n.gov3 wrote:
Neeven wrote: Wed Sep 15, 2021 11:02 am Okay then yes you are correct, my car doesn't have a MFA, I went to have a look now but it has no other options there.

With regards to the fuel consumption it could be you're correct about the fuel consumption then as I didn't take into consideration how much time I spend in traffic and the vehicle idling aswelll.

I was under the impression that the needle needs to stay on 90°C once it's warmed but if it's supposed to drop abit whilst on the highway then it could be that it's reading correctly as you pointed out because it never dropped to 0°C before.

It's a good thing you had explained this before I got another thermostat when there's no need replacing it

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I suspect that you have a dodgy thermostat..... Gauge should stay at 90 deg on the cluster even if there's small deviations in actual water temp. Vw designed it that way.

On fuel consumption, I normally fill up to the auto stop and then check how many km I would get when I then fill to the auto stop, again. Most accurate that way
Meaning once it's warmed, it should stay on the 90°C mark even when driving on the highway?

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Re: 2008 1.4i polo 9n heavy on petrol

Post by Neeven »

This weekend I took a 45km trip, whilst on the way the needle would go to 90° and then to the quarter mark and back. Is that normal or was it supposed to stay in the middle the whole trip?

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