[sunsetorange]

I have a Polo GT TSi, bought in 2016. It has run around 70,000 kilometers and had undergone mechatronics change under add on warranty.

Over a period of 2 weeks, I have been noticing a steady rise in engine temperature even during short runs. It usually remains at 90 degrees C no matter how long or how hard it had been driven. These days, it has started rising to 100 and 105 degrees and the AC cooling was failing. On seeing the rise in temperature, I used to switch off the AC compressor and slow down a bit, upon which the temperature returned to 90 degrees.
I even took to running the car with the windows down and AC off, but to my chagrin, I found the temperature rising even if I do 2-3 kilometers at about 60 -80 kmph.

Throughout all this I was checking for any telltale signs of coolant leak - decreased levels in the reservoir/ splashes of coolant in the engine bay, but found nothing!

I called up to Ramani VW ( dealer here in trichy) and explained about my problem and asked for the car to be picked up on the 10th of june. They checked the car and repeated what I told them- " No decrease in coolant levels or any noticeable leaks". I told them to take a thorough look and get back to me. They called me up the next day and said they have checked the cooling system under pressure and found a tiny leak in the O-ring of the coolant pump. They placed an order for the same and it was replaced on arrival. They checked the car and said the issue has been resolved, raised the bill and sent the car to me. Fortunately, I reached home when the car was being delivered and took it out for a test drive. I had hardly driven 500 metres when the temperature started rising again!. I called up the service assistant and told him nothing has changed after the replacement of o- ring. I sent the car back with the driver.

The service assistant called me back in the evening and said they have thoroughly checked everything and could find no leaks. He had a hypothesis that there would have been an air pocket lodged in the coolant pump or water pump and so they dismantled everything in the cooling system and reassembled them. This took 2 more days. Finally he called me up today and says the issue persists and they have raised a query with VW about the complaint and are awaiting further instructions.

My wife uses the car and has been managing by hitching rides from her family over the last week.

One week has passed and I am nowhere near getting my car back.

What could be the problem? Any ideas?

[Rshrey22]

It could be a bad thermostat valve. That should be the first thing which needs to be checked.

Followed by Radiator Fan, sometimes people forget to check whether radiator fan is turning on or not since nowadays it is hidden by the shroud covering the radiator from the back. Car has covered 70k kms, so it is possible that the radiator fan motor has failed.

It could also be a clogged radiator, which can be easily cleaned at your local FNG for Rs. 500-700/- . It is taken out and the channels are cleaned with wire.

Also, get your ac condenser and radiator pressure washed by an AC service guy. Maybe you haven't gotten these cleaned in a long time. Dust accumulation does increase the burden on cooling system

Worst case scenario, the water pump has failed.

[govigov]

The cooling system should be able to hold pressure, that is how they keep the temperature in check by refusing the water to boil. Usually, in older cars, it is the radiator cap not able to hold the pressure. But not sure in your case what would be the reason.

[dhanushs]

Originally Posted by sunsetorange

...

One week has passed and I am nowhere near getting my car back.

What could be the problem? Any ideas?

The initial problem could've been the O-ring of the water pump or water pump itself, but, since they've changed it and checked pretty much everything, I think the initial heat-up has caused a head gasket failure. Do check it out.

[R2D2]

Please have your service centre check correct operation of the following:

a) Thermostat valve
b) Radiator fan operation
c) Clogged radiator (leaves and other debris)
d) Coolant pump

I assume you have been using OEM coolant and not topped off coolant with tap or bore-well water.

[sunsetorange]

Originally Posted by Rshrey22

It could be a bad thermostat valve. That should be the first thing which needs to be checked.


Followed by Radiator Fan, sometimes people forget to check whether radiator fan is turning on or not since nowadays it is hidden by the shroud covering the radiator from the back. Car has covered 70k kms, so it is possible that the radiator fan motor has failed.

The fan is a bit noisy, but works ( don't know if it is effective). I will ask them to check the thermostat valve out.

Originally Posted by dhanushs

I think the initial heat-up has caused a head gasket failure. Do check it out.

I will ask them to check it out.

Originally Posted by R2D2

Please have your service centre check correct operation of the following:

a) Thermostat valve
b) Radiator fan operation
c) Clogged radiator (leaves and other debris)
d) Coolant pump

I assume you have been using OEM coolant and not topped off coolant with tap or bore-well water.

It has been topped up only using the OE coolant premix. Will update when I have feedback.

[R2D2]

Originally Posted by sunsetorange

The fan is a bit noisy, but works ( don't know if it is effective). I will ask them to check the thermostat valve out.

It has been topped up only using the OE coolant premix. Will update when I have feedback.

Thermostat operation is relatively easy to check yourself if done 1st thing in the morning with a cold engine only, never with a hot engine. Take off the radiator cap, start the engine. Look into the neck of the radiator and you will find coolant more or less stagnant and not flowing that's because of the valve being closed. Wait till the engine heats up (check temp gauge on the dash) and then watch the coolant in the radiator neck. This way you also release any airlocks or air pockets in the system. Also the radiator fan should come on when the engine is hot and car is stationary.

If it is still appears stagnant, i.e. not flowing at all or smoothly it can be one of 2 things either your water pump is not operating properly OR the valve is suspect. If your pump is belt driven please ensure proper belt tension as per specs. Also, pulleys and belts should not be damaged or coated with engine oil or other substance.

[shifu]

Just a pointer - I had the exact same issue in my 2016 Vento TSI. And I have helped another friend diagnose it for his 2018 Polo TSI.

There is a solenoid that instructs the radiator fan to start when the coolant temperature reaches a particular temperature. That solenoid intermittently stops working. There is a way to bypass that solenoid, so the fan will always run. At the Service center, the technician bypassed the solenoid and asked me to run for couple of days. If the temperature is not crossing 90 C, then we know for sure that the issue is with that.

The solenoid is covered under warranty, if you still have it. It costs around 8K, and including labor the total bill came around 10K.

[sunsetorange]

Originally Posted by R2D2

Thermostat operation is relatively easy to check yourself if done 1st thing in the morning with a cold engine only, never with a hot engine.

Will try this if yet unresolved.

Originally Posted by shifu

Just a pointer - I had the exact same issue in my 2016 Vento TSI.

The solenoid is covered under warranty, if you still have it. It costs around 8K, and including labor the total bill came around 10K.

Will keep in mind.
The service assistant called me yesterday that they have got instructions to change the waterpump and has placed orders for the same. It would be arriving today ( 18/06/22) and would be replaced, followed by a long testdrive before being returned to me.
The water pump was replaced about 10 months ago and would hence be replaced under warranty. Let's see how this pans out.

[sunsetorange]

The water pump was replaced and the car was tested again which showed no increase in temperature. It has been delivered and I did a drive of about 15 km with the delivery driver. There was no further increase in temperature of decreased in AC effectiveness. It was indeed the water pump.
I guess that has resolved the issue. Thanks for the guidance folks. Moderators may please close this thread .

[asit.kulkarni93]

Originally Posted by sunsetorange

The water pump was replaced and the car was tested again which showed no increase in temperature. It has been delivered and I did a drive of about 15 km with the delivery driver. There was no further increase in temperature of decreased in AC effectiveness. It was indeed the water pump.
I guess that has resolved the issue. Thanks for the guidance folks. Moderators may please close this thread .

Good to know that the issue has been resolved but did you check with them about the reason for the the water pump failure again?

[sunsetorange]

Originally Posted by asit.kulkarni93

Good to know that the issue has been resolved but did you check with them about the reason for the the water pump failure again?

They didn't give a reason. Just that it wasn't functioning optimally. I will ask them later and find out.

[Crhysis]

I also have a 2016 Polo GT TSI (46,000 kms) that my wife is dependant on. Have had the exact same issue and have followed a similar series of events - Coolant temperature light warning, engine temperature rising, no decrease in coolant level, went to service center, after 2 days they informed me of the leak from the pump, got it replaced, flushed the coolant, tested and the car was sent home. The next day the issue cropped up again and now my car is back at the service center for round 2. Hopefully it gets fixed this time. Will ask them to check the points mentioned in the thread.

[pgoyal1996]

I had the same issue a month back in my vento. The temperature skyrocketed with a flashing over heat symbol. The coolant was splashing like anything and when I checked the fan wasn't running.

Since, I for a fact knew that if the temps are high, the radiator fan continues to run for some time even after the car is locked. So, that was the conclusing point.

I checked for the radiator fan fuse (30 A fuse at the battery terminal) and it was surely blown. I had a spare 40A fuse and fitted the same. The car has been running great since, there has been no major, follow up defect or breakdown(touchwood).

My, recommendation would be check the basics first.
I understand that you might have gone through the same but, no harm in making a second/follow up check.

Hope this is of any help.

[Jeroen]

Glad to see this issue was resolved. Just a comments about a small leak as a possible cause for a high temperature in a cooling system. It is physically impossible.

A small leak will and can not affect the temperature of the coolant. Modern cooling systems are closed, which means that as the coolant warms up, the pressure inside the system rises. The higher pressure means the boiling point of the coolant is raised to. So instead of 100oC it now becomes 110oC.

Always check the four points as suggested by R2D2. Those are the most likely causes. If found in order the last suspect tends to be the pump. Over time the impeller might wear down and this decreases the capacity of the pump. Less coolant is going around and temperature can rise.

If you have a temperature gauge on your display you might be able to observe the opening of your thermostat. Try this a few times, when the engine is still running fine, so you have a reference for when things go wrong.

Check out the last bit of this post and the little video

https://www.team-bhp.com/forum/diy-d...ml#post5327034

Jeroen