[1.6 FSI] - Headgasket or simply Trigger's Broom

I did check on 7Zap, and the reservoir cap, which I assume is the fail safe pressure relief, is the same on an FSI as a 1.4 petrol, so pressures must be similar. The air in the reservior acts as a spring, allowing the coolant to expand by compressing the air in the reservior.
Mac.
@Evripidis
Although there is little chance of coolant freezing where you are located, but you still need to use G12/13/13+ at a minimum of 33% dilution, to ensure it's ability to increase the coolant's boiling point, not to mention the anti corosion property.
Mac.
 
Hi all,

I am back with some more and I am hoping that someone can shed some light:

1. My sniff tester has finally arrived. I have done the test 4 times and the magic liquid has not changed colour. I have done it when cold, when warm and after taking the car for a short drive and back. There appears to be some fluctuation caused by the air stirring when revving the car but other than that nothing.

2. If I leave the car idling for long enough the coolant will overflow the tank, cap on or off makes no difference. The radiator hoses will begin to harden but not rock hard or buldging.

3. While testing, I noticed that the fan will never kick in. I've done the output test with VCDS and the fans will turn on at all speeds.

4. I have unplugged the coolant temp sensor at the bottom radiator hose so that the fan will stay on continuously. I then left the car idling for about 30 minutes with the coolant cap on and the level remained within limits without overflowing.

5. Can anyone suggest a set of observations in VCDS to help me troubleshoot this? What are the measuring blocks for the temperature and at which point should the fan kick in and what is the telltale block?

Bonus picture:
viber_image_2023-02-17_21-13-25-927.jpg
 
The symptoms you are describing match what I have been seeing in our A7...it was gradually getting worse until pressure build up made the hoses pop out. Blown head gasket unfortunately in our case, however the fluid test you did should indicate this. Not very helpful I'm afraid, but at this point I don't have other explanation. Is there maybe a blockage in the cooling system circulation?
 
Hi, thanks for your input. I was hoping that it would be the headgasket so that I could start stripping and see how much damage there is. But after today it is inconclusive. The cooling system is fairly new. I have flushed the radiator/heater core several times in the past but I cannot tell if there is such a blockage that would cause this.
 
Hi all,

I am back with some more and I am hoping that someone can shed some light:

1. My sniff tester has finally arrived. I have done the test 4 times and the magic liquid has not changed colour. I have done it when cold, when warm and after taking the car for a short drive and back. There appears to be some fluctuation caused by the air stirring when revving the car but other than that nothing.

2. If I leave the car idling for long enough the coolant will overflow the tank, cap on or off makes no difference. The radiator hoses will begin to harden but not rock hard or buldging.

3. While testing, I noticed that the fan will never kick in. I've done the output test with VCDS and the fans will turn on at all speeds.

4. I have unplugged the coolant temp sensor at the bottom radiator hose so that the fan will stay on continuously. I then left the car idling for about 30 minutes with the coolant cap on and the level remained within limits without overflowing.

5. Can anyone suggest a set of observations in VCDS to help me troubleshoot this? What are the measuring blocks for the temperature and at which point should the fan kick in and what is the telltale block?

Bonus picture:
View attachment 104744
Has the rubber hose to the coolant expansion tank shown in your photo been replaced at all?
 
Hi, thanks for your input. I was hoping that it would be the headgasket so that I could start stripping and see how much damage there is. But after today it is inconclusive. The cooling system is fairly new. I have flushed the radiator/heater core several times in the past but I cannot tell if there is such a blockage that would cause this.

I agree with you... but on the other hand if the pressure is building in the cooling system, there is only one way it can be happening. :(

In my case there was no overheating, no visible smoke from the exhaust, just a slow coolant loss that gradually got worse over time. Unfortunately I did not get a chance to do the combustion fume test from the coolant.
 
Actually that might be the only bit of original hose left on the car!
You probably won't believe it after all that you have done but Ironically that is what I believe solved the leak that was occurring on the fsi I bought to save from being broken, which had a somilar leaking coolant reservoir and suspected head gasket failure, amongst other fsi issues obviously.

When up to temperature and hot, a small amount of coolant was seeping from between the hose and the plastic overflow reservoir tube it connects onto and initially I thought the tube might have a split or crack in it but when I replaced the overflow reservoir it was the same. The thermostat housing and thermostat had also been changed so that was ruled out but then when I swapped the small rubber hose the problem was solved.

Worth a try👍
 
Last edited:
Just to say, my internal temperature gauge always was bang on at 90' and never showed any other signs of over heating, just the coolant leaking from what looked like out of the coolant expansion tank when up to temperature 👍
 
You probably won't believe it after all that you have done but Ironically that is what I believe solved the leak that was occurring on the fsi I bought to save from being broken, which had a somilar leaking coolant reservoir and suspected head gasket failure, amongst other fsi issues obviously.

When up to temperature and hot, a small amount of coolant was seeping from between the hose and the plastic overflow reservoir tube it connects onto and initially I thought the tube might have a split or crack in it but when I replaced the overflow reservoir it was the same. The thermostat housing and thermostat had also been changed so that was ruled out but then when I swapped the small rubber hose the problem was solved.

Worth a try👍
Have you a picture of the area & the hosein question, I think I have the same issue not drastic, but I would like to renew the pipes anyway.
Cheers
 
Have you a picture of the area & the hosein question, I think I have the same issue not drastic, but I would like to renew the pipes anyway.
Cheers
Yes here is a photo.

It's the short angled one that connects onto the coolant expansion tank on the top left from the plastic 'Y' branch.

From memory I think it's marked 'B' but I'm not near the car to check so not 100% certain on that 👍
 

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Yes here is a photo.

It's the short angled one that connects onto the coolant expansion tank on the top left from the plastic 'Y' branch.

From memory I think it's marked 'B' but I'm not near the car to check so not 100% certain on that 👍
Thank you, I have a couple of them.
 
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Hi all,

I just got round to setting up VCDS and having a look at the measuring blocks. Well, well....

I am getting a constant cool 15 degrees at the Radiator outlet from block 130. I thought I'd found the b****r with a failing temp sensor...BUT, when I touched the lower radiator hose it was indeed very cool and that was after the car had reached operating temperature. The lower hose gets hot near the thermostat and colder as it gets near the radiator.

The top hose is hot whereas the bottom is cold. So is it possible that I do have a blocked radiator? Or a failed thermostat even?

Bonus picture:

viber_image_2023-02-18_16-08-36-704.jpg


Evros
 
Hi all,

I just got round to setting up VCDS and having a look at the measuring blocks. Well, well....

I am getting a constant cool 15 degrees at the Radiator outlet from block 130. I thought I'd found the b****r with a failing temp sensor...BUT, when I touched the lower radiator hose it was indeed very cool and that was after the car had reached operating temperature. The lower hose gets hot near the thermostat and colder as it gets near the radiator.

The top hose is hot whereas the bottom is cold. So is it possible that I do have a blocked radiator? Or a failed thermostat even?

Bonus picture:

View attachment 104791

Evros
Because the FSI has two coolant circuits.
One through cylinder head, oil cooler, and heater matrix, which is always open, not thermostat controlled.
The other is engine block etc, and is thermostat controlled.
The fan is controlled by FCM, and will only run if there is too little temperature drop across the radiator. (All electronic, no relays or thermal switches).
The always open circuit is quite good at keeping the engine cool as it's the head that generates most heat.
Both circuits pass through the thermostat housing which acts as a coolant distributor, so it will feel warm, even though the thermostat is closed.
It could be that the thermostat is not opening, but if the temperature at the engine coolant outlet is below 110C, the engine is not overheating, which it would if the thermostat was never opening.
There's a recent thread, where an FSI is overheating, and I believe the thermostat on that car is not opening. The fact that the fan runs, when the ignition is turned off, confirms the overheating is real. His thermostat is definitely not opening.
FSI 'ology is an evolving science 🤔
Mac.
 
Hi Mac,

The car was idling for nearly 35 minutes and if left for any longer the coolant would start overflowing the tank. Obviously an abnormal situation.

The fan should kick but doesn't because as you say the temeprature at the outlet reads a continuous 16 degrees, so in the ECU's binary logic, all is good and it should keep the fan off.

But the hose is cold anyway and the sensor is not malfunctioning so something must be keeping the coolant in the block circuit stationary and not flowing as it should.

Or am I getting something wrong?

Evros
 
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