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

Evripidis

Member
Hi all,

Calling the knowledgeable folk of this forum. This is not strictly an A2-related question but it relates to internal combustion engines in general.

Is it possible to have a head gasket issue, i.e., pressure build-up in the coolant without any other of the usual symptoms? I get coolant out of the vent hole. I also have a minor leak from the thermostat housing but I am guessing that this is due to the o-ring that I haven't been able to replace when I took it out. The cap is brand new too. So am I right thinking that this might actually be a damaged head gasket and I am in a Trigger's broom situation trying to fix issues that are ultimately attributed to a higher-than-usual coolant pressure?

Fuel economy is a constant 46-47 MPG and performance is great. No white smoke, emulsification or changes in the level or colour of the oil/coolant. Compression tests are consistent with maybe some blow-by.

Regards,
Evros
 
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Is it possible to have a head gasket issue, i.e., pressure build-up in the coolant without any other of the usual symptoms? I get coolant out of the vent hole?

Yes, this engine has an operating temperature around 105 degrees Celsius which means that it also runs at overpressure. Any leak will lead to boiling coolant fluid.
My Fsi had a broken O-ring in the coolant cap which led to the same owerflow as yours.
 
So to preclude any headgasket damage, I would have to rectify the minor leak at the housing, correct? This would keep the pressure high enough in the system so that my G12+ won't boil. I replaced the cap last week at which point the housing leak became more prevalent.
 
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If the housing is leaking now, it will only get worse in the future. For me it started as a minor leak, but when it was replaced, the plastic was disintegrating. Replacing the housing has the benefit of making it much easier to replace the 'death pipe' behind the engine as well, since it will just pull out from the water pump end.
 
Ευριπίδη γειά εγώ έχω το 1400 με τα 75 άλογα έχω παίξει στα προβλήματα
Φιάχνω πληρώνω φιάχνω πληρώνω
Ατελείωτες ώρες στο you tube και τα αποτελέσματα σχεδόν τίποτα
Μεταξύ των προβλημάτων είναι και η απώλεια ψυκτικου υγρού
Βάζω συνέχεια υγρό στο δοχείο διαστολής
Άλλαξα όλο το κύκλωμα ψύξης εκτός από το ψυγείο και την αντλία
Πέτυχα να βάζω υγρό μία φορά τη βδομάδα τώρα το παρακολουθώ
Δεν υπάρχουν διαρροές και υποπτεύομαι ότι έχει αρπάξει η φλατζα κεφαλής
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Αυτά
Δημήτρης

Στάλθηκε από το SM-J530F μου χρησιμοποιώντας Tapatalk
 
Is it possible to have a head gasket issue, i.e., pressure build-up in the coolant without any other of the usual symptoms? I get coolant out of the vent hole?

Yes, this engine has an operating temperature around 105 degrees Celsius which means that it also runs at overpressure. Any leak will lead to boiling coolant fluid.
My Fsi had a broken O-ring in the coolant cap which led to the same owerflow as yours.

After having fixed the housing leaks as per my last post this appears to have resulted in keeping all the coolant in.

I have also replaced the exhaust gas temperature sensor that appeats to have had a positive effect in keeping the blokc temperaures at bay.

Evros
 
Is it possible to have a head gasket issue, i.e., pressure build-up in the coolant without any other of the usual symptoms? I get coolant out of the vent hole?

Yes, this engine has an operating temperature around 105 degrees Celsius which means that it also runs at overpressure. Any leak will lead to boiling coolant fluid.
My Fsi had a broken O-ring in the coolant cap which led to the same owerflow as yours.

I keep reading that because the FSI runs at a higher temperature, the system is also running at a higher pressure, to prevent the coolant boiling.
I'd not thought about it until now
I believe water expands by 0.000208 % per deg C rise, coolant consisting of a mix of water and antifreeze will be different, but, just guessing, not by much, maybe even lower.
So the difference in expansion of the coolant, (water/antifreeze mix), in an FSI running at 110 deg C and a car running at the more normal 90 deg C will be 0.00416 %, again, not much.
Coolant consisting of water, and antifreeze, has a boiling point of well over 120 C, so will not boil in either engine, (under normal conditions).
If this is broadly correct, (and it may well be rubbish), the pressure in either engine will not be much different.
I'm sure there are members who understand the physics of this, so is my thinking totally duff, or not far out?
Mac.
 
I had to do a similar study for the solar hot water thermosiphon at my house for calculating the expansion tank volume. For the a2 we know what the coolant system volume is and the amount of expansion that the tank wil allow and also that the system must be tested at 1.2 bar as per elsawin. We can do the calculations for water and get a lower bound. I also assume that the peak temperature at some points of the cooling system will be higher than average for example the housing.
 
I had to do a similar study for the solar hot water thermosiphon at my house for calculating the expansion tank volume. For the a2 we know what the coolant system volume is and the amount of expansion that the tank wil allow and also that the system must be tested at 1.2 bar as per elsawin. We can do the calculations for water and get a lower bound. I also assume that the peak temperature at some points of the cooling system will be higher than average for example the housing.
I'd think it best to assume 120 deg C Max.
What set me thinking about pressure, was the relation that the coolant didn't need to be pressurised to not boil.
So was wondering if the pressure in the FSI was significantly higher than normal engines. We know it runs hotter, and so the assumption is that the pressure is higher too, There should be no air in the system, so expansion of the water is one factor, but I couldn't figure out what actually causes the pressure to rise in a coolant system, any coolant system, not just an FSI.
I'm sure it's obvious.
Mac.
 
Well, I am sad to say that after a 40-mile round trip coolant appears to have escaped the epxansion tank once more.

Evrything else is water tight aside from one jubilee clip maybe that must have leaked 3-4 drops at most.

This car must have a crack in the block somewhere I cannot explain it otherwise. I get 45 mpg out of it and pulls quite good though.

Evros
 
Can you refill the coolant and ensure the cap is a tight fit on the expansion tank. Seal the expansion tank inside a large clear plastic bag and ensure no leaks around the pipes. Drive the car and check to see if the coolant has escaped the tank. If no coolant in the tank and nothing in the bag you can rule that area out. Try to do similar on other areas of the coolant system. A tiny pin hole in a hose or plastic fitting is enough. If tank still empty and nothing caught in bags then possibly the block is cracked.
 
The bay is bone dry. In 46 miles it has lost maybe 3-5ml of coolant only visible around the lip of the tank and nowhere else. All the usual plastic components are less than a year old.
 
The bay is bone dry. In 46 miles it has lost maybe 3-5ml of coolant only visible around the lip of the tank and nowhere else. All the usual plastic components are less than a year old.
I can't see an FSI doing 45 mpg with a cracked block.
Mac.
 
I can't see an FSI doing 45 mpg with a cracked block.
Mac.

I am beginning to investigate the following:

1. The expansion tank is not level (I must be going mad).
2. The heat soak is that bad that the coolant boils over after the ignition has been switched off and the fans have turned off (I might fabricate a pulse extender on a piece of veroboard so that the fans stay on a while longer).

I have just finished a 20 mile trip and checked it while it was still hot (43 degrees ambient continuous over here for days). Not a drop to be found anywhere accept from a slight smear around the lip of the expansion tank.

Evros
 
I am beginning to investigate the following:

1. The expansion tank is not level (I must be going mad).
2. The heat soak is that bad that the coolant boils over after the ignition has been switched off and the fans have turned off (I might fabricate a pulse extender on a piece of veroboard so that the fans stay on a while longer).

I have just finished a 20 mile trip and checked it while it was still hot (43 degrees ambient continuous over here for days). Not a drop to be found anywhere accept from a slight smear around the lip of the expansion tank.

Evros
Just thinking aloud, but the coolant should not boil, even if the engine is not running. The pressure in the system, and the increase in boiling point provided by the antifreeze will prevent this, so you must be loosing pressure, and with no fluid leaks, could it be air loss via the cap.
If the weather temperatures stay high, maybe consider an electric after run pump in Upper circulation circuit, head, heater matrix etc, which is always open, to dissipate some heat
The TT has this, and it runs for 10 minutes, triggered by the ignition being turned off.
Mac.
 
It is too brand new. I have two extra ones in their packaging. Maybe the expansion tank has worn. It was a second hand anyway. The seal on it is tight though. I ll try and get a new one. I might be able to get one off a different model and make it fit.
 
It is too brand new. I have two extra ones in their packaging. Maybe the expansion tank has worn. It was a second hand anyway. The seal on it is tight though. I ll try and get a new one. I might be able to get one off a different model and make it fit.
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.
 
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