Polo 9n tdi - pressure in coolant system

[Jazzy K 25]

Good day All,

I am new to the forum .

i have being having a issue with loss of water in the cooling system ,which comes out of the coolant overflow when at high speeds.

I have replaced the thermostat ,overflow cap (Agents ),water pump is working fine ,coolant temp sensor,thermo switch for the fan .
i have taken the car to silverton for a pressure test , results : colour didnt change and pressure builds up with no loss of pressure.
I have asked around no one seems to point me in the right direction as i do not want to tamper with the head when it could be somethings else.

Please if any one could assist me and point me in the right direction .

[mpkhotha]

Hi did you bleed the air out? It might be an airlock...

[Jazzy K 25]

Hi yes I did bleed the system

[mpkhotha]

1. Open the overflow cap.
2. Trace the upper small hose from the overflow tank..it connects to the upper inlet hose of the radiator and has a small clamp. Unclamp it at the radiator inlet hose and blow air into it...it tends to build up a blockage and cause overheating and other problems. If blocked, try to unblock it, clamp back everything and test.

[Callum229]

Hi

I had the same symptoms, it turned out that it was the head that got corroded and was leaking combustion gases through the coolant and then pressurizing the coolant system then eventually blowing out the cap.

At idle, and during low load, there was no loss of coolant, eventually it got worse and I replaced everything besides the head gasket(yes it was A LOT OF MONEY).

Symptoms of the head gasket blown that I documented are

- Coolant pushing out the bottle
- Heater goes cold when you rev the car or when on the freeway
- Bottle has signs of corrosion(rust) and coolant is not the purple or pink coolant that is supposed to be used.
- Sometimes I would notice that the coolant on the overflow pipe that goes on the top of the coolant bottle tends to reduce the steady flow it has and start producing bubbles.
- Car will overheat when going uphill

Check this youtube video of what destruction the wrong coolant caused.

https://www.youtube.com/watch?v=9YZraNpGd4A

In my case, because of the corrosion, the head had to be replaced(didn't want to weld the ports up and then have a blown head gasket), water pump, radiator, oil cooler, trans cooler, etc.

For more in-depth symptoms, check my posts on my profile where I described exactly what was going on, trying to figure out the problem.

After replacing the head gasket, did over 10 000kms, not a single issue.

Hoping that it is just a blown head gasket or something simple!