Mk3 Leon Fr 5 door 2016. Leaking coolant after time belt changed

[Leon1611]

Hey everyone. I got this car in June 2021 and was running 100% until the coolant light started coming on around January time. Coolant tank was empty to kept it filled and the light would only come on mayne once every week or 2. This increased to almost daily until one day the water pump went and the car wouldn't hold any more coolant. Got this changed last month and the car has been running grand apart from the light still comes on and I can see the coolant under the car when it has been parked. I've checked the oil cap and dip stick and don't see any milkyness.
I can hear the radiator after the car has stopped and it sounds like sloshing/ bubbles. There's no issue with the heating and its working fine on both sides.

Could this be the coolant tank? Is it usually expensive to get the coolant system pressure checked? I assume this would be checked when the timing belt was changed.

Any advice is much appreciated

 

[black_sheep]

I had a similar issue to you on my 184 ps Octavia VRS. Had the car pressure tested and within 200 miles the water pump failed catastrophically.

Was the belt replaced after the water pump failed? It should have been as the coolant can contaminate the belt.

Even after the water pump and belt were replaced, I kept losing coolant. The car was traded in prior to the heater matrix issue being identified as the likely root cause, with the system over pressurising and dumping coolant from the expansion tank. The car was still pumping out some heat via the vents, albeit nowhere near a fully functioning system.

Prior to changing the heater matrix I would check that all of the coolant hoses are securely connected and that there is no damage from the repairs. The hoses sometimes get small pin hole leaks, which open up when the system is warm/under pressure.

There are UV dye kits that you can use with coolant to aid leak checking.

 

[Leon1611]

Thanks for the reply. Yeah the waterpump and timing belt were changed at the same time. Heaters are working the same as they always did. What is the best way to use the dye kit?
Hoping it's nothing too expensive if possible.

I had a similar issue to you on my 184 ps Octavia VRS. Had the car pressure tested and within 200 miles the water pump failed catastrophically.

Was the belt replaced after the water pump failed? It should have been as the coolant can contaminate the belt.

Even after the water pump and belt were replaced, I kept losing coolant. The car was traded in prior to the heater matrix issue being identified as the likely root cause, with the system over pressurising and dumping coolant from the expansion tank. The car was still pumping out some heat via the vents, albeit nowhere near a fully functioning system.

Prior to changing the heater matrix I would check that all of the coolant hoses are securely connected and that there is no damage from the repairs. The hoses sometimes get small pin hole leaks, which open up when the system is warm/under pressure.

There are UV dye kits that you can use with coolant to aid leak checking.

 

[SuperV8]

Thanks for the reply. Yeah the waterpump and timing belt were changed at the same time. Heaters are working the same as they always did. What is the best way to use the dye kit?
Hoping it's nothing too expensive if possible.

I tested my header tank cap and found it to be leaking at something like half its rated pressure, so they can fail and are a cheap replacement to try if you are having leaks.

 

[Leon1611]

I tested my header tank cap and found it to be leaking at something like half its rated pressure, so they can fail and are a cheap replacement to try if you are having leaks.

I've replaced the cap already, was the first thing I changed

 

[SuperV8]

I've replaced the cap already, was the first thing I changed

You didn't mention this, just that "could this be the coolant tank"

I would first find out exactly where it's leaking from?

 

[black_sheep]

Type: ‘uv dye leak coolant’ into a search engine and you will see a number for sale on a shopping channel of your choice.

The Ring version with a UV torch and dye is not too badly priced.

Before adding the dye, use the UV torch to check the engine bay first, in case a previous owner has used it and it’s now already all over the engine bay after the water pump failure. You should only need 1/2 a bottle of the dye, and wash off as much as possible once you have identified the leak.