Hello!

My beloved Skoda Octavia, mk3, CKFC, 2.0 TDi is magically loosing coolant.

Water pump has been changed about 80.000km ago, as well as head gasket. And recently coolant started to disappear with a rate 1.5-2 dcL/1000km.

No visible coolant loose, no check engine light, no white or blue smoke. So assumption was made that EGR heat exchange must be faulty. As well as valve and head exchanger were replace - coolant disappearing continues. We proceeded with chemical test of CO2 presence in coolant was made. No, CO2 in coolant was detected.

Footwell area sims to be dry. No visible marks of coolant. As well as engine radiator. Also no crack on coolant expansion tank or its cap.

We have runed out of ideas. what could be a problem. Any ideas anyone? Did you maybe encounter similar problem? What was the solution?

Thank you for an answers, responds.

Edited 23 September, 202523 Sep by tetoon

2 minutes ago, tetoon said:

No it wasn't.

How do you know?

2 minutes ago, tetoon said:

1.5-2 dcL/1000km

That doesn't seem like much. How are you measuring it?

Is it just being overfilled?

Maybe the cap is leaking a bit out the overflow

How do i know what? That EGR heat exchanger isn't the cause? We replaced it but fault is still present.

For 10 years there wasn't a single mL of coolant loose. So from my point of view every dcL of coolant meas a big difference.

How do i measure it? Fill it up, mark km counter and after 10-20days - when i check fluid level and fill it up, I also check what distance was made.

Cap? How to detect cap leaking? No residue of coolant around.

On 23/09/2025 at 20:45, tetoon said:

as well as head gasket.

Why was head gasket replaced?

Maybe it has failed again but not catastrophically

On 23/09/2025 at 21:35, tetoon said:

How to detect cap leaking? No residue of coolant around.

Look around the overflow pipe. I think it leads out under the coolant tank

Make sense

On 23/09/2025 at 13:49, BlueWagon said:

How do you know?

That doesn't seem like much. How are you measuring it?

Is it just being overfilled?

Maybe the cap is leaking a bit out the overflow

Am adding MIN-MAX level (0.3L) each year and for me those are 22'000km. So, up to 0.2L/1000km seems a lot.

The coolant does not need to be at MAX. At services it might get filled to MAX then after a run the coolant sets it's level between MIN & MAX. If there was a FILL TO THIS LEVEL, that would be marked on the bottle. If the level does not stay steady and drops to MIN then that is an issue / problem.