I have a Skoda Octavia 2.0 FSi which appears to have a very strange coolant leak.

I first noticed in December 2008 where the coolant level dropped from the maximum level to minimum level in a period of a week. At present (hot summer weather) in drops from maximum level to minimum level over a period of 3 to 4 weeks. I have topped the cooling system up with just over 3 litres of 50/50 G12++ coolant and distilled water between December 2008 and July 2009.

In cooler weather there appears to be clouds of white smoke / mist from the exhaust pipe – this is not so apparent in hotter weather. Occasionally there has been funny condensation of the windscreen with a sweet smell inside the car but this has only occured 3 or 4 times since December 2009.

No damp patches have been found in the passenger footwell (suggestive of heating matrix issue). Brief smell of coolant in cabin has been observed about three times since December 2008 but only while car has been warming up.

The temperature gauge on the dash board has never indicated any overheating – the temperature has never gone above 90 degrees centigrade.

It has been taken into my local dealer a couple of times for pressure testing and they have identified no leaks although they did replace the EGR valve back in February 2009, although it still currently leaks coolant.

I have been trying to get the original dealer to identify and fix the issue before the warranty expires in a couple of months time (they have known about it since december 2008) although they keep informing me that as they cannot identify an issue they cannot make any repairs.

I have been in contact with a couple of independant mechanics who said that they beleive it could be an internal leak (head gasket failure or crack in engine / cylinder head block) but will need to do a block test on the engine which they will charge around £50 for (which would not be covered under warranty). A respected mechanical engineer that I know has also provided the same feedback.

The original dealer have said they have already done a block test, pressure test and exhaust emissions test and have found no faults. They have passed it onto the Skoda technical team, which is part of the warranty department at Skoda, who basically said that as the dealer could not find any faults there can not be any faults with the car. I have even supplied a list of symptoms to both the dealer and warranty department with digital photos clearly showing coolant going down in the expansion tank (all taken when the engine had cooled overnight).

Would anyone have an idea of what these symptoms could be an indication of and what action needs to be taken to confirm the diagnosis?

Also would anyone know how we can get the issue fixed under warranty seeing as the warranty company and dealer cannot diagnose the issue at present?

White smoke (steam) when the engine is warmed up is a sure sign that there is water getting into the combustion chamber. This is most likely to cylinder head gasket leak or internal crack - i have had both on older cars i've owned in the distant past (neither were Skodas).

I would pay the £50 to get the the block test done independently. If that comes back showing a fault then you have a powerful arguement for getting the (expensive) repairs done under warranty.

Hope you get it sorted!

Don't be tempted to crack an egg in the coolant tank or use any of that other stuff you can buy for fixing leaks on the cooling system.