When the engine is off and cold, my coolant level is about 1cm below the min mark, when the engine is warm it reaches about the min mark.

If I open the cap when the engine is cold nothing happens and the level stays below the min mark, however after a drive when I went back to the dealership that sold the car to me with a full service they just unscrewed the cap and when the air released it shot right up to max and they said because the system is sealed and pressurised I don't need to worry and I don't need to top it up.

Silly me assumed they knew more than me because they service these cars all the time so I drove away, but a part of me feels that they might just be trying to fob me off so I am turning to you guys for some honest advice! I always thought the level should be between min and max, otherwise what's the point in the marks? Also the Haynes manual says the same (that the level should be between min and max when cold). Where is the level on your cars? What is the general recommended level?

The coolant is a red/orange colour which I am assuming is the G12 long life original maintenance free coolant. I haven't had any issues with anything so my question is should I top it up or should I just keep an eye on it and live with it as it is? (If it isn't broken, don't fix it and there are definitely no leaks in the system as the level has remained constant.) If you do recommend topping it up, could I just top it up with a bit of tap water as I don't have any coolant? Or would this cause some kind of deterioration or rusting in the system? (obviously the anti-freeze protection would be slightly reduced as well.)

Edited 24 September, 201015 yr by SkodaFabiaOwner

You're correct, it should be between the min and max marks when cold. Just topping it up with water won't cause any harm if it's such a small amount of water, so I'd do that.

The reason it rises when warm is purely due to the coolant and water expanding as they get hotter - hence why you should check it whilst cold.

Just top it up to the maximum mark with water whilst the engine is cold, then check it now and again to make sure it isn't leaking away anywhere.

Definitely do not top up with just water, as eventually you'll just put a little bit more tap water in there and a little more then you won't know what dilution you have any more My preference would be for appropriate coolant (g12, g12+, g12++, VW TL 774d (same as g12 I think), VW TL 774f (g12+) or VW TL 774g (g12++ I think). The VW TL 774d is available from Halfords as their advanced 5 year coolant, but is quite expensive without a trade card. Otherwise G12++ should be under £10 for a 1.5 litre bottle at GSF or any Skoda, VW, Audi, Seat dealers. I would mix this 50/50 dilution with deionised water personally, although with the additives in the coolant, tap water would probably be fine.

I believe official word is coolant level should be at max when warm and when cold should be somewhere between min and max. TBH I doubt you'd have any issues topping it up to the max mark when cold.

Whatever you do do NOT add any other types of coolant, particularly blue stuff to the G12 already in there as it does not react well (makes a murky gel stuff which would take some effort to clean out properly).

I don't understand why the level shoots up when you remove the cap when warm. Mine does it also even to the extend of overflowing, and tends to overflow like mad if run with the cap off when the fan cuts in. I thought the overflowing was a sign of a defect on my cooling system. All I can guess is that it's designed to work that way as the cap is meant to release pressure in the cooling system up to a predefined pressure level. I guess the way to look at it though is if everything is as it should be, the car runs fine, and there's no overheating then it's probably best to leave it be.

Thanks very much for both of your replies, at least you've put my mind at rest!

I was considering just topping up with water, but as I am so much lower than the maximum mark (probably by about 1 litre) I think I am going to get the proper Skoda G12 stuff as apparently this doesn't need changing and the Halfords stuff either has a 2 or 5 year maximum life.

I will probably just use the whole bottle and not add any water so hopefully my anti-freeze protection should be upped for winter as well...

Definitely do not top up with just water, as eventually you'll just put a little bit more tap water in there and a little more then you won't know what dilution you have any more

You could always just buy something like this to check:

Anitfreeze Tester

I believe official word is coolant level should be at max when warm and when cold should be somewhere between min and max. TBH I doubt you'd have any issues topping it up to the max mark when cold.

It's fine to fill it to max, as long as it's cold when doing so. See these snippets from the Fabia handbook for confirmation:

I don't understand why the level shoots up when you remove the cap when warm. Mine does it also even to the extend of overflowing, and tends to overflow like mad if run with the cap off when the fan cuts in. I thought the overflowing was a sign of a defect on my cooling system. All I can guess is that it's designed to work that way as the cap is meant to release pressure in the cooling system up to a predefined pressure level. I guess the way to look at it though is if everything is as it should be, the car runs fine, and there's no overheating then it's probably best to leave it be.

The reason it doesn't boil over when the cap is on is due to enthalpy - the pressure in the system allows the coolant mixture to reach a higher temperature before it boils. For example, we all know that water boils at 100˚C, but in reality this is only when the pressure is at 1 bar, or atmospheric pressure. Looking here, it can be seen that at 1.3 bar, the boiling point rises to 107˚C.

That therefore explains why it boils over when the cap is removed - the pressure in the system is released, but the coolant is still at the temperature over 100˚C - it therefore boils over.

I hope that doesn't sound patronising at all, as it wasn't meant to be - just an explanation of why it happens, that's all.

I was considering just topping up with water, but as I am so much lower than the maximum mark (probably by about 1 litre) I think I am going to get the proper Skoda G12 stuff

If it's that low, then yes, I'd recommend topping up with coolant as well as water.

as apparently this doesn't need changing and the Halfords stuff either has a 2 or 5 year maximum life.

According to the service guide, G12 needs changing every 5 years as well.

I will probably just use the whole bottle and not add any water so hopefully my anti-freeze protection should be upped for winter as well...

Make sure you mix it properly - there is a reason that the manufacturers recommend mixing it with water rather that putting it in neat. Try your best to ensure you have a healthy coolant mixture, by all means, but don't just dump the coolant in there.

I hope that doesn't sound patronising at all, as it wasn't meant to be - just an explanation of why it happens, that's all.

Not at all, thanks very much for explaining those points I guess this is why the service manual states to put the coolant cap on before running the engine in order to bleed the system. I'm used to the concept of running the engine with the cap off to help remove any air locks.

According to the service guide, G12 needs changing every 5 years as well.

The car manufacturers seem to have rather strange ideas when it comes to "filled for life". So long as it meets the appropriate specs it should be ok. I guess they expect something to need changing to necessitate coolant renewal within about 10 years, or that by that time the car is scrap fodder anyway (sad but true).

Edited 24 September, 201015 yr by anewman