My 2013 Octavia 1.6 diesel intermittently emits steam from under the bonnet. Sometimes great clouds, other times barely noticeable. I first noticed it about 2 weeks ago, there is no signs of the engine overheating and I haven't lost any coolant. It smells like overheating coolant but as I say, there is no loss from the header tank. I'm wondering if it could be some leak from the windscreen washer reservoir but cant see how that would get near the exhaust or other hot engine components. Has anyone else come across this?

Maybe a failed expansion tank cap. It doesnt take much water/coolant to make a lot of steam so you may not be noticing it drop. Not sure where the expansion tank vent hose goes. It could be near exhaust etc. Mark the tank level when cold and check after a day or two when cold. Doubt its the washer fluid as its low down near front.

7 minutes ago, Alasdair1 said:

Maybe a failed expansion tank cap. It doesnt take much water/coolant to make a lot of steam so you may not be noticing it drop. Not sure where the expansion tank vent hose goes. It could be near exhaust etc. Mark the tank level when cold and check after a day or two when cold. Doubt its the washer fluid as its low down near front.

Thanks Alasdair, you may well be correct. I'll try that.

Had loss of coolant on an old toyota and couldn't work it out. Not much at all but tank level would drop very slowly over a week or two. Couldn't find any noticeable leaks so I tied a plastic juice bottle onto end of expansion tank hose and after a day or two it had some coolant in it. Car wasn't over heating either. New cap and it was sorted.

Alasdair

I'll keep an eye on the coolant, I've marked the tank so will be able to tell if it has dropped.