Possible head gasket on 2.0 tdi

[pmmcbl]

Hello all. On the other day I had what I believe steam coming from the exhuast when the engine was at full temperature. I had a quick look and someone else wrote the same thing and it was mentioned it could be fuel contamination. It was possible and my car does sit around for weeks without being used.

The steam only happened 3 times within 3 minutes and ever since nothing. But I started thinking, it's also a sign of early stages of a head gasket failure.

My question is. If it's a head gasket it would for sure let steam out all the time? The coolant level hasn't moved either.
I wasn't aware of head gaskets going on the 2.0 tdi common rail reason why I didn't think of it.

Thanks