1.9D DW8 Forgot to put coolant cap on, and drove for about 2 hours. Any risk?

[kenbw2]

Checked my coolant level last night, then drove home - about 2 hours on the motorway at 50mph. Temp gauge was exactly where it should be all the way.

Come to refill my washer bottle, and noticed I'd forgotten to put the cap back on.

Coolant level is exactly where I left it last night so it's not boiled away thankfully.

I'm worried it might have affected the coolant's ability to circulate, and maybe caused some localised heating, critically around the head.

What thinks you?

Is there something I should do, or just sit and hope I've got away with it?

[dnsey]

I'd say that it's very unlikely to have done any harm. The pressure cap simply allows the coolant to get hotter without boiling, and doesn't affect the circulation - on most modern engines it's fitted to the resevoir anyway, so is not even directly associated with the actual cooling system.
I've driven miles before now with a loose cap to minimise the loss from a leaking rad, with no ill effects.

[Homer]

If it didn't boil over and blow all the water out then it will be fine. The cap is mainly there to allow the pressure to increase which raises the boiling point of the water slightly.

[Peter.N.]

It will only boil if you thrash it, driven normally it should be OK. I ran an XM with the cap loose for several years as the head gasket was leaking and it was blowing the water out, with the cap loose didn't loose any as it was relieving the pressure in the cooling system, but of course the success of this arrangement depends on how badly the gasket is leaking.

Peter