I forgot to put the coolant cap back on after topping up.

It fell out of the engine bay while driving and is now lost.

I drove 2 x 10km with no coolant cap before noticing.

I did not lose any coolant.

I understand from googling that without the cap for pressure the system can boil when it reaches operating temperature with the loss of a large amount of coolant (and possible overheating damage).

But how far can you typically drive before this temperature is reached if unpressurised coolant is circulating?

I have a new cap ordered but I am wondering if I can still limp around a a bit while I am waiting.

Petrol 2.1 Manual

 

mojorising, what you ask is a relative question. How hard are you on the gas? How warm is it outside? Lots of stop and go traffic? Highway? These are all variables. In short, I would say that driving it at all is a risk. Can you drive 10 KM and be ok, seems so. Did you get lucky? Maybe. Can you do it a third time and be good? Flip a coin. heads you win, tails you lose. I would atleast try to put some sort of heavy duty bag over the opening and then zip tie it in place to try and build up pressure as a safety measure.

 

Thanks Thermo

I have got a new cap ordered so I will wait till it arrives

 

For every pound of pressure, you gain around one degree above boiling point (212F) A 16 pound cap gives you a boiling point of 228F.

Any type of covering as Thermo said is important as you do not want to lose coolant from splashing around.

I drove around town in cool weather with a bad cap that would not hold any pressure without any problems. Go slower, check the coolant level, and be smart.

 

^Thanks Larry