I serviced my car the other week, I was in my garage (as it has a pit) where my mum keeps her mini.
Was in there most of the day, and towards around 530 I was sort of rushing in order to get out of there before my mum got home so she could get the mini in there.
I checked the brake fluid, fine.
Checked the coolant, could do with a top up!
All done I cleared up and got out just in time.
Went for a drive later, waiting outside a mates house I see smoke coming from the engine bay.
"Must be oil that I carelessly spilled down the engine block when I was filling it up, just burning off from a hot engine" I says to a mate.
Engine off, out the car and bonnet open and there's the coolant expansion tank erupting like Mt. Vesuvius!
It had puked its guts up all down the road

I'd only forgotten to put the expansion tank cap back on! :embarassed: :embarassed: :embarassed:
So there we are running in and out of his house with kettles full of hot water to fill it back up again, bloody hurt squeezing the radiator tubes to get bubbles out of the system!
Luckily I hadn't lost the cap, it was in the battery tray!