Bad Radiator Cap

Yep.

I had to replace mine a few years back. It was leaking around the edge.

Just picked up a simple replacement cap.

Every oil change is a bit absurd unless you leave your oil in for a loooong time.

Most radiator shops, general repair shops, will pressure test your cap for you for free. Some places require this as part of smog testing.

In point of fact, shortly after shutdown is the most likely time for something to blow. Engine is still hot - hotter than coolant by far - and nothing is circulating so temp goes up by quite a bit for a few minutes. Most times, the result is an overflow from the overflow bottle unless you have one of those closed systems.

Cap failure is a common thing - usually shows up as overheating due to the slow loss of coolant. Just be glad that it's a cheap fix! When I see a puddle after shutdown it usually signals that the pressure has popped the shaft seal in the water pump.

Thanks for that info...

Larry