Mark Belanger wrote:

> I had an old Honda that would do this when I was low on oil.  Don't ask
> me why, as I thought oil idiot lights were based on pressure, not level.

They are.  But when the level gets low, if you do something that sloshes
the oil around in the pan, like stomping on the brakes or hammering a
hard corner, the oil pump pickup can be uncovered and start sucking air.
 This causes a pressure drop that can turn on the light.

On at least one car I've seen, you could actually see the oil pressure
varying rapidly up and down on the gauge as the pump intermittently
pulled air, when the level got low.  Topping off the oil would bring it
back to rock-steady pressure affected only by engine RPM.

Some cars use a pickup on an arm that can swing in an attempt to help
prevent this problem, the theory being that inertia will swing it to the
same side of the pan that the oil's sloshing towards.

On VW boxer engines the problem is especially acute because if you
corner hard enough, you can send the oil clear out of the crankcase and
up into the head via the pushrod tubes. ;)