Originally Posted By: jorton
Can I trust the oil light? If It never comes on during hot idle, or any time, is my old dd's oil pressure ok?
It should come on when you turn on the car but haven't started the engine yet. If not then the bulb or pressure switch isn't working.
It shouldn't come on at hot idle, if it does it should be considered a serious warning. In that situation the light will likely turn off as pressure builds at higher revs but that doesn't mean the pressure is acceptable.
If the light works but never comes on with engine running, it doesn't really prove you have good pressure. The most you can assume from no light is that you probably have good pressure at idle. Above there, you don't know.
The trouble with oil lights is they're driven by a simple switch, not an analog sender, so there's no way for the light to adjust for RPM. The switch triggers below some fixed amount of pressure, like say 8psi. This would be marginal at hot idle but disastrous under load.
Cars with a gauge could possibly use that information to make a smarter oil light, but at that point the light is redundant anyway.
