SurferTim:
Datasheet.
http://www.ti.com/lit/ds/symlink/lmv358.pdf
Max voltage any input = 5.5v
That means 11v is the upper limit to Vin without overdriving the op-amp.
Well the op-amp has internal clamping diodes applied to the input pins to prevent the pin voltage from exceeding Vcc + diode voltage drop, so hence the 5.5vdc rating. However as the current flow is limited by the resistance of the voltage divider the 'clamping diode fault current' (what .4 ma at vin=20v?) thus generated may be fine working in this matter. That is not unlike how much higher voltages then Vcc can be applied to a AVR input pin if it's in wired in series with a high enough resistance to limit the diode clamping current to a safe value. However, I can't find a specification in that datasheet that states the maximum safe input clamping diode forward current rating. However I feet it's pretty safe that running Vin up to the 20v max rating does not subject the op-amp to any damage because of a combination of the internal clamping diode and the series resistance of the voltage divider. I think clamping current at under 1ma is most likely 'safe' for the op-amp.
Anyone know more about this?
Edit: A on-semiconductor datasheet for this device type gives a specification called
Maximum Input Current 10 mA
Which would mean that .4ma of clamping diode current when Vin is at 20vdc or less would be fine.
Lefty