Proximity sensor for humid and high heat enviroment.

I would like a sensor that can withstand liquid and high heat (100C) but so far I have found nothing.
At first I thought about using a ultrasonic distance sensor with waterproof sensors, but it seems they are only rated for 85
C. (but they would be perfect if not for the temperature rating)
I would like to stay away from mechanical switches as they might gum up and fail on me.

I would use it to measure liquid level.
Or more precisely I want the sensor to turn off a pump once a certain level is reached.

Any suggestions?