[Skulemate]

Not that anyone's going to use it, but I still want to point out that using a fluid that heavier than water will have an impact on a pumps performance, even if you disregard differing viscosities. The reason is that a column of mercury is going to create (if memory serves) 13.55 times more pressure than a column of water the exact same height... that's why it's often used as a manometer fluid, since you don't need redicuously high tubes in order to work with higher pressures. My pump manufacturer specifically states not to pump any fluid with a specific gravity of more than 1.1 to boot.