Really, I shouldn't say that either. The reason why I don't like centrifugal pumps is, they typically turn too fast to allow more viscous fluids to flow into them as they run, the larger the pump the less this becomes a problem. Their pressure is limited by the SPEED and diameter of the rotor, and rely on high rpms to build high pressures, see my previous point about high rpms. They typically will not self prime very well at all, and typically require the impeller to be totally full before they will self sustain. Once the impeller pulls a vacuum enough to cause cavitation they simply stop pumping. This is what causes the smaller pumps to be especially ill suited to pumping oil because the oil cannot fill the impeller fast enough to keep the flow going. There are many impellor pumps capable of fairly high pressures, they typically are expensive or operate at very high rpms if they have small rotors.
I have tried a 1/2" 500GPH impeller pump that wouldn't move oil at all.
A 3/4" 800GPH pump that would move about 2 or 3 GPH of oil.
And a 2" impeller pump that would move oil faster than you would want it to unless you are moving 1000's of gallons. It's head pressure is ok, but it's be ridiculous to try and use it for anything except for moving hundreds to thousands of gallons of oil.
They are extremely efficient oil/water mixers, so if you want them to mix separated oil and water they are extremely efficient at that lol.
I find them acceptable only for rapid transfer of large amounts of oil, BUT I have been tempted to purchase a 1" gas powered on to pack into my oil recovery trailer. Notice I only said tempted... They have thier place, but not in my shed... well that excludes the 2" that I never intended to use for oil, but my cousin demanded it and was giving me over 1000 gallons of oil so I didn't argue.