Ever heard the saying, "Water and electricity don't mix?" Though it obviously hints at the dangers faced when using electric appliances near a source of H2O, the learned amongst us know the truth behind this saying is actually a little more complex. (That is, while pure "distilled" water is not a particularly good conductor, adding anything to make a solution increases conductivity dramatically.)
Sneer at this loose analogy all you want, but such a multifaceted truth applies to the use of electric water pumps in automobiles. These items have become a popular upgrade for late-model Corvettes, said to offer some of the same benefits as time-honored bolt-ons such as cold-air intakes and converter-back exhaust systems (namely, increased horsepower along with easy installation). But many readers have probably been thinking, "What exactly does an electric water pump do, and is it right for me?"
We at VETTE are here to shed some light on the benefits and drawbacks of these devices, and we've lined up Meziere Enterprises, one of the largest manufacturers of water pumps of all kinds in the U.S., to lend us a hand.
From a physics and engineering standpoint, let's look at the differences between an electric and a mechanical water pump, as used on an internal-combustion engine. Just to dispel any possible confusion, electric pumps don't ionize, "electrify," or change the properties of the coolant they pump. Rather, it is their flow rates-and the amount of energy it takes to achieve these flow rates-that makes the difference between them and the conventional mechanical pumps fitted to nearly all cars and trucks on the road.
Think of a mechanical water pump as a slave to the engine: The speed at which its impeller turns is always proportional to engine rpm. The Meziere brothers (Dave, Mike, and Don), owners of Meziere Enterprises, know all too well that the design of any mechanical water pump is a series of compromises.
"It is difficult to design a mechanical pump that works well at both the high- and low-rpm ends of the spectrum," says Don Meziere. "A larger impeller with tighter clearances is going to move a lot of water down low, but once you start to turn fast, it's going to take a lot of horsepower to turn, and it's also going to begin to cavitate."
Though the term sounds like what happens to your teeth when you eat too many sweets, cavitation is a phenomenon in fluid mechanics. In a nutshell, it occurs when a flowing liquid subjected to certain types of motion transforms to its vapor state (in other words, boils-not because of high temperature, but because of low pressure). This gives rise to vapor bubbles within the coolant, which subsequently collapse. This is bad news. In addition to reducing the efficiency of the pump, the pressure waves created when the vapor bubbles change back to liquid can also cause pump-parts breakage.
According to Meziere, "Simply put, this separates the coolant and stalls out the flow in the system, greatly diminishing its capacity to cool the engine. The impeller turns so fast that the water can't get down the high-pressure [outlet] passages and starts to swirl inside the impeller chamber. It creates 'air' in the system, so to speak, though this gas is actually coolant vapor."