Water Pump 101: What's Really Going On With The Water Inside ...

When Larson and I were deciding on parts for the World’s Quickest Street Car, the S10 pickup we took on Drag Week, we had to put some serious thought not only into making it fast, but more importantly making it reliable. And as we’ve all experienced, there is nothing more annoying than driving your hot rod and staring at the temp gauge every waking moment because you aren’t sure it will stay cool. A good radiator, water pump, and cooling fans are key, but how do you decide on which ones you need? After all, there are tons of options from just as many manufacturers. Radiators and fans tend to be chosen based on available space, but what about the water pump? Normal questions everyone asks are; Mechanical or Electric? Engine mounted or remote? How big should the inlets and outlets be?, just to name a few. We’re going to give you all the information we can right here to help you choose the right parts for your project, whether it’s a + horsepower beast like our Proline Racing Engines powered S10, a 350 horsepower hot rod, or something in between.

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By nature hot rodders are gauge watchers, but doing so out of the fear of failure is not a comforting position to be in, which is why we were very particular when choosing cooling system components. Especially because we were dealing with some “interesting” challenges in our Brodix PB combo. But more on that later. First off, lets cover some of the basics.

When we were making our decision on who to use for our water pump system, we went to visit the guys at Meziere. Don and crew are the best in the business, and told us when we were right about our assumptions, and were also happy to point out our “misconceptions” when needed. Together we put together a very cool, pun intended, system that worked flawlessly on Drag Week, despite some of those aforementioned challenges. So when it was time to put this story together I sent Don an with about a million questions and clarifications, to put together what we hope will give you a head start on choosing a cooling system for your ride.

What does a water pump do?

Sounds like a simple question, right? But is there more to it than just moving water? Primarily no. Moving water through the engine and cooling system is the primary task of your engine’s water pump. Automotive water pumps are centrifugal pumps and have flow and pressure characteristics that are far different than, say, an oil pump. In an oiling system, pressure is critical, or else you burn up bearings and parts. Oil pressure is determined and maintained by both flow and clearances within the engine, the later being very closely measured and controlled. In a cooling system, the exact flow and pressure at any point in a system depends on each component and the amount of restriction that they provide to water flow. Different parts of your engine offer different flow characteristics. For example, the water jackets in an engine block are large in comparison to those in a cylinder head, so water flows through the block with much less restriction and therefore much less pressure. As pressure rises due to restriction, water pumps have a harder time keeping the volume, or flow, of water sufficient enough to cool the cylinder heads in extreme combinations, which can be a serious concern on boosted applications in particular. Remember, horsepower is heat. It’s super easy to cool a 150 horsepower Honda, which is why they have tiny radiators. Try to cool with that radiator and the same amount of water pump flow, and you’ll have big big problems.

Mechanical vs Electric…

Since the first hot rodder put an electric drive setup on a water pump, the debate over mechanical vs electric has been on like Donkey Kong. And the truth is both have their place. I remember very well the first electric water pump setup my dad had on his Camaro. It was one of Moroso’s units that featured a small electric motor on a bracket with a dedicated set of pulleys to drive the stock mechanical water pump. This setup is fine for some drag race only cars, but that sucker was never meant to cool and engine driving down the freeway. But, that doesn’t mean a true electric pump isn’t good for street and race applications. They can be great for a variety of vehicles, but there are limitations that in some cases require the benefits that a mechanical water pump can provide. The obvious downside to a mechanical water pump is the fact that the engine needs to power it, and that means that a significant amount of horsepower can be lost spinning one sufficiently to cool your hot rod, “and that’s a real shame to give up precious horsepower considering how hard we work to make it!” says Don Meziere. “So for most performance applications where actual wide open throttle time is limited our electric pumps have been used successfully. We have customers come by and share stories of their vehicles producing in excess of 800 horsepower, used for road racing, and the electric pump keeps up just fine. Of course there have been tech calls where we are wondering why in the world the customer’s system is not working well and we need to get a closer look at each component to get to the root cause. Typically we will recommend mechanical pumps be used for any towing application, any application where turbo boost exceeds 35 PSI, any N/A or boosted engines used for continuous wide open throttle and in excess of 600 HP. These are the places where block pressure and more specifically pressure in the cylinder heads becomes important to avoid detonation.”

One key thing here that Don mentions, is “applications where wide open throttle is limited.” No matter how much you brag to your buddies, the truth is that most people, even us crazy hot rodders and racers, are at wide open throttle for a fraction of the time we are actually driving our cars. When is say fraction, I’m talking single digit percentages, even for most pro touring guys.

And speaking of Pro Touring guys, check out Meziere’s LS water pumps that allow the full front accessory drive to operate properly by encompassing a free spinning pulley on their electric waterpump.

Remote vs On-Engine: Which one is better?

On the S10, we have a remote mounted Meziere pump that mounts directly to our Ron Davis Radiator, Fan, And Shroud assembly. There is a billet aluminum mounting flange that is built into the radiator that the pump mounts to. For us, there was one major reason to run this particular pump, and that was the fact that we wanted our cooling system to be removable for running on the dragstrip. Because we run on Alcohol on the track, heat is not an issue in our short runs, but saving 40 plus pounds is. Hence the remote mount water pump. Meziere reinforces this, saying that packaging is the most common driver for the decision between remote and engine mounted water pumps. Don also said that “For a typical V8 application, removing the pump from the stock location can be the difference between an engine fitting where you want it to or some significant vehicle modification (get the torches and welders out, boys!).”  Moving to a remote pump often opens up the access to more easily adjust the camshaft timing as well.”

One other interesting note, especially since we know guys who have run Meziere electric water pumps on their cars for a jillion miles, is the fact that Meziere has found that the remote pumps tend to live longer. They believe the reason is that the electric motor windings, brushes, and seel are not subjected to engine harmonics. This tends to make sense considering some of the things we are learning from the guys at Innovators West about harmonic balancers, but that’s another story.

The short answer is that you should choose the water pump that best fits your available space and application. Keep in mind that an engine mounted electric pump bolts right on and you can attach regular radiator hoses to it (OR AN, Meziere will set it up however you like.), which means simple installation. The remote pump will require lines and fittings, which can add some expense, but may be a cheap alternative to stuffing that big block in your SMART car with an on-engine pump.

How does cooling system pressure affect the efficiency of the water pump?

Remember how we touched on pressure when talking about the mechanical vs electric pumps? Well, there are actually two kinds of pressure in your cooling system. One is the pressure that is created by the heat of your engine expanding the coolant within your cooling system. This is the pressure that is being controlled by your radiator cap. Meziere refers to this as the static pressure. They refer to the second type of pressure as dynamic, and this is the pressure created by the pump itself. In truth it is the difference in pressure from the outlet side of the water pump and the inlet side of the water pump, and will be highest as it exits the impeller cavity of your water pump, whether mechanical or electric. The water in your cooling system will see different pressure drops as it travels through different areas of the block and heads, and again as it moves through the radiator. Ultimately, the lowest pressure that your system will see is at the outlet of the radiator where fluid returns to the water pump.

“The largest benefit of pressurizing the coolant is the increase in boiling temperature. We all know that boiling fluid will not cool an engine. For each pound of pressure inside of the system the boiling temperature is raised by roughly 2.5 degrees F. Considering pure water with a boiling temp of 212 inside of a system with a 16 pound cap you will have the opportunity to go to (212+[16*2.5]) 252 before the fluid will boil. Dynamic pressure added by the pump increases the pressure where it matters the most – inside the cylinder heads. Fluid needs to flow well over the backside of the combustion chambers or you are in for some big trouble. If your coolant reaches boiling inside the cylinder head you will see detonation very soon thereafter.” says Meziere.

Have you ever seen an engine that won’t cool, even though it has no thermostat in it at all? Have you seen someone use a restrictor in place of a thermostat? While not EVERY system requires a restrictor or thermostat to keep the engine cool, although with rare exception you should be running a thermostat for your engine’s well being, the thermostat and restrictor both provide enough restriction in the flow of coolant out of the engine to help maintain that dynamic pressure level that is required to keep coolant in contact with the walls of the coolant passages. ie Around the combusting chambers in your engine.

Is Gallons Per Minute, GPM, the end all spec that matters when choosing a water pump? How is it measured? Is there an industry standard?

Here’s what Don Meziere said when we asked these questions. As we suspected, there can be some trickery when looking at specs on water pumps, much like the fuel pump world. “Gallons Per Minute has been the standard for our industry and has been used as a “snapshot” of what the pump is capable of. The truth is that it’s a really problematic number, with many ways for any manufacturer to manipulate it. It is supposed to be a “free flow” number with zero back pressure and zero inlet pressure. Although we can get close it is very hard to get all of the details right. Any amount of elevation on the fluid feeding the pump can be considered inlet pressure and therefore aids the pump in flowing – producing higher numbers. Any curve or bend in an outlet hose can be considered backpressure which could also contaminate test results. Larger or smaller hoses can change the way the pump performs. The best way to know about a specific pump is to look for the manufacturer’s pump curve. It will show how the pump performs through a range of back pressures. There will be a free flow end to the curve with zero back pressure and a zero flow end showing maximum pressure the pump can push before “dead heading”. The graph should also incorporate power draw (Amps for electric, HP for mechanical) which is very relevant.”

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I have to admit, I’ve used a lot of Meziere pumps over the years, and can only remember looking at the graph once. Like most guys, I order what they tell me will work and bolt it on. But being as I’ve been on a budget more times than not, I’ve done a lot of Summit shopping and look at pumps with varying specs, some good and some bad, that range in price dramatically. I suppose that as I’ve learned a few things over the years, one of them is that you don’t short change yourself on cooling. If we’re willing to spend thousands to make a few more horsepower, we should also be willing to spend a few bucks on cooling the beast down rather than blowing it up due to overheating or detonation.

How many Gallons Per Minute does someone need?

Don Meziere – “Just enough…not too much.