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Installing the right racing water pump or making some simple modifications can save as much as seven horsepower.

 Water pump damage occurs over time as heat and contaminants destroy the internal parts of the pump. Some of this damage is evident, but bearing wear or impeller deterioration may not be so visible. If the remanufacturer reuses these components, their performance can compromise the system, reduce its cooling capability and cause more damage to your engine. It is only a matter of time before the unit fails again.

 Silicone sealant on water pump gasket

Use silicone sealant very sparingly, if at all. Especially do not make gaskets with silicone. The sealant can get into the pump and cause severe damage. Many engine builders no longer use silicone sealant at all. Gaskets have come a long way and despite what the kid at the auto parts store tells you silicone is not necessary. With engines that require constant care, like in drag racing, many racers use Hylomar sealant. The stuff is non-drying and it allows parts to be removed and replaced without cleaning. Edelbrock water pumps utilize "O" rings instead of the paper gaskets.


An automotive water pump is a precision part designed to work in a highly stressful environment. In this post, we visit how a small variation in the gap between the impeller and the pump body can cause overheating, even pump and engine damage. Just as with an engine, a minor defect in a pump or its components can result in poor performance. A rebuilt water pump may pass a visual inspection, but hidden imperfections like bearing wear or impeller deterioration may not be so visible in reused components. This example can leave you thinking “Why is my motor still overheating when I just replaced the water pump?”. There are things that remanufacturers do that are not up to racing and high performance standards. They install oversized bearings to make up for the loss of clearance the hub may have suffered when they removed the bearing from the old pump. The press fit is a hit and miss, and it is often out of OE specs, and this can cause a catastrophic failure. The mounting holes may become enlarged which can weaken the housing, cause cracks and leaks. Remanufacturers sandblast the housings. This procedure leaves pits and scratches in the housing and the mounting surfaces. The best way to avoid problems when replacing a water pump for racing, towing, street performance or a street rod is to purchase a new pump from a manufacturer that specializes in racing parts.

Precise machining practices are essential in maintaining the hubs and shafts perfectly perpendicular to the body to eliminate excessive bearing load, noise and to reduce power losses and heat.



The number of vanes (fins) does not necessarily increase the pressure and flow from a water pump. It is the impeller clearance to the pump body that maximizes flow and pressure. We measure the Impeller clearance from the top of the impeller vane to the bottom edge of the housing raceway. This clearance is critical in assuring maximum pressure and flow. The small clearance reduces the amount of water under pressure that seeps around the impellers. Leakage at that point causes eddy flows and cavitation. Both events cause overheating and damage to the pump. The manufacturers must use precision tooling to achieve the tightest clearance possible.

  This calculator from http://www.blocklayer.com/pulley-belteng.aspxis very helpful in calculating pulley ratios and belt lengths. Remember to avoid slowing the water pump speed excessively to prevent loss of pressure and possible overheating.


Here’s a standard technique in testing for a low-flow situation: 1. Drain the coolant level down to the radiator tubes

2. Get the engine hot

3. Shut the engine off for ten minutes and let it set to make sure the thermostat is wide open

4. Start the engine and run it at 3000 rpm.

5. Look down into the top of the radiator tank with a flashlight, and you should see active circulation, if not, then you are dealing with a low-flow situation.



Heavy duty water pumps include thicker rib supports for the bearing. Those can still break if overtaxed. Always inspect the fan and blades for signs of wear. Cracks can form over time and weaken the fan blades' integrity. Bent blades can cause out of balance concerns that can shorten a pump's life. Image courtesy of ASC Industries.


Most V8s built in the 60's and 70's came with a range of power between 185-375hp. With the availability of all the aftermarket performance components available it is easy to achieve horsepower figures much greater than stock.  Originally installed water pumps were not designed for this additional power and the increased demand on water flow. Using a stock pump, even a blueprinted one, on a built engine can cause spectacular failures. Again, stock parts belong on stock vehicles. Racing and high performance engines deserve purpose built parts.


Some advice from ASC Industries and Water Pump University

Fans, Clutches, and Spacers

The goal of any retrofit is to get the fan spaced into the shroud for max cooling, but be careful how you get there. Most manufacturers never offered a spacer and fan clutch combination. A fan spacer by itself or a fan clutch by itself is OK, but when used in combination the outcome can be catastrophic. When you choose a spacer, be sure it is a snug fit on the shaft, and never stack spacers. Always remember that the pump was designed using a factory fan and clutch, and any variation from that will cause an additional load on the pump's bearing. This can shorten the life of the pump's bearing and seal. Make sure that all components being used mate well with each other. Any misalignment or vibration in the components mounted in front of the pump will shorten the life of the pump's bearing and seal, and will in some cases cause catastrophic failure where the housing of the pump fails - causing extensive damage.  


In what direction, will my pulley system be turning?

If you replace the water pump, keep the rotation direction in mind. As a rule, engines from around 1985-1986 and up run in a reverse rotation (counterclockwise if you are looking at the engine from the front of the car). The reason for this in most cases was the introduction of the serpentine belt. A good rule of thumb if the pump is driven off the back side of a serpentine belt it will be reverse rotation. Automotive water pumps made before 1985-86 will rotate in a standard or clockwise direction (looking at the engine from the grill). Failure to determine the exact rotation will directly affect the performance of the engine's cooling system, and no one wants a hot running motor. For older V-belt systems one can buy a serpentine conversion kit but see to it that the pump is turning in the correct direction.

Sheet metal baffle on water pump impeller

Is your race motor still overheating even though you tried everything that could help solve the problem? If you still run a stock water pump, try installing a baffle like the one in this picture. The plate will prevent the coolant from escaping through the back of the impeller. What is more, keep the space between the water pump impeller and the pump body tight, in the .030-inch range. Install the appropriate thickness feeler gages under the impeller and tap on it lightly until it bottoms on the gages.

Reducing the clearance between the impeller and the pump prevents eddy flows, and it can improve coolant flow by as much as 15% while keeping the engine running cooler. What is more, a tight impeller creates some additional pressure in the heads, further reducing the water boiling point and the risk of detonation. While these “blueprinting” fixes can help if you are on a budget or if there is no racing water pump available for your engine you must remember that stock water pumps are not made for racing, and they are not recommended for a race or high performance vehicle.

With stock water pumps, cavitation can occur at increased engine speeds such as when a stock engine has been built to produce more RPM. Cavitation is the formation of vapor (steam) bubbles in the cooling system. These bubbles form when the coolant temperature reaches the boiling point determined by the pressure that is present in the cooling system. http://www.waterpumpu.com/news-blog-water-pump-cavitation-and-solutions.aspx


 We can improve water pumps with sheet metal impellers by adding a plate on the impeller to form a secure pocket for the water to accumulate. The impeller can be driven down to a clearance of about 30 thousands of an inch with a small hammer and a socket. Race and performance water pumps like those from Edelbrock run tighter clearances than .025-“, but their tolerances are super accurate, and we should not attempt those on auto parts pumps. Insert a feeler gage between the impeller and the pump body to set the clearance if you wish to "blueprint" your stock water pump.


When any of the components of a cooling system is badly corroded, it will cause overheating, leaks and possible additional engine damage. For towing, street performance and off-roading use the correct amount of antifreeze, or Evans coolant to ensure maximum durability and performance. In racing use distilled water and a good all-purpose water wetter like Redline’s “Water Wetter.”

Rusted water pump in racing engine

The rust from this pump has probably propagated throughout the cooling system; this condition warrant flushing out the whole system. If you use a quality radiator, or, an original one made of copper, a qualified shop (preferably one equipped with sonic cleaning equipment) should be sought to flush out the radiator. The block and the heads will also need a strong flushing.

If your cooling system is badly polluted and you run a quality radiator, or, an original one made of copper, a qualified shop (preferably one equipped with sonic cleaning equipment) should be sought to flush out the radiator. When any of the components of a cooling system is damaged this badly, it will cause overheating, leaks and possible additional engine damage. For towing, street performance and off-roading use the correct amount of antifreeze, or Evans coolant to ensure maximum durability and performance. In racing use distilled water and a good all-purpose water wetter like Redline’s “Water Wetter.”

Measuring the water pump hub height

The hub height will determine the location of the pulley and the belt. Compare the measurement with the manufacturer’s specifications before ordering.  Image courtesy of ASC Industries.

Edelbrock racing performance impeller

Edelbrock's racing water pump impellers are cast of sintered metal and machined to extremely tight tolerances. The design avoids cavitation and loss of power by preventing the water from seeping between the impeller and the pump body. What is more, the impellers were designed with the assistance of computer aided drafting to maximize the flow and minimize power needed to turn the pump. The pumps can now turn more slowly and maintain the all important coolant pressure.


We can measure the hub height from the base of the gasket surface to the top of the hub where the pulley will bolt. When choosing a pump, it is important to assure that all the pulleys line up. Another thing to keep in mind is the bolt circle on the hub on which the pulley and fan will bolt. There are several different sizes, both metric and standard, and this applies to the threads as well.  

Gilmer belt pulleys

 If you use a Gilmer belt arrangement, plan to run the hub near the center of the pulley.









Content from ASC Industries: http://asc-ind.com/wp-content/uploads/2016/11/AIRTEXGalvanicEffect.pdf

An important concept regarding the endurance and performance of the water pump is electrolytic metal erosion or EME. This is also referred to as the galvanic effect. With the ever-increasing use of dissimilar metals in engine components, plus the higher reliance on electronics, the problem of EME is brought to the forefront. This electrical activity is not a voltage leak from the electronics in the vehicle. If you disconnect the battery, the same voltage is present. The problem is from the cooling system acting as a storage battery. The system cannot store electrical energy while cooling the system - and it cannot transfer the energy to operating the electrical system. Therefore, erosion of components occurs. To measure the EME activity in any cooling system, simply use a multimeter. Open the cooling system at the radiator cap, stick the positive probe of the meter into the cooling system and ground the negative probe to the engine block. With the meter set at the lowest setting for voltage, you will find electrical activity in just about every vehicle tested. Be aware of the common EME or galvanic effect within an engine. It is commonly mistaken for corrosion caused by oxidation in the cooling system or erosion from the fluid that flows through and around the insides of the engine. Also, it is sometimes simply assumed to be caused by a defective casting. To minimize the galvanic effect in an engine, make it common practice to regularly change the coolant. When installing a new water pump, always clean the cooling system with a chemical cleaner and reverse-flush all sediment, rust, and scale before removing the old pump.



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