Quick Tip Saves Time When Replacing Coolant Pumps

When performing an engine overhaul, it’s very tempting to install new parts without taking the time to carefully inspect them first. But omitting that step can cost you time, your customer downtime, and lead to lost productivity.

What follows could be a typical scenario in which the impeller direction on a coolant pump plays a critical role — if only the technician had taken a close look before installing the pump.

Old or damaged coolant pumps can contribute to the need to make major repairs to an engine. But technicians also routinely replace this part as a precautionary measure, since it is next to impossible to tell how much life exists in a pump. Whatever the case, let’s say there is a fresh coolant pump waiting with the other parts for the overhaul.

Taking the pump out of the box, you see that the casting and all the bolt holes look correct. The height of the input shaft and drive type seem right. You bolt it on. After finishing up the engine reassembly and installation, you fill the cooling system (if the engine was out of the chassis). Everything looks great and you fire up this fresh engine. It starts right up and sounds great! Congratulations, another job well done.

Water PumpAnd then weird things start to happen.

First, there seems to be a little trouble topping off the cooling system. Coolant keeps burping out of the top of the radiator or fill tank. Then, the temperature seems a little too high sitting at idle. Maybe the new thermostat installed during the overhaul is sticking? Yet, the coolant in the radiator is hot and the top radiator hose is hot as well. Revving the engine pushes coolant out the radiator or tank. Still, the engine is not overheating. Something’s not right.

After the engine cools enough to remove the radiator cap, you move forward to see what may be going on. Starting the engine, it looks as though there is no coolant flowing through the thermostat and top hose. Taking the thermostat off and testing it shows it to be okay. The diagnostic information for the cooling system indicates the coolant pump could be faulty. But it’s NEW! So, you decide to test the coolant flow without the thermostat and discover there is a very limited amount of coolant flowing out of the top hose to the radiator.

Taking the coolant pump back off the engine, you see it looks perfectly fine. However, when comparing the new pump to the old pump with more care, you notice something odd. The impellers are pointing in the opposite direction.

As it turns out, there are some applications that work in the opposite direction as the result of belt type or routing. So, it is important to take a look at the impeller direction before installing the pump. Having made this mistake once myself, I know it is easy to overlook when the rest of the pump looks exactly the same. On some applications, it is even difficult, if not impossible, to see the impeller direction. Using a truck repair information resource like TruckSeries from Mitchell 1 can help.

But simply taking that little bit of time to thoroughly inspect and compare new parts can save a ton of time and frustration. The little details that seem so simple are more often than not the things that end up causing all sorts of trouble.

About the Author

Jake Schell

Jake Schell is an editorial consultant with Mitchell 1. Previously, he served as Product Manager for the Commercial Vehicle Group from 2002 to 2023. Prior to joining Mitchell 1, Jake spent 20 years as a technician. He holds a Chevrolet Master certification in the transmission category as well as ASE certifications in both cars and trucks.