Cooling System Basics: Checking Belts, Pulleys, Tensioners and Pumps

Oct. 31, 2019
When a vehicle rolls into your service bay for an inspection or any other problem, it’s a good idea to make sure that the vehicle gets a good visual check as well. You want to take care of your customers and give them a good sense of peace of mind so they know you are looking out for their best interests.

When a vehicle rolls into your service bay for an inspection or any other problem, it’s a good idea to make sure that the vehicle gets a good visual check as well. You want to take care of your customers and give them a good sense of peace of mind so they know you are looking out for their best interests.

That’s how you generate a repeat customer. There are many systems on a vehicle that should be inspected besides safety critical areas like brakes, tires, etc. The engine has to be operating correctly, fluid levels must be maintained properly, and all other components need to be working as designed.

One of the more important systems is the cooling system. If the cooling system isn’t keeping the engine cool then an overheating scenario will occur and that could get your customer overheated as well.

Cooling systems have become more and more complex as modern technology seems to creep in with today’s new vehicle technologies. It used to be years ago that you had one type of antifreeze, a water pump, one or maybe two belts, one thermostat, heater core and a radiator. Gone are the simpler times. Hello to multiple cooling systems, an increase of components and the addition of electronics. 

Today’s modern cooling systems potentially feature multiple thermostats and may include electronic thermostats to boot! Would you ever consider an exhaust manifold being a coolant system part?

A 2013 Ford Focus ST Eco Boost engine has an integrated exhaust manifold incorporated into the cylinder head (see Figure 1). This is an example of why it’s more important to stay on top of technology.

Today’s vehicles are more efficient in keeping the engine at the correct temperature than the ones that we’ve seen in the past, but they still need to be maintained and the maintenance needed for these systems is just as critical as before.

As everyone knows, the heart of a cooling system is the coolant that is used to maintain engine temperature. The type of antifreeze used is just as important as the condition of the antifreeze. Antifreeze doesn’t last forever and it breaks down just like engine oil does.

This article isn’t going to get into the specifics of which antifreeze to use or how to test it. We can save that for a future article. The point I’m trying to make is following the factory recommended guidelines and specifications that your customer’s particular vehicle calls for is the best rule of practice.


When performing a cooling system inspection, the first thing that has to be done is a close visual inspection. Look for any sign of a leak whether it’s an external leak or an internal one.

For external leaks, inspect the hoses for splits around where the hose clamps are, any rubbing or chafing against another component or obstacle (see Figure 2). Pay close attention to the way a coolant hose is routed. It’s possible that a hose was installed incorrectly or maybe it was an incorrect hose replacement to begin with.

With the engine cold, give the hose a couple of squeezes and notice if the hose seems very soft or squishy to the feel. It’s possible the barrier wall inside the hose has deteriorated due to an unknown substance like oil or another chemical that has broken down the barrier. That could be a rupture waiting to happen, especially under a high pressure high heat condition.

Other external leak points can be at the water pump weep hole, heater core inlet and outlet hoses as well as the core itself. Other potential leak areas include intake manifold gaskets, cylinder head gaskets, thermostat gaskets and cylinder head or block freeze plug areas. The radiator can develop leaks at the core and especially at the seams of the tank.

Newer vehicles, as you know, have plastic tanks that are attached to an aluminum core. That particular area is prone to start leaking. The methods you use to check for leaks are the same today as you performed in the past. Systems under pressure always tend to show a leak a lot faster than one that’s not under pressure. That’s not to say a system can leak without pressure as in some conditions a leak will show up under an ambient temperature state.

Belts and pulleys

So what makes a coolant system operate besides having the correct coolant and the right amount of it? It’s the mechanical moving parts that place the system in motion. Those parts consist of a water pump, serpentine belt tensioner, an idler pulley or two, a power steering pump, an air conditioning compressor, and the alternator (see Figure 3).

All of those things are tied together with a serpentine belt or a combination of serpentine and/or V belts. When checking the mechanical aspect of the cooling system, every component has to be operating correctly. The part that is the most crucial is the belt.

Depending on the vehicle, a combination of multiple belts could be used. If they break then everything stops. The belt is also the component that is the weakest. If a component starts to fail, the belt will tend to slip on the pulley thus creating an excessive amount of heat.

Over time the belt will become worn or glazed and it will stop gripping the pulley. You can tell that a belt is glazed by not only looking at the belt for a shiny appearance, but it feels a little more brittle and not quite as flexible as it should be.

Look for any cracks that tend to develop on the wearable part of the belt as those could be potential failure points. Belts also tend to fail due to different chemicals like oil and coolant leaking on them as well as a sharp object rubbing on them.

Make sure that there are no external leaks found before a new belt is installed. If you don’t, the new belt life span will be decreased significantly.

Belts should have the proper alignment checked before installing a new one. Using a belt alignment tool can aid in proper alignment (see Figure 4). The alignment can be off due to a few factors such as an accessory not properly installed or an incorrect pulley being used on that accessory along with a pulley spacer being used or not being used.

Remember to visually look at the new component that you are replacing and make sure it’s exactly like the one you removed.

Have you ever heard a chirping or squeaking noise while the engine is running? Chances are that noise is coming from the belt gliding over the pulleys. Some of the pulleys on the vehicle may feature a series of grooves. What could be happening is there is a buildup of dirt or debris getting inside those grooves and when the belt is turning, the ridges from the belt aligning in those grooves will create a noise that can be annoying to the customer.

When you are replacing a belt, before you install the new belt, look over all the pulleys and remove any debris you see in the grooves of the pulley. This goes for smooth pulleys as well.

Use a small wire brush and spin the pulley while cleaning the area of the pulley. While wearing safety glasses, use a small amount of compressed air to blow away excessive debris from the pulley. We know that the pulleys need to be clean and in good shape so our belt will grip them correctly, but what about pulley condition? Pulleys need to be free from damage both visually and mechanically. When performing a check on a pulley, make sure that there aren’t any extra grooves worn into the pulley, nicks or burrs that have developed on the pulley, especially when dealing with plastic pulleys.

Check that the pulley isn’t excessively worn, as the belt will wear a pulley down over time even though there isn’t any damage to the belt system. The pulley must feature the correct diameter for the application. If any of these inspections reveal an issue, replace the pulley.

Also check the pulley for excessive side-to-side play. The pulley rides on a bearing or features an integrated bearing. Spin the pulley with the belt removed and listen for noise that may indicate wear or grit. When you spin the pulley you will also be able to feel the drag of the bearing it rides on. Excessive drag, noise, along with too much play is cause for a pulley replacement.

Pulleys that fail can damage the component they ride on along with the belt. Sometimes a nearby component can be damaged. For example, if a broken pulley or belt gets ejected into the radiator and punctures the core. You just went from a $50 pulley repair to a $200-plus radiator repair.

These pulley checks should be performed on every component that the belt rides on. Make sure that all accessories are operated for normal belt operation. Air compressors need to be turned on, power steering pumps should be operated from steering stop to steering stop and alternator efficiency can be checked by loading the electrical system and making the alternator work.

Water pump

Another component that needs to be checked closely is the water pump. The water pump’s job is to circulate coolant in and around the engine. Obviously a malfunctioning water pump can create a lot of havoc. Water pump designs can vary among today’s vehicles. There are pumps that are belt driven and some are electrically driven. Some belts are driven by the engine’s timing belt.

When you are performing a cooling system check you typically don’t check a timing belt-driven water pump due to its difficult access. But if you are doing a timing belt service, a water pump replacement in my opinion is a necessary step and part of the job. I don’t have to tell you what can happen to a timing belt if a water pump fails that’s being driven by a timing belt.

As with a conventional cooling system check, you check the timing belt components just like you would any other belt driven component. When checking an engine’s water pump that’s belt driven, look for the water pump’s weep hole for signs of excessive leaking (see Figure 5).

Check the mounting of the water pump for leaking gaskets, missing mounting bolts and or loose bolts. Inspect the pulley like you did with the previous pulley inspection.

If the customer is stating that the engine is running hot, then check the water pump flow at the radiator fill neck or tap into a coolant hose and check for proper flow. A water pump impeller could be broken off completely inside the pump or the impeller could be missing pieces (see Figure 6).

If flow is suspected of being a problem then removing the water pump from the vehicle for a visual inspection will be needed.

Checking the belts, the different pulley components and the rest of the components that make up the parts of a properly functioning cooling system is essential to keeping the engine running at the proper temperature and efficiency. A cooling system that’s not working properly will also have a profound impact on the air conditioning system.

If the engine isn’t running cool (temperature too high) the air conditioning system will run poorly. If the belt is slipping on the air compressor pulley and not spinning the compressor’s pumping ability fast enough, the A/C system won’t be able to do its job properly. That’s just one reason a careful inspection of the components involved in the cooling system is extremely important.

As I mentioned earlier, modern cooling systems still use a lot of the same components as the older style systems. The difference is that there are more components involved and they are more efficient in keeping the engine running at the correct temperature. The late model systems like those found on a Ford Focus, as an example, (see Figure 7) have a grilled shutter system that controls the air flow during different types of operations (see Figure 8). From cold start up to operating temperature the grill incorporates a shutter vane type system that monitors and controls air flow through the grill. This is just one aspect that may be found in a late model cooling system.

When a vehicle rolls into your service bay, make sure you do your due diligence and give that vehicle a good inspection. Checking and preventing premature failures before they happen will not only keep the engine cool and working properly, but you will keep the customer cool as well. 

Preventing the customer from overheating is what makes a repeat customer for life.   ■

Edwin Hazzard owns South East Mobile Tech in Charleston, S.C., which is a mobile diagnostic and programming service providing technical service to many automotive and body repair shops. He has 36 years’ experience in the automotive industry. He currently is an automotive trainer, a board member of TST (Technician Service Training), a member of the MDG (Mobile Diagnostic Group), a member of the Professional Tool and Equipment advisory board for Pten magazine, a committee member of Nastaf, and is a beta tester for multiple tool makers.

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