Prevent a cooling system crisis by paying attention to signs

Without question, today’s vehicle technologies far surpass those of a few decades ago. As good as technology is, it has a downside — neglect. It’s estimated that unperformed maintenance amounts to a staggering $60 billion a year. Cooling system maintenance, or lack thereof, represents a sizable portion of that number.

Let’s investigate some of the routines that you can perform to both keep your customers on the road and help your shop’s bottom line.


Start with a complete visual inspection of all belts and hoses, hose connections and the radiator. Remember that although a hose may look okay from the outside, hoses actually begin to weaken from the inside out. This is triggered by electrochemical degradation, which creates minute cracks in the wall of the hose. Eventually these small cracks extend from inside the hose to the outside. This provides a pathway for coolant seepage and weakens the hose. Coolant hoses should be replaced at least every four years, or more often if required.

Next, pressure-test the cooling system with a pressure tester, testing the system to the pressure rating of the cap. Make sure you use the right adapter to ensure a good fit at the radiator or pressurized reservoir. Then, with the system under pressure, inspect potential leak spots, looking for signs of coolant. Periodically check the pressure reading on the tester to see if the pressure drops off. A drop means that the system is leaking somewhere, so be exact in your inspection. Don’t forget the heater core and its connections, along with common leak locations on the engine itself such as the intake manifold, water pump and freeze plugs.

Don’t forget to pressure-test the cap. A faulty pressure cap can contribute to cooling system problems, impacting the life of coolant and the overall cooling system. A pressure cap does more than keep coolant in; it raises the boiling point so the system operates as designed. In fact, faulty pressure caps have been linked to some of the problems that had been previously blamed on long-life coolants.


Coolant replacements often go overlooked because of the misperception that if the coolant meets freeze protection or anti-boil requirements when checked with a hydrometer, then it must be okay. This is certainly not the case, as the additives that protect the cooling system break down with age. For a more accurate assessment of coolant condition, use test strips that evaluate the coolant beyond freeze protection.

Generally, standard ethylene-glycol antifreezes should be changed every two years or 24,000 miles. Some cars use long-life coolants that claim to last five years or up to 150,000 miles. There is much controversy in the industry as to the long-term validity of these claims, but be aware that standard ethylene-glycol and long-life coolants shouldn’t be mixed unless absolutely necessary. Mixing them detracts from the qualities they each possess. Always check the manufacturer’s recommendations for coolant, as there are specific coolant requirements such as silicate-free for Japanese cars and phosphate-free for European cars.

When filling the system, make sure you bleed the cooling system to purge all air. Air pockets can cause unstable temperatures and damage to the engine and cooling system.


Proper thermostat operation is critical to the cooling system and it’s a good idea to check this during your inspection. With the engine warmed up, you can read this right through your scan tool or by using a contact thermometer/pyrometer at the thermostat housing. A thermostat that allows the engine to run too cold can prevent closed-loop operation, poor fuel economy and other woes. If you’re replacing coolant anyway, recommend a thermostat replacement to your customer as cheap insurance.


Studies show that the chances of a serpentine drive belt failure rises dramatically after four years or 50,000 miles. Random cracks across the ribs are a sign of normal belt wear; they don’t mean the belt needs to be replaced immediately. Eventually, the belt will show multiple cracking with cracks spaced every 1/2” to 3/4” apart. If ignored, chunks between the cracks will break off. Always replace the belt when you find multiple cracks or missing chunks. Even if the belt only has random cracks, recommend a new belt to your customer. You may need a special serpentine belt tool, depending on the vehicle you’re working on.

Don’t forget to inspect the idler and tensioner at the same time. Check for rough bearings and damage or looseness at the tensioner.


Check the operation of the electric cooling fan as part of your cooling system regimen. On most cars, the fan should run when the coolant temperature reaches the threshold of the fan switch. The fan should also come on with the A/C when the vehicle is stopped or traveling at slow speeds. At higher speeds, usually above 25 mph, the powertrain control module turns the fan off because there’s adequate airflow through the radiator.

If the fan doesn’t work correctly, make sure the engine reaches normal operating temperature and that all electrical connections are secure throughout the fan circuit. Don’t forget the ground connections while you’re at it. Replace any bad parts.

Although electric cooling fans are the norm today, there are still a good number of rear-wheel-drive vehicles, like pick-ups and SUVs, on the road with mechanical fans. Many of these vehicles use a thermostatic clutch to control airflow efficiently while reducing engine load.

Fan clutch failures often go overlooked. An inoperative clutch can cause engine overheating and excessive high-side air conditioning pressures when the vehicle is idling or moving slow in traffic. A locked clutch hurts fuel economy and performance because of the high load on the engine.

With the engine off, inspect the clutch hub for signs of fluid leakage and grab the fan to see if you can turn it. If there’s fluid at the hub or the fan won’t turn, replace the clutch.

Checking fan clutch operation is easy. With the engine cool, cover the radiator to limit air movement through its fins. Start the engine, turn on the A/C and let the engine idle. The fan should turn slowly compared to the engine’s speed and churn little air.

After the engine runs for several minutes, you should hear the fan begin to roar as the clutch engages. Then, uncover the radiator and wait to see if the clutch disengages after the fan cools the radiator for several minutes. If the clutch doesn’t disengage after the engine cools or if the clutch doesn’t engage as engine temperature continues to climb, replace the clutch.

Proper cooling system service keeps your customers rolling, while building business for the shop. With customers keeping their cars longer than ever, opportunities abound.