Errors and Failures in Cooling Systems

Thee cooling system in an automobile is very crucial. The heat generated not only reduces the efficiency of the vehicle but also poses a serious threat to the components itself. The heat which is trapped in the powertrain system can cause irreparable damage to the system. Even though we take utmost care and sufficient factors of safety are considered, there are several errors that can arise throughout the functioning of the system. We will look at a brief of all such errors and failures that can arise during the working of our cooling system.

  • Radiator Damages –
  • Fin Damage –

The fastest way to get a damaged radiator is to hit something. Small rocks can do a number on your aluminium radiator if it hits just right. Bent fins are not a big deal, as long as they are smaller than a tennis ball. An area larger than that can cause some issues. If you find any bent or damaged fins, look at the tubes around them. The fins only dissipate the heat; it is the tubes that hold the coolant. Damaged tubes could have micro-cracks that will eventually turn into full-blown leaks.

Small fin damage is not a big deal, it happens. This is major fin damage. You need to repair the fine, as it is cutting off a fair amount of airflow. A pick works to lift the bent fins. Aluminium radiators often have perforated fins, so you can actually peel the edges off, revealing unbent fins. Just pull off the fin, and it breaks away.

Another common problem, especially among home mechanics (yours truly included) is the issue of bent fins. Radiator design hasn’t changed much in the past 100 years, save for switching the tanks from a top-to-bottom setup to a crossflow (side-to-side) setup. In all radiators, hot water from the engine flows into the radiator and then passes through a number of narrow tubes with fins on either side. Air flows over these fins (either from forwarding motion or pulled through by the fan) which dramatically increases the ability of a radiator to shed heat, allowing the water inside to drop as much as 30 degrees before going back into the engine block.

As important as these fins are, they are also extremely delicate, and sometimes we home mechanics have the bad habit of banging and shoving parts like the radiator into place. This can bend and damage the fins, which is never a good thing. “Any time you bend that fin, it will prevent the air from going through the radiator,” says Jason. “This will in turn affect how it can cool. Small rocks can bend fins, or if you hit a bird or debris on the road. If you’re into driving off-road, mud or dirt can get into those fins too, blocking the air the same as a bent fin would.” Jason recommends giving your radiator the occasional blast of water to blow out debris that collects over time.

If you have bent fins though, don’t get too worried just yet; a few bent fins here or there isn’t the end of the world or even your radiator. “If you have some decent-sized areas, like baseball-sized or larger, that could greatly affect the way the radiator cools,” says Jason. Even if you have a large area of bent fins, chances are your radiator can still be saved so long as the cooling tubes themselves aren’t pinched. “Most auto parts stores sell or loan what they call a radiator comb, which is used to straighten the fins back out. Unless the fins are broken, you should be able to straighten them out

1. Corrosion – If the outside of your car rusts, you’re sure to notice. But just because you don’t see it, doesn’t mean it’s not happening in your car. When you combine air, metal and liquid, oxidation and rust are bound to occur. All those ingredients are present in your radiator, which means rust is a real threat. If your radiator gets too rusted, it can end up with holes and leak or otherwise malfunction.

If your car is running too hot, check your radiator for rust. It should be easy to see on the outside, but you can also tell if the colour of your coolant becomes brownish. If you operate your car in cold weather climates, you should be especially vigilant for rust.

 this is the most common cause of sludge build-up in a radiator. Radiators, like most parts in your engine, are made of metal. Over time, antifreeze can degrade. As it degrades, coolant loses its protective qualities, PH levels change, and corrosion sets in. Once the corrosion begins, rust, sludge and scale build-up through the entire cooling system, including into the engine. This sludge can block the flow of coolant through the lines which cause the engine to overheat and leak. If left untreated, overheating and leaking can lead to very expensive repairs.

Dex-Cool – Some vehicles require a coolant called Dex-Cool. This coolant was designed to last longer than normal antifreeze, only needing to be changed every five years instead of two. Unfortunately, this new technology hasn’t worked entirely to the desired design purpose. According to complaints received by Consumer Affairs, Dex-Cool reacts with the plastic sealing surfaces, causing the intake manifold to leak. The residue left behind by the breakdown is very sticky and thick like mud. Only a chemical flush will remove the sludge. We suggest if you see this sludge build-up in your vehicle to take it to a professional for a chemical flush.

2. Clogged tubes – Another common radiator problem is a buildup of mineral deposits, which is often more commonly referred to as gunk. You know gunk when you see it — it’s a thick, unsightly, goopy substance that seems to exist solely to clog things up. Mineral deposits, by-products, debris and another obstructive buildup in your radiator make it harder for the radiator to flow the proper amount of coolant to the engine. If your car is overheating or getting hot too quickly and you don’t see a rust problem, leaks or detaching of the hoses, check inside the radiator for gunk buildup.

Once again, a good coolant flush is an answer.

Just as flushing the coolant can get rid of rust, it can clear all that gunk out of your system as well. Hy-per Cool Radiator Cleaner & Super Flush cleans the entire coolant system, removes coolant gel and deposits, and helps prevent the formulation of scales & Deposits. Be sure to flush, rather than just drain and replace the coolant, because draining will not get all the gunk out of the system, and you will have to deal with the problem all over again as it contaminates your new coolant.

3. Scale Formation – A diesel engine generates enough heat to warm a seven-room house during the winter. It must shed some of this heat to operate efficiently and prevent severe engine component damage. Two-thirds of this heat is lost through the exhaust and through the engine work. The remaining third must be pulled from an engine by the cooling system.

It is critical that all cooling system heat exchange surfaces remain clean. Hard water scale can block a cooling system’s ability to transfer heat resulting in overheating. Only 1/16 in. of scale will reduce cooling system heat transfer efficiency by 40%!

Calcium and Magnesium

Most cooling system water contains calcium and/or magnesium from drinking water supplies. Water that contains over 100 ppm of these minerals is considered “hard water”. It is wonderful to drink, but these minerals can form scale in engine cooling systems. As the concentration of these minerals increases, so does the probability that you will have cooling system scale problems. The level of dissolved solids in coolant water is generally referred to as the “total hardness” reported in parts per million (ppm). Cooling system additives that contain anti-scale chemicals can allow the use of moderately hard water. It is best to use water that is at least as good as the recommended water quality listed in the ASTM standards.

How Scale Forms

The potential for scale formation on hot metal cooling system surfaces is affected by a number of dynamic conditions. Some of the mechanisms and parameters that affect the formation of these deposits:

Water hardness – the harder the water being used in an engine coolant, the greater the amount of scale formation.

Temperature – as coolant temperatures increase, hardness salts (calcium and magnesium) in solution become less soluble and increase their propensity to plate out on hot metal cooling system surfaces
Flow characteristics – scale generally forms on the hot side of a cooling system and in areas of low or turbulent flow.
Entrapped air – any air bubble formation in a coolant area (bubbling around a hot source) increases the tendency for scale to form in that area.
pH – increases in pH will increase the potential for scale deposits. Damage to water pump seals.

Calcium and magnesium have the tendency to combine with the phosphates found in old-fashioned antifreeze and some additive packages. They form calcium and magnesium phosphate scale on heat transfer surfaces, especially on water pump seal faces. These deposits can destroy the flatness of a seal face, preventing the water pump seal from sealing. The result can be the destruction of the water pump bearings.

Cooling system problems that result from overheating caused by scale:

  • Cracked heads and warped engine blocks.
  • Oil temperature running abnormally high.
  • Failure of the cooling system fan to turn on.
  • Scale deposits on cooling system block heaters

Controlling scale deposits in an engine cooling system.

Scale removal: Before treatment is selected, a cooling system should be cleaned of all existing contaminants and hard water scale deposits.
Off-line cleaners: For cooling systems that contain a lot of oil and carbon, or systems that have not been cleaned for a long time, Penray recommends using Penray 2015 Twin Pac treatment. The Twin Pac product contains a very strong cleaner (Pencool 2010) that removes heavy scale deposits and rust. After the cleaner has been used, a conditioning rinse (Pencool 2011) is used to neutralize the cleaner and prepare the metal surfaces for new coolant.
In-service cleaner: Penray developed Penray 2001 treatment for on-line cooling system cleaning. This allows for cleaning of harmful mineral scale, rust and corrosion deposits from cooling system metal surfaces while the engine is in operation. 2001 cleaner is an inhibited cleaner. It contains a well-balanced corrosion inhibitor package that provides total metal corrosion protection while it cleans.

Clean your system when any of the following occurs:

  • When you notice water pump leaks (leaking around the weep hole)
  • When your cooling system fan isn’t turning on properly
  • When the cab or bunk heater isn’t getting any heat during winter months
  • When oil temperatures are running hot
  • When thermostats start sticking
  • Before changing the coolant

Preventing engine scale:

After cleaning your cooling system, select a corrosion inhibitor that contains a good scale inhibitor. Pencool 3000 cooling system treatment contains antiscale. Penray has thoroughly tested its scale inhibitor against numerous competitive cooling system inhibitors for anti-scale effectiveness.

Summary:

Scale build-up is serious and can destroy an engine. Intelligent preventative maintenance practices, including the proper use of Penray products such as Pencool and Penray cleaners, will prevent scale from forming. Pre-existing scale can be removed, restoring optimum engine cooling.

  1. Pin Hole Formation – Radiators are made of metal. Almost all metal ages and weakens due to oxidation. As the metal in your radiator weakens, it becomes susceptible to decay and failure. The constant heating up and cooling down of the radiator causes the same stress on the metal as bending a piece of wire back and forth in the same area on the wire. It will eventually break. In the care of your car radiator, the break is a crack along a tube that drains the coolant from the top to the bottom of the radiator. Under pressure, a great deal of coolant can be lost very quickly.

Everyone is familiar with rust that forms on unprotected iron. This is oxidation. Oxidation is corrosion that erodes the amount of metal available. As time passes, more and more of the metal oxidizes until small openings or pinholes start to appear. The high pressure inside the hot cooling system of the car will spray coolant through these tiny pores as you drive. Stop leak and other home remedies can slow the leaks for a while. The only real permanent fix is to replace the radiator.

  1. Leaks – Radiator leaks can be really hard to find. Unless the leak is large enough to leave puddles on the ground or under the hood, you may never know you have one until it is too late. However, there are some tell-tale signs on the radiator that can let you know that there is a small leak. Look over the fins on both sides. You are looking for oily or discoloured areas on the fins. Aluminium radiators are the easiest to do this as they are unpainted, but older copper and brass radiators discolour with leaks as well. On aluminium fins, the leak will look like a grease stain, depending on the size of the leak. Copper and brass radiators take longer to show leaks, but when they do, it is usually a mixture of green\orange oxidation and scale, exactly like a penny that has been in the water for a while.

The most common cause of radiator leaks is leaky hoses, but you can have leaks in the radiator itself, too, which can be a bigger problem. The coolant continually running from your radiator to your hot, running engine and back again creates a lot of pressure. That pressure buildup will eventually spell doom for your radiator hoses.

The hoses will either degrade or come loose, allowing coolant to escape the system, which will ultimately lead to overheating. If you see green fluid under your car or near it and you smell something sweet, it’s a sign your radiator is leaking. If your radiator is too corroded, this can cause a leak in the body of your radiator even if the hoses are intact.

  1. Incorrect Pressure cap or Incorrect placement –

The radiator cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of the water. The cap is actually a pressure release valve, and on cars, it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve opens, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring-loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

Most radiator pressure caps keep the system pressure at 16 PSI so the engine coolant can get considerably hotter without the fear that it will boil off. If there is no pressure in the cooling system, the coolant will boil off. On the other hand, if the pressure was allowed to increase above 16 PSI the cooling system, including the hoses and even the radiator, could simply burst or even explode if the conditions were right.

Never lose sight of the fact that a liquid expands as it gets hotter. As engine temperature increases, the coolant temperature increases as well, if the temperature exceeds the norm. The design of a typical radiator cap is such that liquid is allowed to escape; it does so by moving from the radiator to a reservoir.
When the car engine is shut down, it begins to cool the coolant contracts. If there were not a radiator pressure cap installed, the system would draw in air. The air causes poor engine cooling and is the main cause of cooling system component corrosion.

As the vacuum continues to build up, the two-way check valve, which is exactly what a radiator pressure cap is, goes to work. The cap allows the liquid that was transferred from the radiator to the external reservoir to be pulled back. As long as there is enough coolant, there is no room for air.

As a responsible car owner, you should be keeping your eyes on such things as oil level, transmission fluid level, windshield washer fluid level, and the level of the coolant in the reservoir. Most of these canisters are made from clear plastic making it simple to see the level. If the level gets down to about 50 per cent full, top it up with a fifty-fifty mix of anti-freeze and water.

Radiator pressure caps are an important component to the proper operation of your car; have the cap inspected periodically if it has failed to get it replaced immediately.

Hence if the radiator cap is chosen with a pressure lower than the desired value, it will open up too quickly and the system will overheat very soon.

If the radiator cap is chosen of a higher value than the design value, the coolant will be able to heat up to a higher value before the pressure cap opens up. This will cause the coolant to disintegrate and even cause damage to the system as well as the hoses and other components

  1. Incorrect coolant

Mixing different engine coolants or using the wrong coolant can impair the performance of the special additive packages; this can result in increased corrosion to the radiator. The protective layers in the cooling system gradually become thinner and more porous and the engine coolant needs to be changed at more frequent intervals. Using the wrong engine coolant can gradually lead to corrosion and damage to the water pump, radiator, radiator hoses and cylinder gasket. This can lead to damage to the engine in the worst case.

You always want to use the correct type of coolant in your vehicle. The wrong coolant or the wrong mixture of coolant and distilled water can cause your vehicle to overheat. If you’re worried about your coolant concentration and haven’t kept up on regularly-scheduled vehicle maintenance, a complete cooling system flush is in order. Coolant actually becomes corrosive over time, accelerating the wear on the cooling system!

Not only the correct coolant type but also the correct mixture is important. Such errors will not only decrease the cooling efficiency due to mismatch in the heat-carrying capacity of the coolant but also the variation in density will hamper the pump functioning and vary the speed of mass flow rate of the coolant in the system.

  1. Cavitation

Why Cavitation in Pumps Occurs

The tiny “bubbles” of water pump cavitation can kill the pump. While you will never actually see the tiny bubbles of cavitation in pumps, you can see the damage of cavitation that looks like metal eaten by termites.

That is because these do not really bubble you see when it comes to the cavitation in pumps — they are voids. Inside these tiny voids is a super-heated vapour that can erode metal and crack the plastic. Cavitation in pumps is not typically the fault of the water pump itself, it is only the victim of other problems with the coolant and other components.

The voids of water pump cavitation are generated by the movement of the pump’s impeller against the coolant. There are two types of pressures that determine if cavitation in pumps will occur. The first is the vapour pressure that is related to system pressure. The second is the pressure and suction generated by the pump.

If you remove the radiator cap from a hot system, the coolant is suddenly above its vapour pressure and steam is formed. The same thing can happen inside the water pump. As the impeller spins, its coolant is pushed in one direction and pulled in the other by the blades. If the negative pressure is great enough, voids are formed. Inside the voids is super-heated steam that can cause damage to the impeller and housing.

Coolant Condition and Cavitation in Pumps

The condition of the coolant has a direct relationship to cavitation in pumps. The specific gravity of the coolant depends on the dilution of the coolant with water. If the specific gravity is too high, it will change how the pump operates.

Up to a 70% mixture of antifreeze can be used in extremely cold climates to lower the freezing point of the coolant, but the trade-off is reduced cooling efficiency because ethylene glycol carries heat less efficiently. If the concentration of antifreeze to water is too high in hot weather, it may increase the risk of the engine overheating and make cavitation in pumps more likely to occur.

The coolant additive packages contain wetting agents or surfactants that reduce surface tension and allow the coolant to transfer heat more efficiently. Diesel coolant includes additives that prevent water pump cavitation erosion around the cylinder liners.

New coolant includes buffers that can control the pH. Cavitating acidic coolant is even more damaging to plastic composite impellers because the vapour is now acidic.

Water Pump Cavitation Culprits

The health of the overall cooling system can contribute to water pump cavitation. If a system is not able to transfer heat effectively, it will cause hot spots and increase the pressures in the system. Also, leaks in the system can cause cavitation in pumps because the vapour point of the coolant is lower due to the lack of pressure. This is why pressure testing is important.

Restrictions in the system can cause pressure and suction changes that can lead to water pump cavitation problems because how the coolant flows over the impeller has changed. Restrictions can be caused by a collapsed hose or a clogged radiator. Installing a new water pump on a system with a restriction can limit the life of the new pump.

Signs of Cavitation in Pumps

There are no outside visual clues of water pump cavitation. The typical symptoms will be overheating and possibly leaking from the weep hole of the water pump. In some cases, the impeller will separate from the shaft. It is not until you remove the pump that the full extent of the damage is revealed.

Cavitation in pumps can attack not only the water pump but the part of the housing that is contained in the block, front cover or cylinder head. These problems must be addressed if the new pump is going to last.

  1. Stagnation of Air

The cooling system will not perform satisfactorily if the amount of air that has to reach the radiator is not sufficient. This can be due to several reasons. This can be due to the incorrect positioning of the radiator, unclean air reaching the radiator, turbulent air reaching the radiator or incorrect fan choice.

Incorrect positioning of the radiator – Usually in the vehicles the radiator is placed in the front of the vehicle so that the radiator receives fresh air and at the maximum -possible speed. But due to the front grill or any other covering, this air can be restricted. In cases where the radiator is not placed in the front, this issue can be much greater.

Incorrect Fan – while replacing the fan from the manufacturer provided OEM, some people go for the locally available cheaper options. But at the time the specifications do not match. Either the fan is not capable of providing the high cfm of air or at a tie, the performance of the fan causes stagnation of air in the operational region of the system. Hence the air provided to the radiator will be affected and thus affecting the overall performance of the system.

  1. Faulty thermostat

One of the most common reasons that your engine may overheat is due to a malfunctioning thermostat – but the thermostat inside your car is rather different from the one in your house. In your home, your thermostat keeps track of the temperature and triggers the heat or air conditioning system to turn on, depending on its settings. But if your house gets too hot and nothing happens, you’ll notice and open some windows, turn on fans, or take other steps to fix the problem, even if you have to wait for a repairman.

When your engine gets too hot, however, you can’t do anything to remedy the problem. That’s because your engine thermostat is actually a valve that controls the flow of coolant. When the engine gets hot, the valve opens and coolant flows through to reduce the engine temperature, while a cool engine has a closed valve that blocks the flow of coolant and helps a cold engine warm-up.

A broken thermostat might be stuck in the closed position, causing the engine to warm up – and then keep going. No matter how hot the engine gets, the coolant is unable to pass through. This is a real problem and can cause your engine to overheat rapidly.

Reference

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