Monday, July 15, 2024 Detailed Auto Topics
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The automotive cooling system is one of the most problem prone components of a vehicle

The system is complex while giving the outward appearances of simplicity. This is why cooling system repairs account for a huge percentage of total repair dollars spent. Like many other things, most of the repairs are preventable.

Early symptoms of cooling system problems often show up as leaks. Leaks are symptoms, because there is normally a more involved root cause. Simply replacing a leaking component results in the symptom returning, often in the same area. For instance, a heater core is found to be leaking. We replace, and three months later it’s leaking again. Bad core? Replace it again and two months later the radiator begins to leak. Next an intake gasket may start to leak, followed by the water pump.

The leak is merely a symptom of the problem. The problem is normally corrosion, often caused by improper service procedures. While the cooling system in a modern vehicle may resemble those in the 1990's models, they are quite different.

  1. Extensive use of aluminum and other active materials is common.
  2. The coolant is normally not a silicate or phosphate type, rather organic acid technology (OAT) or hybrid organic acid technology (HOAT.)
  3. Change intervals, while longer, are far more critical.
  4. The method of mixing coolant is critical.
  5. The engine is mounted higher than the radiator and many cooling systems do not self-bleed.
  6. Extensive use of electrical components, add potential for electrolysis.

Engines use a variety of materials

The cast-iron construction of the past is largely gone. Most modern vehicles have aluminum cylinder heads and plastic intake manifolds.  Radiators are aluminum and plastic.  Cylinder blocks may be iron or aluminum and some have iron or steel cylinder liners. These materials all expand at different rates. No longer are gaskets static seals. More often they are a series of O-rings, held in place by plastic backings. This allows for movement as the components expand and contract. It also requires perfectly smooth surfaces on which to operate.  Rough machine work on the heads and intake are common.  A rough finish will greatly increase the chances of a problem.  On engines with known intake gasket problems, cooling system maintenance is even more critical.

OAT and HOAT coolants

The surfaces on which the seals operate are exposed to coolant. With OAT and HOAT coolants they are protected by an etching process and a coating produced by the coolant In time, coolant loses its ability to protect the metal. When this happens, corrosion quickly pits the metal, and a leak develops Worse,leaks allow air to enter the system and the effect is greatly multiplied. Unprotected aluminum, exposed to a corrosive liquid and in the presence of oxygen will be destroyed in very short order.

Adding water to the leaking system further dilutes the corrosion protection. This dilution speeds the corrosion process. This is particularly true if non-distilled water is used. Tap water often contains minerals, silica, chlorine and fluoride, all of which can add problems to the system. Water should never be added to a cooling system. Instead, either pre-mixed coolant or concentrated coolant, mixed with distilled water should be used. Pre-mixed coolants are already blended with distilled water and in the proper amounts. When using a concentrate, mix it in a 50/50 blend, with distilled water, before adding it to the system.

Change intervals

Modern long-life coolants can provide years of service. GM claims their Dexcool product will protect for five years. This claim seems to be predicated on time till 100% depletion of the corrosion protection. While the coolant may still look okay at five years, great damage may be occurring due to corrosion. It is imperative that this coolant not be pushed beyond the recommended service life. It is also suggested that five years only applies to the initial fill in the new vehicle. Subsequent fills offer shorter term protection.

A great many problems are actually created by improper change procedures. Using non-distilled water as mentioned. Using the wrong coolant is another problem. Each coolant type has its own protection strategy. Mixing coolants or using the wrong type can drastically effect protection.

Small sample of extended life coolants in current use

Coolant must also be precisely mixed in order to protect the system. The water in the mix cools the engine. The coolant protects from freezing and corrosion. With too much coolant, cooling will suffer. With too much water protection is greatly decreased. The mixture needs to be precisely maintained..

% AntifreezeFreeze Point Fahrenheit


25 degrees F


16 degrees F


10degrees F


4 degrees F


-3 degrees F


-12 degrees F


-22 degrees F


-34 degrees F


-48 degrees F


-62 degrees F

A 50/50 coolant and distilled water mix is normally required.  When replacing coolant, it is important to remove all the depleted coolant from the system.  Simply draining the radiator may leave up to 50% depleted coolant in the engine block, heater core and hoses.  Adding fresh coolant mix to a system that still retains depleted coolant results in protection that is greatly diminished.

The coolant and distilled water must also be premixed, before pouring into the radiator. Because coolant is much heavier than water, it will settle to the bottom of the engine. Water that is added after the coolant will not mix.  This vastly disturbs the corrosion protection and can cause hot-spots in the engine. Pre-mixed coolant is very good for this purpose, though it is considerably more expensive than concentrate.

Engine air bleeding

Engine coolant bleed screw for purging air from system

Because of styling constraints, most engines sit higher than their radiator. When a system is drained air enters. When the system is filled, air rises to the highest point. In older vehicles this was the radiator, so the systems would self bleed. Newer systems often have an involved bleeding procedure that must be closely followed. Failure to bleed the system can result in overheating and corrosion to the system.

Service procedures that can damage the cooling system

  • Not draining all depleted coolant
  • Failing to pre-mix distilled water and coolant
  • Adding different types of coolant to the system
  • Topping off a leaking system with tap water
  • Not bleeding the system

Electrolysis and the electrical factor

Electrolysis occurs when the engine lacks a proper ground for the electrical system. For example, when a temporary battery end is improperly used to repair a corroded cable. This can provide an inadequate ground. If the engine requires 130 amps to operate and the ground can only conduct 100, the additional power can be pulled through the coolant. This is because the engine block is isolated from the ground by the rubber mounts.

Electrical current flowing through coolant can produce an anode/cathode type effect. The thin aluminum of the radiator and heater core will quickly be eaten away. In extreme examples, cylinder heads and even cylinder walls can be destroyed. Electrolysis is difficult to detect and often does huge damage before being uncovered.

Electrical cooling fans add to the problem. They produce a large electrical draw, right in the area of the radiator. It is imperative that all electrical grounds be in place, clean, tight and working properly. Grounding problems are almost always the result of improper previous repair.

Cooling system work has changed drastically over the years. Unfortunately, many shops and do-it-yourselfers have not kept up. Be certain to use only a qualified shop such as AGCO Automotive or be thoroughly familiar with the technology. Improper cooling system service is a VERY costly mistake.

For even more information on cooling system, Dexcool and mixing coolants, see our Detailed Topic, Dexcool, coolants and proper service.

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