Keep your cool – Professional cooling system advice.June 26, 2018
The components of a cooling system can only do their intended job when proper service is employed. Often, the efficiency is compromised due to incorrect water pump belt tension, corrosion or flow restrictions (liquid or air) and a weak pressure cap (each psi raises the boiling point three degrees F). This primer will address the less known service steps for a cooling system. Basics such as belt tension and radiator cleanliness will be assumed.
Get the air out
The job of the coolant is to remove heat from the engine and that of the radiator is to cool the liquid.
A common issue is an air bound cooling system. A liquid cooling system follows the laws of hydraulics in regard to coolant flow. The coolant must come in contact with the parts that need to be cooled and touch the tubes of the radiator to allow the temperature to be dropped. If there is any air in the system both of these functions are diminished drastically.
The hallmark of an air bound cooling system is a temperature gauge reading that swings from hotter than normal to colder than normal. This can happen over a matter of time as little as 30 seconds to as long as a few minutes. The system is usually greeted with a like swing in heater output, from very hot to very cold.
The heater and temperature gauge fluxuations are caused by air pockets in the coolant. When an air pocket or bubble hits the temperature sending unit, there is no heat transfer to it, so the gauge swings to a cold reading. Likewise, when air is pushed through the heater core which is a small radiator, no thermal transfer takes place and the discharge temperature drops in the cab. When the air pocket moves away and liquid is introduced the coolant starts to boil and thus, the temperature gauge registers this and the heater output becomes very hot.
Bleeding a cooling system is not a difficult task but it can be time consuming.
The radiator should be filled to about one-half to one inch below the top of the neck and all of the tubes should be covered. A supply of coolant should be kept handy. As air is displaced the liquid level will drop. Start the engine and run at a fast idle of around 1,000 rpm. If equipped, the heater should be turned on to “full hot” but the fan speed is not critical. The high idle speed is required to increase the flow rate of coolant through the system and push out the remaining air. It is necessary to turn the heater on to allow the air to be removed from that circuit of the cooling system.
At this time the thermostat will be closed and will start to open as temperature is built. As this occurs the coolant level will drop and need to be topped off to keep the radiator full and not introduce any additional air.
As the coolant heats it will expand and want to push out of the radiator creating a mess and the need for a proper clean up. To eliminate this an excellent tool is the Lisle Radiator Fill Kit that allows a funnel-like reservoir to be attached and eliminates coolant spillage during expansion.
As the engine is run at high idle the coolant level will eventually stabilize but your job is not done. You will need to monitor the fluid for any signs of air bubbles. These may be very large and obvious or inconsistent small bubbles. Be patient. Allow all of the air to work out.
Understanding and recognizing electrolysis
Electrolysis occurs when electrical current routes itself through the engine’s coolant in search of a ground path. Current can be introduced into the cooling system in many ways but the two most common causes are a poor ground from the starter motor and the engine block to the battery.
Electrolysis is a fast-acting problem that attacks not only the heat exchangers in a tractor or farm vehicle but can destroy an entire engine in as little as a few thousand hours, based on industry data. A small amount of measurable voltage can be detected in most cooling systems from a reaction between the coolant and system metals. The value should never exceed a tenth (1/10 or 0.10) volt. Older-style (copper/brass) cooling systems can tolerate higher stray voltages, as much as 3/10 volt, but this would be considered excessive and point to an issue elsewhere.
Electrolysis occurs when a defective or missing ground causes the electricity to seek a path of least resistance. Sometimes the path is a coolant hose or the radiator or heater core.
A poorly grounded engine and starter motor can put enough current through the cooling system to actually cause a heater core or radiator to come apart in a matter of months. This would be dependent on how often the engine was started since the current would only pass through the coolant during crank.
Evidence of electrolysis includes unexplained and or recurring pinhole leaks in a radiator, heater core or even aluminum intake manifolds. Pinholes may form anywhere along the tubes or tank walls, but damage is often concentrated at the tube-to-header joints, or in the tube walls near the center of the core.
All that is required to test for this is a voltmeter. Connect the negative lead to the vehicle battery negative terminal and submerge the positive lead in the radiator making sure it does not touch anything. Perform several tests under various conditions such as key on-key off, engine running at high idle speed, electrical accessories activated, etc. If zero volts are detected there is no problem and you can confidently state electrolysis is not present.
If any stray voltage is found it is important to perform a second test with both battery cables disconnected. For this procedure connect the meter in this manner: negative lead to a very clean and unpainted area of the engine block or to the disconnected negative battery cable; positive meter lead submerged in the engine coolant. Do not touch any metal with the lead. Make sure the disconnected battery leads do not touch each other or any other part. It is a good idea to insulate them with some clean shop rags or electrical tape.
If voltage is detected with the battery disconnected the cooling system is contaminated and must be flushed clean. With the battery disconnected the coolant voltage should be zero. If it isn’t the following could be the cause: depleted coolant additives, over diluted coolant, metallic sludge in the system, acidic coolant, make-up water containing chloride (salt from a water conditioner). This is the result of a chemical reaction in the engine between the dissimilar metals, corrosion and coolant that created a weak battery.
Internal hose degradation
Contrary to what many think a hose does not deteriorate from the outside in but from the inside out. The only time external wear will overtake internal degradation is when the hose is soaked in oil from an engine leak or is rubbing against something and is worn through.
Electrochemical degradation (ECD) occurs when the coolant becomes acidic from the additive package being consumed and depleted over time. ECD causes micro-cracks within the hose tube that allows the coolant to attack the hose reinforcement. Over time this weakens the yarn material that makes up the reinforcement of the hose. Accelerated by temperature and constant movement, ECD produces a pinhole leak and will cause the hose to burst before it has reached its expected life cycle.
ECD cannot be detected visually with the hose on the engine but can usually be identified by squeezing the hose to determine if it feels very squishy or extremely hard. Also, be on the look out for bulging at the ends where the hose connects to the engine and radiator. If any of these conditions exist the hose and thus, the reliability of the equipment are in question.
Hoses injured from thermal cycling will usually have a hardened, glossy appearance with surface cracks showing on the outside. On the inside the interior yarn fiber may be damaged, causing the coolant hose to feel soft in places. A hose in this condition can burst without notice.
Service life of anti-freeze
Anti-freeze does not loose its ability to not freeze but over time the additives and anti-corrosion inhibitors become neutralized or worn out. When this occurs the coolant no longer provides the necessary protection required for long engine and cooling system component life. For this reason, all coolants are considered consumable and eventually need to be replaced or have the additive package renewed with a bottle of supplement (SCA).
On larger diesel farm equipment, test strips can be employed to confirm the additive package. Depleted additives not only promote corrosion but cavitation (air bubbles) that can destroy the cylinder liner in the engine block.
With a smaller capacity cooling system, it is more prudent to just change the coolant with the engine manufacturer recommended type every two to three years.
Engine coolant will degrade quicker under severe duty and high thermal loads. This is a result of the normal boiling that is occurring in the engine around the exhaust valves. In addition, all coolants will absorb moisture even though the modern cooling system is identified as a “closed” design. Humidity gets wicked into the coolant through the overflow/expansion tank and from the radiator cap seal when the engine is at rest.
Checking the freeze point does not tell you that the additive package is good.
The most common anti-freeze testers use either a needle or a series of balls to determine the temperature at which the coolant will freeze. Most if not all of these testers are designed to check coolant at 60 F degrees. Liquid temperature colder or hotter than this will skew the readings.
The most accurate method to check the coolant’s potency is to use a refractometer. This is a device that measures the sample’s refractive index of light when subjected to the test liquid.
What it all means
The best method to maintain the system is a good preventive maintenance (PM) program. The installation of new, fresh coolant every three years will always be the best way to guarantee long engine and component life and not experience a failure in the field.
Anti-freeze should be mixed 50/50 water and coolant. This will provide the best freeze and boil-over protection. Tap water should not be used due to its impurity. Distilled water needs to be employed. It is the easiest and most cost effective to purchase already mixed 50/50 name brand coolant — this eliminates all concerns.
With a little care the cooling system will go about its job silently. Miss any one of these steps and the system will become your worst enemy in the field!