Coolant Maintenance


The performance requirements of automobile antifreeze became more severe during the

1980’s and 1990’s. The reduction of the overall mass of vehicles to improve fuel

economy entailed extensive use of light materials such as aluminum and plastics for the

construction of engine and cooling system parts. Many of the engines used today in

most forklifts use aluminum heads and, in some cases, aluminum engine blocks. The

volume of antifreeze used was also drastically reduced to further reduce weight,

subjecting the antifreeze to high rates of flow, high temperatures and significant metalto-

coolant heat fluxes. Today’s smaller, efficient and powerful engines dissipate more

heat, requiring that the antifreeze keep the heat exchange surfaces in clean condition. In

addition, corrosion, which in itself is of concern, can also result in heavy corrosion

deposits that impede heat transfer.

Modern antifreeze provides year-round protection of the cooling system: It prevents

freeze up in winter and boilover in summer. It provides protection from rust and

corrosion and does not harm rubber hoses and plastics. A desirable antifreeze should

not corrode metal parts, attack rubber, become viscous at low temperatures, or

evaporate readily at the ordinary engine operating temperature. It should be chemically

stable, a good conductor of heat, and a poor conductor of electricity (which causes


There are basically three types of antifreeze, and all of them are made from 95% or

more ethylene glycol. That means that all three types will mix without causing the

buildup of sludge in the Cooling System or clogging your radiator. But mixing the

various antifreeze versions can reduce the supplemental coolant additive package

(SCA) to its lowest level of corrosion protection. Engine Coolant should be Anti-

Freeze mixed 50/50 (or close to it) with water in order to achieve the highest degree of

protection against freezing and boil over and it also protects both the engine and heat

exchanger (radiator, heater core, or intercooler) from corrosion. Generally if the engine

coolant is more than 70 % antifreeze it loses its corrosion protection and heat transfer

capability. CLARK  (in particular) DOES NOT APPROVE the use of straight concentrated

antifreeze as engine coolant. The corrosion that we are all worried about is generally

either corrosion of aluminum or corrosion of the lead in the solder of copper-brass


The first, oldest, and most familiar type of antifreeze is known as “Conventional

Green” and is a good general antifreeze with protection for both aluminum and solder.

But it has Inorganic Acid Technology, (IAT) for additives, and tends to get corrosive as

the coolant ages. The standard practice has always been to change your engine coolant

once a year and flush the engine cooling system to get rid of the contamination that has

settled out of the coolant and into the cooling system. If the engine cooling system is

not serviced as recommended you will end up with corroded radiators, corroded engine

parts, overheating problems, and various other engine problems.

The second type of antifreeze is a long life antifreeze and uses DexCool as bases for its

SCA package. The DexCool is orange in color and this additive package is known as

Organic Acid Technology (OAT). The DexCool SCA package deteriorates more

slowly and is less aggressive against aluminum; BUT it is much more corrosive against

the solder in copper brass radiators. A few lift truck manufacturers are using all

aluminum cooling systems so DexCool does not pose problems. But some still use

soldered copper brass radiators, this bring us to a second generation of DexCool known

as Hybrid (HOAT), or G-05. The hybrid (HOAT) G-05 had some of both the IAT and

OAT and is the most prevalent automotive OEM initial fill (yellow in color). There is

also an Asian version of the hybrid (HOAT) G-05 antifreeze that is pink and has some

phosphate additives.

The third type of antifreeze is known as Pre-Charged Heavy Duty and is the coolant

used in Heavy Diesel engines with a tendency toward liner pitting. It is available as

either conventional IAT (green) or Extended Service OAT which is red in color. It has

an additional “SCA package” of additives that prevent iron corrosion, aluminum

corrosion, and solder corrosion. Also, when it does degrade it is not as aggressive as

the IAT green kind.

Regardless of what antifreeze you are using you still must keep the engine cooling

system filled with non-aerated coolant. Failure to do so will cause overheating

problems and will also cause any contamination in the engine coolant to solidify and

drop out and clog the cooling system.

When the Engine Coolant is low it is  recommend to use a manufacturer pre-mixed

50/50 solution that doesn’t require diluting and comes from the factory with de-ionized

water. If a factory pre-mixed solution is not available fill the cooling system with

mineral free water that does not contain any salts, mud, rust, lime, or other




Deteriorated coolant or coolant unsuitable for use in engines having aluminum alloy

components corrodes the surface of the aluminum, known as the aluminum matrix, on

the inner surface of the water chambers. Silicon crystalloids (Si) stick out in the

corrosion layer and increase the corrosive action on the aluminum matrix, this results in

a selective etching of the aluminum matrix in that particular area of the water chamber.

The higher corrosive action of the etched area increases the number and depth of the

corrosion pits, which eventually leads to a fatigue failure of the aluminum matrix

resulting in a crack in the water chamber. The selective etching and ultimate crack will

be initiated in an area of the aluminum matrix that has a higher concentration of stress.

In addition, the deteriorated coolant will also cause corrosion in the solder joints of the

radiator by disassociating the lead from the solder; it may also cause bimetallic

corrosion with any lead-aluminum alloy in the radiator. In either case the end result

will be either cracks or leaks in the soldered joints of the radiator, or decreased cooling

efficiency of the radiator due to restrictions caused by the corrosion.


SOLUTION: Proper Cooling System Maintenance is especially important to replenish the additives

that protect the cooling system from rust, corrosion, pitting, electrolysis and foaming to

aid in the prevention of these issues.


1) The Engine Coolant level and condition be checked at every PM after the

Engine has cooled down:

A.) First check the Coolant Level in the Radiator and make sure the

Radiator is completely filled, if necessary bleed the Cooling System in

accordance with SI-01-818-10.

B.) Then fill the Recovery Bottle so the Coolant Level is between the Cold

and Hot Fill Lines.

2) The Engine Coolant protection and additives be checked at every 1,000

hours or six months of operation. The Engine Coolant System be drained

and flushed, and the coolant changed a minimum of once every 2,000 hours

or one year of operation, maintaining the proper concentration of the

Antifreeze/Water Solution.

3) In addition most recommend the Radiator Cap be inspected at each

PM, and Pressure Tested a minimum of once every 2,000 hours or one year

of operation, or more often if required.


As the additives (SCA’s) in your coolant that keep it neutralized become depleted the

coolant actually develops an electric charge from passing over dissimilar metals. This

small electric current removes metal from engine surfaces leaving large pits or holes

and can eventually eat entirely through a component. It can also weld bolts and

fittings to the engine and components. A Digital Voltmeter can be used to test the

strength of SCA Package in the Engine Coolant:

1) Set the Digital Voltmeter to read at the lowest DC Voltage Setting.

2) Attach the Digital Voltmeter Negative (-) Probe to the Negative (-) Battery Post.

3) Insert the tip of the Digital Voltmeter Positive (+) Probe into the coolant and

observe the reading.

4) If the Digital Voltmeter registers:

0.10 – 0.19 Volts – The engine coolant SCA package is still good.

0.20 – 0.24 Volts – The engine cooling system should be schedule to be

drained and flushed, and have the Antifreeze replaced.

0.25 or greater Volts – The engine cooling system should be drained and

flushed, and have the Antifreeze replaced immediately.



Some Lift Trucks are delivered with a Traditional Ethylene Glycol Antifreeze /

Coolant in the Engine Cooling System. The Traditional Ethylene Glycol used by

CLARK, is a low silicate formulation based (IAT Technology) Antifreeze/Coolant,

usually green in color, that is suitable for light trucks and heavy duty vehicles, and also

protects all engine cooling system metals from corrosion including aluminum. Many

recommend servicing the Engine Coolant / Cooling System as described previously in

this Service Bulletin.

When servicing the engine cooling system many recommend using the Pre-

Charged Heavy Duty 50/50 Premixed Antifreeze (red in color)

which is a gallon container. It is extremely important that the engine

cooling system be flushed with Super Flush and

thoroughly drained before refilling the system with the Pre-Charged Heavy Duty 50/50

premixed Antifreeze. Using the Pre-Charged heavy Duty Antifreeze should

dramatically reduce engine cooling system maintenance.

As a minimum, the Antifreeze/Coolant to be used in Lift Trucks must meet or

exceed the following specifications and /or recommended practices:


ASTM D3306 GM 1899M Cummins 90T8-4

ASTM D4985 GM 1825M TMC of ATA RP-302B

SAE J814c Ford ESE-M97B44-A Federal Specification A-A-870A

SAE J1034 Chrysler MS7170 Clarke – Approved

SAE J1941 Detroit Diesel 7SE298




Appearance Fluorescent Green

Specific Gravity 60/60°F 1.130

Freezing Point (ASTM D1177), 50% Volume, q.s.

aqueous solution


pH (ASTM D1287), 1:2 dilution with water 10.5

Reserve Alkalinity (ASTM D1121) as received 12.0

Silicate (as Anhdyrous Alkali Metasilicate) 0.09%