Over the last several months, Mopar Connection Magazine has reviewed cooling systems (stories one, two, and three). This month, we will complete our coverage by examining antifreeze, water, mechanical and electric water pumps, hoses, and thermostats.
Chrysler has used a variety of engine coolants over the decades, with changes driven mainly by evolving engine materials, emissions regulations, and coolant technology. The following is a breakdown of the main types of coolant used in Chrysler products over the years.
Above: After several decades of minimal changes to the cooling system layout, the last thirty years have seen significant advancements in thermal management systems. The Hemi (left) had a mechanical water pump, two radiator hoses, and a pair of heater hoses. The Wrangler 4xe (right) has a crowded engine bay with a cooling system that includes radiator hoses, a degassing tank, multiple heater core hoses, coolant valves, and mechanical and electric water pumps.
From the late 1940s to the mid-1990s, Inorganic Additive Technology (IAT) coolant was used in Chryslers, Dodges, Plymouths, DeSotos, Imperials, Jeeps, and other Mopar products. It was bright green and had service intervals of two years or 30,000 miles.
The traditional formula used silicates and phosphates for corrosion protection. It was compatible with older cast iron blocks and copper/brass radiators. IAT (ethylene glycol) is still available as a conventional green coolant and is required for many classic Mopars.
Above: All the vintage Mopars cooling systems until the mid-1990s came equipped with Inorganic Additive Technology (IAT) coolant. IAT, also known as ethylene glycol, is a green coolant. Multiple companies have blends of IAT coolant in a 50/50 mix and a concentrate. The 50/50 mix comes with antifreeze and water, ready to install into a vehicle. Concentrate requires mixing, and the water used at your site may be unacceptable (hard water, minerals, etc.). IAT coolant is high in silicates and phosphates to provide corrosion protection for the cast iron cooling system components.
Ethylene glycol’s history started in the 1920s when it was introduced as an automotive antifreeze and coolant. In 1926, it was presented as a safer alternative to volatile and toxic methanol-based antifreeze. It was branded and sold under names like “Prestone,” launched in 1927. By the late 1930s, ethylene glycol had largely replaced earlier antifreeze formulations (like salt brine or alcohol) due to its superior boiling point, lower freezing point protection, and reduced instability.
The addition of ethylene glycol to water greatly lowers the liquid’s freezing point, down to -40°F or lower when mixed 50/50 (antifreeze/water). It raises the boiling point protection to around 220°F and higher with radiator pressure caps. IAT is less prone to evaporation than methanol. Corrosion inhibitors were added, especially in the 1940s and 1950s, as engines began using more aluminum and other reactive metals.
Hybrid Organic Acid Technology (HOAT), an orange or reddish-orange-colored coolant, was introduced in the mid-1990s and used until around 2012. The service interval for HOAT is five years or 100,000 miles. Besides Mopar OEM 50/50 mix part 68051212AB and OEM concentrate part 68048953AC, Zerex G05 (50/50 or concentrate) is the same coolant. HOAT has a mix of silicates and organic acids. It was designed for longer life and better aluminum protection.
Above: Chrysler switched to Hybrid Organic Acid Technology (HOAT), an orange or reddish-orange coolant, in the mid-1990s. HOAT had a reduced mix of silicates and additional organic acids. The newer coolant had extended service periods and better protected aluminum components. Again, it can be purchased in a 50/50 mix or a concentrate.
Above: Plenty of aftermarket coolant manufacturers make acceptable HOAT coolants for Mopar products built between the mid-1990s and 2012. The coolant’s service life is rated for five years or 100,000 miles.
From 2013 to date, Organic Acid Technology (OAT) has been used in most Chryslers, Dodges, Jeeps, Ram Trucks, and Fiats since the FCA merger. The coolant is pink or purple; the Mopar OEM 50/50 mix part number is 68163849AB, and the OEM concentrate part number is 68163848AB.
The interval of the service is ten years or 150,000 miles. OAT is silicate and phosphate-free and designed to provide maximum cooling performance for modern engine materials. It is not backward compatible with older HOAT or IAT systems without a full flush and change of gaskets and hoses if needed.
Above: In 2013, Chrysler transitioned to Organic Acid Technology (OAT) coolants for most vehicle lines. OAT, pink or purple colored, is a silicate and phosphate-free coolant designed for multiple materials found in late-model engines. Again, it is available in a 50/50 mix or concentrate. The coolant has a ten-year, 150,000-mile service life.
Lastly, the limited-use, Asian-influenced blue (or turquoise) coolant was used in imported Chrysler vehicles or rebadged models (Mitsubishi-based models or FCA/PSA global platforms). The coolant recommended varies because it is typically not factory-filled in North American cars unless sourced from a worldwide partner.
A couple of notes about coolant: never mix coolant types because chemical reactions can cause gel/sludge. Referring to the owner’s manual or coolant reservoir label in the engine bay is best. If restoring a classic Mopar, use green IAT coolant or a phosphate-based alternative. Lastly, for modern Mopars (2013+), only use Mopar OAT or equivalent.
Above: When the manufacturers added water pumps to engines, the pumps all had a belt-driven design. A belt riding on the crankshaft pulley and water pump pulley spun the water pump at a ratio (depending on pulley diameters) of the engine’s RPM. Cooled coolant from the radiator entered the housing (left), and the pump (right) impeller would sling the coolant outward against the housing. The coolant would be forced out of the housing into the water jackets of the block or heads.
When mixing antifreeze with water, what water should be used? Distilled water is the most acceptable, but some applications call for deionized water (low conductivity for hybrid and EV applications). Others may call for de-mineralized water. Yet even some coolants have no water at all—Evans Waterless Coolant. It is best to follow the manufacturer’s recommendations.
Over the decades, Chrysler has used various mechanical and, more recently, electric water pumps across its vehicle lines. The evolution of these systems is closely tied to changes in engine design, emissions requirements, fuel economy goals, and the use of hybrid technology. The water pump (regardless of design) circulates the coolant through the engine, radiator, and heater core, or the electric motor, inverter, electronics, and heater core (if equipped).
Above: Water pumps come in all different shapes and sizes, but they all perform the same function—moving coolant. The pulley attaches to the shaft (left – four silver bolts), and as the belt rotates it, the impeller (right – silver star shape) on the opposite side of the shaft rotates, moving the coolant through the pump and into the engine.
Mechanical water pumps are driven by an engine accessory belt (serpentine or V-belt). They are centrifugal pumps designed with an impeller. The housings are cast iron, aluminum, or stamped steel and have a rubber or ceramic shaft seal. Mechanical pumps have been used in production engines since the 1920s.
The mechanical water pumps were installed on all the slant-6, LA/Magnum V8s, B/RB big blocks, and 426 Hemis (cast iron or aluminum bodies). Modern pushrod engines like the 5.7-, 6.1-, and 6.4-liter 3 Hemis (use aluminum mechanical pumps), and front-wheel-drive 4-cyl and V6s (2.2-liter Turbo, 3.3-liter, and 3.8-liter) often with water pumps integrated behind timing covers.
Above: While still a mechanical centrifugal pump, the water pump drive pulley is driven by an electric motor. The water pump speed is no longer dependent on engine RPM. The electric drive motor is sufficient for drag racing purposes. Although it operates at a fixed RPM and is not pulse-width modulated (varying the voltage to the pump), it can be run as part of the post-engine cool-down process.
Although a robust design, mechanical water pumps have weaknesses. The shaft seals may leak due to age and lack of cooling system maintenance. Additionally, the water pump impellers will corrode, and the pump may fail due to bearing wear or coolant contamination.
The crankshaft does not drive electric water pumps (EWPs). Instead, the EWP is controlled (commanded) by an electronic control module (ECM) or a thermal management module. The advantages of an EWP are variable flow control, better warm-up times, and reduced parasitic losses. Since 2007, EWPs have been used in hybrid and turbocharged factory engines, high-performance applications, and fuel economy-optimized platforms.
Above: With the introduction of electric vehicles and hybrids, electric water pumps (EWPs) have moved to the forefront to provide motor and inverter cooling instead of or independent from an internal combustion engine. The pumps are computer-controlled, and the RPM can be controlled via pulse-width modulation.
Hybrid models using EWPs include the Chrysler Pacifica Hybrid and Jeep 4xe (Wrangler and Grand Cherokee). They use auxiliary electric pumps for cabin heating and battery thermal management. The late-model 2.0-liter turbo I-4 found in the Jeep Wrangler and Alfa Romeo Guilia uses an electric pump. The 6.2-liter Hemi in the Hellcat, Demon, and Redeye use auxiliary electric pumps for intercoolers and charge air coolers.
Due to weather pack failures, EWPs can suffer from corrosion concerns at the electrical connectors. Control modules can fail. The motor can burn out after years of service. Most centrifugal motors are non-serviceable, and scores of EWPs are also non-serviceable, which necessitates a complete replacement when a failure occurs.
Above: Spring-type hose clamps were popular in early Mopars and the muscle car era. The spring metal held the hoses firmly in place, whether on the radiator, water pump, thermostat housing, or heater core.
Radiator and heater hoses are essential components in Chrysler vehicles (and all internal combustion engines), serving as the flexible plumbing for the engine’s cooling system. The upper radiator hose carries hot coolant from the engine to the radiator for cooling. The lower radiator hose returns cooled fluid to the engine from the radiator. Heater hoses carry hot coolant from the engine to the heater core and return cooler fluid from the heater core back to the water pump or radiator.
From the 1950s to the 1970s, Chrysler products used reinforced rubber (Ethylene Propylene Diene Monomer (EPDM) or nitrile) hoses, oftentimes with cloth or spiral reinforcement. Hoses were often molded or pre-bent to fit big-block, small-block, or slant-6 applications. Hose clamps were typically tower-type, spring-wire type, or worm gear clamps.
Above: After the late 1970s, the manufacturers moved to worm-style hose clamps (and other designs of spring-type clamps). Owners often used the worm-style clamps to substitute the spring-type clamps found on earlier models when the hoses were replaced.
During the 1980s through the 1990s, materials improved for higher operating temperatures and pressures, and plastic or composite quick-connects began appearing on heater hose fittings. Late-model vehicles continue to be fitted with EPDM hoses or, in higher-end models, silicone rubber hoses. The hoses are pre-formed with integrated plastic connectors and bypass valves. Most of the complexity of the hoses is found with the heater hoses. The heating system may include a series of quick-disconnect assemblies or integrated metal tubes.
The typical lifespan of radiator and heater hoses is approximately ten years. Swelling, soft spots, leaks, and cracks are signs of failure. The life span of hose clamps varies, but rust, loss of tension, and leaks under pressure are all signs of failure.
Silicone hoses are used for high-dollar applications because they are more durable and heat resistant. Reinforced Kevlar or braided hoses for racing are also common. Lastly, AN-style fittings for custom setups provide threaded hose ends for quick removal and reinstallation.
Above Left: Quality radiator hoses come pre-formed for the application in which they are installed. The proper contours allow the coolant to flow smoothly without bubble-forming turbulence found in universal flexible hoses. On Mopar small blocks, there is a pre-formed bypass hose. Above Right: The heater hose is purchased by the foot. It comes off a roll and is a trim to fit for each application’s design. The heater hoses should be replaced at the same intervals as the radiator hoses. Slant sixes use a segment of heater hose for the bypass hose.
An engine thermostat is a temperature-sensitive valve critical in regulating engine temperature and controlling coolant flow in internal combustion engines. The thermostat ensures the engine warms up quickly after startup and maintains optimal operating temperature (typically around 190 to 225°F).
The wax pellet element thermostat is the most common. It has a sealed chamber filled with wax that expands at a set temperature. As the wax swells, it pushes a rod or piston that opens the valve. When the engine cools, the wax contracts, and a spring pulls the valve closed again.
Above Left: Thermostats allow the engine to warm up quickly when closed and maintain the coolant temperature once opened. A thermostat prevents overcooling but not overheating. Above Right: Many, but not all, thermostats have a jiggle pin (check ball in a crimped housing) that allows trapped air to bleed through to the radiator when the thermostat is closed.
A failed thermostat (stuck open) causes the engine to run too cool, resulting in poor fuel economy, high emissions, and poor cabin heat. If the thermostat sticks closed, engine overheating may result, the coolant may boil, and possible damage may result. Finally, a delayed thermostat opening may cause sudden temperature spikes and erratic temperature gauge behavior.
The cooling system is one of the most overlooked parts of an automobile (until it fails). Because modern vehicle cooling systems are complex, following the manufacturer’s recommendations is advisable to maximize the system’s efficiency, longevity, and performance.
