Keep the ‘cool’ in cooling systems

April 1, 2014
Changes in technology for the “David and Goliath” extremes of engines used in both hybrid passenger cars and light-duty diesel trucks definitely will ruin your day if you don’t know how they operate. 

A major cause of a brown-looking rust in a DEX-COOL® vehicle’s cooling system also can be the reaction of the coolant and casting sand left over from the manufacturing process. 

Changes in technology for the “David and Goliath” extremes of engines used in both hybrid passenger cars and light-duty diesel trucks definitely will ruin your day if you don’t know how they operate. Assuming all coolants are created equal can ruin your day as well. But the encouraging news is there’s good money to be made in cooling system repairs.

While oil change and spark plug replacement intervals have gone up over the years, surveys indicate 35 percent of vehicles inspections reveal an improper coolant level, improper coolant mixture or coolant leaks. All of this gives you the green light to sell proper cooling system maintenance and repairs to your customers.

Coolant basics

The center focus on cooling systems always has been the coolant itself. Do you have enough coolant in the system? Are there leaks? What is the freeze protection? Is the coolant in good condition? Those used to be about the only questions regarding coolant, but times have changed.

Generally speaking, ethylene glycol has around 3 percent additives present to prevent corrosion, control pH levels and add color to the coolant. Added to the coolant is, of course, water, which averages around 50 percent of the coolant mix.

Most of us have seen the charts giving a clear picture of the ratio of the concentration of antifreeze vs. water in coolant. As antifreeze concentration goes up, the temperature protection goes up with it until that concentration goes past the 70 percent mark, where the freeze protection is actually reduced.

With the engine off, connect the negative meter lead to the negative post of the battery. Submerge the positive meter lead in the coolant, touching only the coolant and not any metal in the radiator. First test with the engine off, then start the engine and observe while cranking and with the engine running. Image courtesy of MACS Worldwide

Testing has been simple, with a hydrometer that checks the specific gravity (and freeze point) of coolant. Hydrometers are cheap — some even fit in your pocket. But cheap can sometimes be expensive. Laboratory studies indicate that hydrometers can be as much as 23 degrees Fahrenheit off in their measurements for freeze protection.

In recent years, the refractometer has become more popular because it’s more accurate (within 1 degree Fahrenheit) and dependable for testing coolant strength to ensure ample freeze protection. They are also compatible for testing both ethylene glycol (EG) and propylene glycol (PG), while the hydrometer measures either one or the other.

EG vs. PG

Speaking of propylene glycol, did you know no OEM vehicle manufacturer recommends it? That is why you will see it only in the aftermarket. It’s more expensive, too, so why has it ever sold?

Unlike EG, PG is biodegradable — and safer for pets regarding accidental poisoning. This benefit is not because it is less toxic, but rather, it is less sweet to the taste. If your dog or cat doesn’t like it, they are less inclined to drink it.

PG is sold by Peak under the brand name Sierra, and by AMSOIL. EG is required in more than a dozen states to contain a bittering agent called dentonium benzoate to prevent accidental pet poisoning.

Leaking systems

There is a radiator air bleed with an access hole hidden by a plastic radiator support beauty cover. A factory tech tip on this car is to use your scan tool to turn on the auxiliary coolant pump that supplements the belt driver water pump with engine coolant circulation duties as a way of helping burp air out of the system during refills. 

When a cooling system leaks, air replaces the leaked out coolant. The reaction between DEX-COOL and air creates a rusty brown substance that clogs up various components and passages in the system. Regarding air intrusions, keep in mind coolant leaks aren’t always onto the ground or into the combustion chamber via a bad head gasket. Radiator caps have two seals. One seals and allows the radiator to expel high temperature/high-pressure coolant into the reservoir. The other allows vacuum created by a radiator that is cooling back down to pull coolant back from the reservoir.

If the reservoir is empty, the hose between it and the radiator is not sealed or the cap is bad, air entering into the radiator can be the result. Caps are cheap-enough and easy-enough fixes. Test and replace — or just replace.

On the subject of head gaskets, leaks are not always easy to find with a compression gauge or cylinder leak tester. Using a combustion leak detector in the coolant works well, and can be tested by moving it to the exhaust pipe while the engine is running. Another valuable tech tip is to remove the radiator cap (engine cold) while performing a cylinder leak down test on each cylinder at TDC compression. If you see the coolant level begin to rise in the radiator, there is a leak near that cylinder in the head or head gasket.

Electrolysis

When coolant is neglected, the chemical reactions can cause some interesting side effects. Besides rust and corrosion creating havoc on metals, hoses, plastics and gaskets, electrolysis can occur. There are two types of electrolysis:

• Type A is not caused by bad coolant, but rather bad electrical connections and grounds. Current for various electrical accessories on the vehicle takes a path through the coolant.

• Type B occurs because the acidic nature of the coolant and dissimilar metals in the cooling system create a makeshift galvanic battery in the cooling system.

The system in place has a complicated set of pumps, electric valves, hoses, sensors and, of course, the metal (thermos) heat storage tank. 

Diagnosing electrolysis is easy. Using your DVOM, simply set your meter to DC volts and measure the voltage in the actual coolant. A voltage reading greater than 0.3 volt will accelerate the deterioration of an aluminum radiator or heater core. Check all ground circuits under the hood.

If you still haven’t resolved the voltage problem, remove one fuse at a time until voltage drops, and verify that specific circuit. Type B electrolysis will produce a more acidic nature within the coolant, so in addition to the voltage test, use inexpensive pH strips to test the pH level of the coolant. Generally, any pH level below seven is considered acidic.

Regardless of whether the electrolysis is Type A or B, the coolant must be flushed and replaced — thanks to the aluminum corrosion inhibitors being destroyed.

Corrosion

Corrosion is a form of rust that produces aluminum oxide. It appears in the form of a white powder-like coating, accompanied by metal surfaces of the cooling system literally being eaten away. The classic example would be aluminum gooseneck thermostat housings, to where the upper radiator seals.

Besides creating leaks in some situations, the aluminum oxide/corrosion reduces the heat transfer ability of the coolant to get rid of heat in the engine. This is because it provides an insulation effect on the metals it covers.

Cavitation

The belt-driven pump is one of the few weak links on the Gen II Prius. The pump’s bearing tends to go out around 120,000 miles — and as it does so, it allows the bearing seal to leak and sometimes chew up the drive belt. 

Cavitation is the sudden formation and collapse of low-pressure bubbles. With gasoline engines, the pressure drop can occur at the inlet of the water pump. These bubbles produce a pitting of the solid metal. Occasionally, a manufacturer will release a redesigned water pump via a Technical Service Bulletin (TSB) to address cavitation issues that were not discovered during vehicle design and validation.

Filling the system

Approximately 15 percent to 20 percent of the coolant in the system stays in the system. If the radiator cap and overflow hoses are sealing good, the overflow reservoir should empty during a radiator drain plug pull. But you’ll still have some coolant in the block, even if the block drains are pulled.

If you don’t purchase pre-mix, be sure to avoid using tap water. Some vehicles will even have a “No Tap Water” sticker under the hood. Tap water will vary from community to community and, of course, well water is rich in trouble-inducing minerals. Distilled water contains fewer minerals, so make sure you keep it in your shop in ample supply.

Gen III Prius also does away with the heat storage tank, but attacks early engine start HC production with a special HC absorber chamber in the catalytic converter; it is physically actuated via warm coolant routed to an actuator on the side of the cat.

Because of cavitation issues, you want all the air out of a system. That can be done several ways, with some more effective than others. The obvious air bleed screws and following the manufacturer’s procedures are in order, but there are a couple of effective generic methods out there for a successful air-free fill:

• The funnel system uses radiator filler neck adapters, which allow a special funnel with a shut-off valve to be fastened to the radiator or pressurized degas/reservoir tank fill neck. You fill the radiator via the large funnel with coolant, then start the engine. This allows a thermal cycle to cause some expansion of the coolant in the radiator. The coolant expands into the large-volume funnel and as it does, air bubbles in the system come to the surface of the coolant in the funnel.

Remember, coolant can take away heat from a water-cooled engine, but air pockets can’t. Air pockets can’t provide sufficient heat to the passengers via the heater core, nor can they give an Engine Coolant Temperature (ECT) sensor an accurate reading. Air pockets can even give a false diagnosis for a faulty head gasket.

• The alternative to the refill funnel is an air lift system. Using shop air to create a venturi-created vacuum, these inexpensive tools are excellent at getting an air-free fill. Like an A/C vacuum pump, remove the supply of vacuum (pull off the shop air) and look to see whether the vacuum decays. If it doesn’t, large leaks are not likely.

Now with a fill hose primed with coolant, twist the valve on the air lift unit to allow the primed hose — sticking down into a container of coolant — to pull the coolant into the system. The whole process takes only seconds.

David and Goliath Engines

GM’s Chevrolet Volt extended range EV (a hybrid of sorts also) requires a special premix DEX-COOL® containing deionized water (nonconductive) for that vehicle. 

Middle-of-the-road engines have had a few innovations in cooling and heating systems in recent years, such as electric auxiliary water pumps to move coolant into the heater core for better cold temperature/idle heater performance. But there is nothing newer and more complicated than the cooling systems on Toyota Prius and Ford Powerstroke diesels. When you raise the hood on either of these vehicles, you might feel a bit intimidated unless you’ve had some training and experience.

Toyota Prius Cooling

The Prius was a single-mission vehicle: It’s always been a hybrid electric vehicle and nothing else. Part of that hybrid mission is superior fuel economy, and the other part is getting that Advanced Technology Partial Zero Emission Vehicle (AT-PZEV) rating. One feature which helps to achieve the AT-PZEV is a special cooling system that lowers hydrocarbon (HC) emissions during cold starts.

Generation II Prius vehicles (2004-2009) do so by sending hot coolant from an air/vacuum insulated hot coolant (thermos) storage tank into the cylinder head. Mounted in the left front inner fender, this tank — quite often damaged in minor frontal collisions — can keep coolant at operating temperatures for more than 24 hours. That’s a good thing to know when you are draining it (the heat storage tank is the lowest point in the cooling system) and not expecting to be burned by hot coolant after the car has sat overnight at your shop.

Keep in mind on this generation of Prius, the bottom quarter of the radiator is separate from the top and used for coolant to cool the inverter, converter and transmission mounted motor/generators, so the radiator petcock will be about 4 inches from the bottom of the radiator. When the gas engine is in idle stop mode, the auxiliary water pump keeps the heater core filled with hot coolant on those cold winter mornings.

In addition to the belt-driven pump and auxiliary electric water pump, there is another electric pump for engine coolant just for this early-start HC emission reduction feature. It runs to regularly keep the heat storage tank with hot coolant — and, of course, to pump the hot coolant to the engine on cold starts. You always should hear that pump run for a couple of seconds whenever you switch off the main power button.

A fourth pump (three electric and one mechanical) is under the hood. It is solely there to move coolant in a totally separate cooling system that keeps the high-voltage electronics cool. Even though that system is separate from the gas engine’s system, they both use the same Toyota coolant. Make sure you use that coolant, too. When cooling electronics that have hundreds of volts and amps, you don’t want to take chances on creating corrosion.

Also on the Prius, make sure you know which pump is where, and that you are able to describe what you want to your parts person when ordering a “water pump.” Generation III Prius (2010 and newer) did away with the weak link mechanical water pump in lieu of a12-volt electric model, which negated the need for an auxiliary engine coolant pump. Gen III Prius also does away with the heat storage tank, but attacks early engine start HC production with a special HC absorber chamber in the catalytic converter — it is physically actuated via warm coolant routed to an actuator on the side of the cat.

Ford Powerstroke Cooling

Both the primary and secondary cooling systems on Ford’s 6.7L Powerstroke also cool the dual EGR coolers, as shown here in this cutaway.

Those who work on these on a regular basis appreciate all the complexities and service “opportunities” this engine provides, especially the 6.0 models. Ford uses engine oil that is greatly pressurized to operate its fuel injectors. As with all diesels that make tons of NOx emissions, an EGR valve is in place to cool the combustion chamber down during the power stroke. To make the EGR action more efficient, there are one or more EGR coolers that use engine coolant to cool the cooler(s) down.

Engine coolant also is used to cool the engine oil reservoir in place to manage the high-pressure oil system in place to assist with HP direct fuel injection. That’s asking the oil to do a lot, and the engine coolant to do even more.

One frequent failure item is the EGR cooler. When it leaks, you can get coolant in the exhaust (white smoke) or in the crankcase. Simply replacing the EGR cooler is often not the complete answer. Understanding the flow of air, oil and coolant on any diesel is very important.

In the case of Powerstrokes, the oil reservoir that supplies the oil assisting in HP fuel pressurization gets the engine coolant before the EGR gets it. When the oil is hot because of poor maintenance or the engine has been “chipped” to have more horsepower, the coolant will be hotter than normal before it hits the EGR cooler. By all means, replace the leaky EGR cooler — but also look into the other factors that made the coolant hot enough to begin with, such as the coolant passageways in the oil pump reservoir.

Casting sand has been a problem with these Ford diesels, as has air cavitation, but an even bigger problem has been the use of tap water and non-recommended coolants containing silicates. When serving the newer 6.7 Ford Powerstrokes, anyone servicing the cooling system will be in for a real shock. There are two complete cooling systems: one for the engine and heating the heater core; the other one for cooling the fuel conditioner and transmission cooler. Both systems have their own water pumps, radiators and dual thermostats, which are located in each radiator and on the engine.

The Prius and the Powerstoke truly are examples of where cooling systems have taken a quantum leap in complexity — and that means we’ll have to continue to keep up to date in order to keep our customers engines cool and heater cores warm.

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SIDEBAR: Coolant chemistry

Even within the ethylene glycol (EG) family of coolants, there are a fair amount of differences. The original green EG antifreeze many of us grew up with is now obsolete. Green in color, it went by the name Inorganic Additive Technology (IAT). It contained borates, phosphates and silicates, the last of which could drop out of the mix and become abrasive.

When cavitation occurred because of low levels in the systems and sharp bends in the cooling system were present, the velocity of the silicates in the coolant could, at times, cause rapid repeat component failures. It was not unheard of to see a new heater core begin leaking in just a few hours — as the abrasive nature of the silicates works as a sandblaster when the aforementioned conditions occurred.

When changed regularly, IAT has good corrosion protection, but the additives that afford this benefit are consumed when maintenance is neglected. IAT also can cause early failures of ceramic-phenolic seals commonly utilized in more modern water pumps.

Organic acid technology (OAT), made popular by GM’s DEX-COOL®, is the OEM coolant not only for GM, but also many Asian and European automakers. GM started with it in 1996 and deemed it a five-year/150,000-mile coolant. While OAT gives a properly maintained vehicle a long life coolant thanks to longer-lasting additives, the older IAT and the newer OAT should never be mixed for one simple reason: Add some green to a late-model vehicle, and that orange long-life coolant no longer has the long-life characteristic.

Chrysler, Ford, Mercedes and some others recommend not using OAT / DEX-COOL coolant in their late-model vehicles. For those vehicles, a hybrid organic acid technology (HOAT, a.k.a. G-05®) formula of EG is used. A visit to Zerex’s website (or a look at the back of a gallon jug) will give you the scoop on which coolant is for what, along with a simple color coding of green for the old EG IAT (conventional short-life antifreeze), orange for OAT (GM DEX-COOL), and yellow for the HOAT EG.

Those are strictly the colors for Zerex, though. HOAT can come in blue, pink, orange and blue — and even green on some Chrysler products. While HOAT EG does contain some silicates, the amount is less than its predecessor; the old conventional green IAT OAT / GM DEX-COOL had a very rough road in the first few years.

OAT / DEX-COOL contains ethylhexanoic acid (2-EH) as a corrosive inhibitor. 2-EH is prone to damaging plastics like the Nylon 66 used in intake manifold gaskets and radiators. G30 OAT and Peak Global OAT do not use 2-EH. Besides 2-EH found in some OAT / DEX-COOL coolants, air was determined to be a major factor in causing system breakdowns.

If those formulas weren’t enough, phosphated organic acid technology (POAT) came to market in 2008, for newer Mazda engines made for Ford. It’s a dark green color.

Which coolant do you use? Which coolant should you use? If you have a trusted coolant supplier supplying you with a universal coolant that has long life, works well with any other coolant and has served you well for years, I will refrain from arguing that you change a practice that works. On the other hand, if you get a vehicle with repeat cooling system component failures, measured electrolysis, or major contamination/breakdown of coolant, go find the proper OEM recommended factory coolant.

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