Keeping your engine cool

by Bob Brady

Many readers, especially those that live in colder climes, have been asking me how often you should check your antifreeze, how often you should flush the cooling system, and whether or not one antifreeze is better than another.

Since you asked, here is the first installment of a two-part look at keeping your cool.

Antifreeze protects the cooling system from freezing in the winter and boiling over in the summer, since it contains inhibitors that also prevent both rust and corrossion in radiators and water pumps.

There are a wide variety of antifreeze brands on the market, with a number of these being from one supplier and simply packaged in different color containers.

Prices can and do vary based upon the specific brand and type of product that you choose to buy.

Keep in mind, too that antifreeze should be used even in a warm climate, since it contains additives that aid in the heat transfer process as well as provide metal corrosion protection.

Fleets estimate that 40 per cent of engine downtime is related to poor cooling-system maintenance.

Adding new antifreeze every two to three years without appropriate checks every two to three months means cooling system problems may go undetected.

Failure to regularly check coolant chemistry results in pitted cylinder liners, leaking water pumps, as well as radiator and hose damage.

A heavy-duty diesel engine generates enough heat to warm a seven-room house. To obtain ideal thermal efficiency (miles/gallon or km/litre) and to extend the life of cooling-systems, engines, and components, certain things are needed.

Thermostats, thermatic fans and aftercoolers are required to maintain the coolant’s temperature at an ideal operating level, regardless of outside temperature, speed and load.

In today’s engines, we can identify engine coolants as being either a “conventional,” or a “fully formulated” antifreeze system.

The major diesel engine original equipment manufacturers (OEM) recommend using what is known as a “fully formulated”, or premixed, coolant, offering a total cooling-system package.

Conventional coolant consists of an ethylene-glycol antifreeze that contains a corrosion inhibitor consisting of chemicals such as silicate, phosphate, nitrate, and azoles.

Let’s look at the characteristics of these four inhibitors.

Silicate is the primary conventional inhibitor for aluminum. Heavy-duty truck and equipment coolants ideally contain less than 250 parts-per-million (ppm) silicate concentrations.

Phosphate is an inexpensive ph buffer (ph is a chemical symbol denoting the measure of the alkalinity of the coolant) and is used only in some antifreeze brands. This is an important point; Detroit Diesel, MTU, Mercedes-Benz, BMW and Volkswagen are some manufacturers that do not permit the use of phosphate in their cooling systems.

Nitrate, the next ingredient, is a corrosion inhibitor that protects soldering and aluminum parts.

Next, azoles provide copper and brass protection. The two most widely used azoles are mercaptobenzothiazole (MBT) and tolyltriazole (TT or TTZ).

A “fully-formulated” antifreeze or coolant is a product that contains all of the necessary inhibitors for both diesel- and gasoline-powered engines. In addition, it complies to the American Trucking Association’s Maintenance Council recommended-practice specification 329 or 330 – known in the industry as TMC RP-329 or 330 (the recommendations are published in its bulletin).

Note that today there are two major antifreezes: EG and PG. The main ingredient in most standard antifreezes is ethylene glycol (EG), while the second is propylene glycol (PG). Both EG and PG are manufactured from carbon, oxygen and hydrogen.

PG is less toxic than EG, but is more expensive; nevertheless, there is a major move to adopting PG for truck fleets because of its additional advantages.

Conventional coolant contains an average mixture of 50 per cent EG and 50 per cent water, although different mixture ratios can be used based on the ambient operating temperatures that the engine operates under.

Typically, antifreeze manufacturers suggest using no less than 40 per cent antifreeze and no greater than 67 per cent deionized water. Concentrations greater than 67 per cent of EG are counterproductive and are not recommended.

PG coolants provide maximum protection at 100 per cent A/F content. Some PG antifreeze mixtures can contain some water, but non-aqueous PG, or NPG, contains no water at all.

Typically, EG and water at a 50/50 mixture will provide a freeze protection level of -27F/-33C, and boil-over protection to 260F/127C with a 15 psi radiator pressure cap.

The boiling point of NPG is 369F/187C at zero psi (no radiator pressure cap).

In addition, the freezing point for NPG is -70F, versus -38F for EG. Most engines will overheat using EG at approximately 250F/121C when using a 13 psi cap, whereas NPG can tolerate temperatures above 350F/177C.

It is extremely important that engine coolant be properly maintained to avoid scale deposits, corrosion, cavitation-erosion and possible accumulations of silicate drop-out, which forms green goo.

Let’s look at each one of these conditions.

Scale Deposits: hard water is classified as any water that contains over 100 ppm of calcium and/or magnesium. Scale buildup can block a cooling system’s ability to transfer heat efficiently, resulting in engine overheating. As little as 1/16″ (1.5 mm) of buildup will reduce heat transfer by 40 per cent.

In a hot engine’s cooling system, the hard calcium and magnesium salts in the coolant become less soluble, and get deposited on cooler metal surfaces and areas where flow is low or turbulent. Trapped air, bubbling around a heat source, increases the tendency for scaling in these areas.

An increase in pH, or alkalinity, will also increase the potential for scale deposits.

Overheating due to scaling can result in cracked or warped cylinder heads and blocks or higher running temperatures for coolant and oil. As well, a thermatic cooling fan could malfunction since its sensor can get coated and fail to engage until an elevated temperature is reached.

Corrosion: metals corrode as they follow their natural tendency to revert to their primary ore condition.

In the presence of water, cast iron will form a reddish-brown oxide – rust.

Other metals, due to corrosion, will form a specific color.

The degree of metal corrosion is affected by a coolant’s pH level and concentration of dissolved oxygen and carbon dioxide, the corrosion inhibitors present in its additives, as well as its operating temperature. Other factors include acids formed in the combustion of the fuel, engine-surface deposits and metal stress.

A coolant’s pH level is gauged on a scale of between 0 and 14. The closer to zero, the more acidic the coolant, while the closer the value towards 14, the greater the coolant’s level of alkalinity.

Typical pH values are maintained with a coolant additive package containing a pH buffer – the ideal value is between 8.5 and 11.

Permitting the pH value to drop below 8.5 causes both cast iron and steel components, as well as aluminum, copper and brass, to corrode at a faster rate.

Allowing the pH value to exceed 11 promotes aggressive corrosion of both aluminum and solder within the engine and radiator.

A common pH buffer additive consists of borate, which is found in premium antifreezes.

We’ll explore more of these problems next month. n

– Bob Brady is the president of Hitech Consulting in Burnaby, B.C.

Have your say

This is a moderated forum. Comments will no longer be published unless they are accompanied by a first and last name and a verifiable email address. (Today's Trucking will not publish or share the email address.) Profane language and content deemed to be libelous, racist, or threatening in nature will not be published under any circumstances.