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What You Need to Know About Diesel Antifreeze and Coolants

Originally Published in MotorHome Magazine

If you own a diesel motorhome, there are a few things you need to know about the coolant/antifreeze circulating in your engine block.

During the past few years, taking care of your automobile’s radiator and coolant has become a lot easier thanks to the new long-life coolants on the market. Many of these products last up to five years or 150,000 miles in an automobile. A diesel motorhome is a different situation, so the coolant system care practices for your car are not transferable to your coach. Depending on which engine is in your motorhome and the specific type of coolant it uses, your maintenance requirements may be greater, or even fewer, than those for your automobile.

The main purpose of coolant/antifreeze in a typical automobile engine is generally well-known. In the summer it raises the boiling point compared to plain water and in the winter it prevents the engine from freezing. It also carries heat away from critical engine components and dissipates it through the cooling system into the surrounding air. In a diesel engine it also serves as a carrier for other additives such as corrosion inhibitors and anti-foaming agents, and provides protection against cavitation and cylinder pitting.

Diesel motorhome engines fall into one of two categories when it comes to the engine block and the resulting type of coolant it requires. Smaller diesel engines such as the Cummins ISB and the Cat C7 are examples of dry-sleeve engines, which are more like typical automobile engines. Due to their design, these engines are not typically susceptible to cylinder wall cavitation, so they are not addressed in this article.

The larger diesel engines such as the Cummins ISC, ISM, ISL and ISX as well as the Cat C9, C11 and C13 all use wet-sleeve designs. These wet-cylinder engines allow the sleeve (that contains the piston) to come in direct contact with the coolant. Wet sleeves allow the engine to transfer more heat than dry systems, but because the iron sleeve is in direct contact with the coolant, they have some special requirements for their coolant/antifreeze.

Wet-cylinder diesel engines transfer a lot of vibration and movement from the pistons to the cylinder walls that can create coolant cavitation (tiny bubbles) behind the cylinder walls. Cavitation can ultimately lead to pitting of the cylinder walls from the outside in. Heavy-duty coolants formulated for diesel engines contain additives that deal with these tiny bubbles. Without getting too technical, it’s pretty clear that the coolant is important in these expensive diesel engines.

Your diesel engine can be filled with a variety of coolants, depending on the choice of the chassis manufacturer. For our purposes we can divide coolants into two major categories. The first type is heavy-duty, fully formulated products that require regular testing and adjustments. The other common type is known as long life/extended life coolants (LLC/ELC). If you are unsure what you have or you don’t find it in your owner’s manual, contact your chassis manufacturer for more information.
In order to find out what coolants are commonly used today in new motorhomes we spoke to three major chassis manufacturers. When a chassis manufacturer purchases an engine from companies such as Cummins, Caterpillar or Navistar, the engines are delivered without coolant and the chassis manufacturer chooses and installs the coolant. Each engine manufacturer does, however, publish its own specifications, such as Cat’s EC-1, Navistar B1 or Cummins 14603. The owner’s manual for your engine will give you more details on the exact specifications required for your diesel engine.

Currently, Freightliner delivers its chassis to the various motor­home manufacturers with a product known as Fleet Charge (also sold under the Alliance brand name), which is a fully formulated coolant that requires testing every six months. Spartan, on the other hand, uses Final Charge, an ELC coolant that does not require testing. A spokesman for Spartan said that it has used this product for several years because of the reduced maintenance requirements to owners. We also talked to Roadmaster, manufacturer of chassis for Monaco and Holiday Rambler, and it indicated that it  also plans to use ELC coolants as it transitions to its new Navistar MaxxForce line of diesel engines, which will also include the Workhorse line of chassis.

The main advantage of these LLC/ELC coolants is that they have a service life of many years (some manufacturers claim up to 600,000 miles), and they don’t require testing. Examples of LLC/ELC coolants are Old World’s Final Charge, Cat ELC, Fleetguard ES Compleat OAT, Zerex Extreme Extended Life and Shell Rotella Ultra ELC. If your coach uses these coolants, the main requirement is to ensure that the system is properly filled, and at approximately three-year intervals, most of them require an extender to be added to restore the additive package. If you ever need to add makeup coolant, it is important to not only add the right type but also to add it at the proper dilution. Some products are sold pre-diluted while others need to be mixed 50 percent/50 percent with distilled water in order to ensure the proper antifreeze properties are maintained.

If your motorhome uses a conventional coolant (also known as a heavy-duty or fully formulated coolant), one of the drawbacks is it requires testing and additive supplementing. Freightliner suggests testing every six months. Additives need to be tested because they are sacrificial in nature and are being used up during the operation of the engine. Testing is one of those tasks that’s easy to overlook and often difficult to accurately conduct. Typically it involves a trip to the local service center, but you can also buy test strips, and assuming you use them properly and don’t let them expire (yes, they have a shelf life), you can check your coolant’s condition.

There are two types of test strips and additives, so you have to use the correct test strip depending on which additives your coach is using. Alliance/Fleet Charge and Detroit Diesel Powercool use nitrates. A two-way test strip should be used when testing these coolants. There are three-way test strips that measure freeze point, molybdates and nitrates. If you use the wrong test strip it could result in incorrect results and improper dosing.

If you test your coach’s additive levels and find them to be out of spec, you will need to restore them with the addition of a product such as Fleetguard DCA2 (DCA4 includes molybdates), Penray Pencool or others. Again, it is important to determine what products meet your engine and coolant manufacturer’s specifications. Additives can be purchased at most large chassis service centers as well as truck stops.

If you have been enjoying your motorhome for years and have not given a second thought to your engine’s coolant, you may want to check with your chassis or engine manufacturer and find out what type of coolant your engine came with from the factory. If you have been getting your chassis serviced at regular intervals there is a good chance the coolant has been checked and supplemented as needed.

If you have an engine that is pre-filled with a coolant that requires monitoring and you want to eliminate one more complication in your life, one solution is to convert it over to an ELC coolant. Depending on your situation this may involve a complete coolant system drain and flush, which can be expensive, but it eliminates the need for future testing. There are also conversion chemicals available such as Final Charge Converter that you may be able to use. This is a very important procedure and one that’s best left to the experts at your local chassis service center.

Our intention in this article is not to cover every aspect of coolants and turn this into a chemistry lesson, but rather to make you aware of testing and the fact that there are options available, if you don’t want to be bothered with monitoring and testing additives.

Not only do they require less maintenance, but many ELCs also offer better heat transfer when compared with typical coolants. ELC coolants also offer the benefit of longer water pump and seal life because they don’t contain abrasive silicates. Some older engines, however, may not be compatible with ELC coolants because of gasket or seal incompatibility. It is critical that you check with your engine manufacturer to ensure you are making the right choice.

Although testing and maintaining additive levels is not the worst thing in the life of a motorhome owner, why bother with it if you don’t have to? After doing research for this article, I have decided to convert to an ELC coolant for my personal coach.

Final Charge meets all the specifications of my Cummins ISC engine, and should last many years with little to no service requirements. I’ll also use the same product in the diesel generator to prevent having to carry two products. If you don’t mind twice-a-year testing and additive supplementing, fully formulated/heavy-duty coolants will also serve your engine well as they do many long-haul trucks on the road today.

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