Coolants for Diesel Engines

One of the most asked questions by RV owners is "What kind of anti-freeze must I use in my engine?" In the automotive world this is a fairly easy question to answer. If it's an older vehicle use the "green stuff" and if it's newer, use the "pink stuff". Except diesel engines have greater cooling requirements than gasoline engines so we need to better understand what these needs are and what types of coolants exist.

The original green stuff is Ethylene Glycol anti-freeze, the stuff that's been used for years. Mixing it 50/50 with water will give freeze protection down to -42� and will raise the boiling point to 265� F. Additives will be found in these coolants to inhibit corrosion and lubricate water pump shafts and seals. While the coolant will generally retain it's freeze protection and raised boiling point, these additives will eventually wear out. When this happens, excessive wear on the water pump will occur, you'll see more mineral deposits clogging the radiator core, and corrosion will speed up. For this reason it's recommended to change your coolant every other year under normal driving conditions. Because Ethylene Glycol is highly toxic, a trend has been to use Propylene Glycol in it's place. PG is less toxic if ingested but it's coolant protection will be identical to EG. As a rule PG coolant isn't widely used because it costs more and the only benefit is that it isn't toxic, like EG coolant.

The pink stuff was introduced by GM in the late 90s and called Dexcool. This was a "maintenance free" coolant purported to have a 5 year lifetime. It was quickly adopted by other manufacturers and is widely available - know as ELC, or Extended Life Coolant.

So, what's the difference? The majority of modern coolants is identical, whether the traditional coolant or the Extended Life Coolant (ELC). The boiling and freeze points will remain identical in either. The biggest difference is found in the corrosion inhibitor additives. These additives are a small percentage of the coolant but they play a crucial role in maintaining your cooling system. Traditional coolant uses non-organic corrosion inhibitors, such as silicates, phosphates, and borates. The ELC coolant removes these and replaces them with organic salts. These inhibitors have a greater life span than the traditional inhibitors. That's why the 2 year life expectancy jumps up to 5 years with ELC coolants. Even though the coolants themselves are compatible, the additives are not. Because the chemistry is so different, it's not advisable to mix the two coolants. The additives will not get along all that well and your corrosion protection will suffer. It's best to flush the old coolant out before replacing with the new ELC. In an emergency, coolants can be mixed but be sure to have the system properly serviced when time permits. Some manufacturers have specific requirements so not all ELC coolants are universally accepted by every manufacturer. It's best to look for the "Global" ELC coolants because they will be more compatible across vehicle brands.

What about diesel engines? Heavy duty engines, such as diesel engines, require a heavy duty version of coolant. There are three basic types of coolants - automotive, heavy duty, and universal. The biggest difference between automotive and heavy duty coolants is how much aluminum corrosion protection they provide. This is controlled by adding silicates to automotive coolants while a coolant designed for heavy duty applications is low-silicate. A universal coolant will contain enough silicate for automotive use but keep it low enough to allow it to be used in heavy duty applications as well. However, if a low silicate coolant is used in heavy duty applications, Supplemental Coolant Additives (SCAs) need to be added to the mix to provide adequate protection. This is especially important to reduce cavitation in diesel engines.

Cavitation is an important consideration in diesel engines. In order to improve heat transfer, many diesel engines use wet sleeve cylinder liners. This means that the coolant directly contacts the outside of the cylinder liner. These liners tend to vibrate under heavy duty operation. This vibration creates air bubbles that implode against the outer surface of the liner. This process is called cavitation and these bubbles can cause pitting and pin holing that can destroy the cylinder liner. That's why heavy duty coolants require a special nitrite inhibitors, defoamers, and buffers. These additives can be found in a separate container or they may be incorporated into the coolant, in which case it is known as Pre-formulated coolants. The SCA also help to reduce scale deposits in the system and aid in cooling improving heat transfer from the metal parts of the engine.

Check your SCA levels every 6 months or 25,000 miles (whichever comes first) to ensure that they are within tolerance. SCA test strips are available from Fleetguard filters, Freightliner dealers, or any other source of truck service or filer sales. If you are not using pre-formulated coolant then you will have to add the proper amount of SCAs at the initial fill. However, these SCAs will deplete over time and you will need to replenish them. If you have a coolant filter, it will be precharged with SCAs. The filter will help to maintain these levels but it won't bring up a "flat" system without getting an initial dose at fill up time. Regardless of the method of SCA distribution, pre-formulated, manually added, or SCA filter added, they will eventually wear out over time. Once they are gone you will suffer cylinder liner pitting, scaling, and corrosion.

Pre-formulated Coolant is a great aid to maintaining your cooling system. Two of the most popular coolants are Fleet Charge and various products by Fleetguard, which meet all of the requirements of diesel engine manufacturers. Fleet Charge and the Fleetguard coolants are pre-formulated coolants. It's an Ethylene Glycol based ELC coolant that is a universal coolant and will work in any application. It's SCA additives are reduced variability. In other words the SCAs won't wear out as fast as a non formulated coolant. If you need to add more coolant it is important to use more preformulated coolant in order to maintain the proper levels of SCAs. Either way, you will want to check those SCA levels on a regular basis. You can get them either pre-mixed, with deionized water or as pure coolant which you will need to mix with distilled water.

Proper maintenance of your cooling system's coolant will yield big benefits toward keeping your engine running nice and cool. Regular checking of SCA levels is an important point. Keeping your antifreeze to water ratio at 50/50 will result in the best balance between freeze protection and additive retention. Plus, using distilled water will reduce the amount of mineral in your cooling system. While tap water can be used, it varies greatly in mineral content and that's where a large part of your corrosion and blockage comes from. Also, if you use water that is highly softened, the salt will do a number on your coolant's additives. Stick with distilled water and you'll have less trouble later.

Addendum of 11/20/06:

Spartan chassis are being shipped with Final Charge Pre-formulated Coolant. Final Charge is a heavy duty coolant that works in any heavy duty engine. The biggest difference between Final Charge and other pre-formulated coolants is that Final Charge uses organic acid technology (OAT) to derive it's protection. This means that there are no phosphates, borates, nitrates, or silicates in Final Charge. You DO NOT add any SCAs nor do you have to check your SCA levels every 6 months. The coolant is designed for 600,000 miles or 6 years before it needs replacing but you do have to add a Final Charge Extender at 300,00 miles or 3 years. Final charge does not require coolant filters, inhibitors, or SCA additives not does it require monitoring. This appears to be the ideal coolant for an RV. If you have a recent Spartan chassis you should see a decal by the coolant surge tank advising that your unit is filled with Final Charge and warning you to not add any SCAs to the system. Final Charge is approved for Cat, Cummins, MB, or any other diesel engine. If you have trouble finding Final Charge you can also use Fleetguard's OAT coolant, which is compatible with Final Charge. That coolant is Fleetguard's ES Compleat OAT, which was formerly called Optimax. It is identical to Final Charge in that it lasts for 600,000 miles as long as the extender is added at 300,000 miles or 3 years. Generally ES Compleat OAT is more readily available at truck service centers.

Submitted by Mark Quasius - 2/21/06
 

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