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Part II: SCA Tech Talk (more than
you ever wanted to know about coolant and its additives)
You learned in "Choosing and Using" that the important understanding of SCAs is: knowing that they exist, they are necessary in diesels, that you use them at 3% in new, low silicate coolant and that maintenance is best performed on a test-to-add basis. Now, here is the rest of the story!
Two dominant technologies:
In this corner, we have the Penray (Nalcool) technology. This family of products is provided to the aftermarket as Pencool 3000, Detroit Diesel PowerCool, GM Good Wrench SCA, Caterpillar diesel coolant additive, and others. In the other corner, we have Fleetguard DCA-4. This technology is used at Cummins Engine, Ford, and Navistar. Both are effective, certified ASTM compliant products. Chart 1 shows a comparison of the two.
The primary difference centers on two debates: cylinder liner cavitation protection and the choice of pH buffer. The Pencool position is that phosphate and silicate both have admitted solubility limits. By using borate instead of phosphate, Penray believes the overall stability of the coolant is improved, making it more tolerant to overdose. This is a strong argument because, let's face it, human mentality says, "If a little is good, more is better." This just isn't true with SCAs. Penray also differs with the proposal that molybdate improves the effectiveness of nitrite, permitting lower nitrite concentrations in the coolant without sacrificing liner protection. Therefore, Penray uses nitrite alone as its liner protection, recommending at least 1200-ppm concentration. Almost three decades of experience support that this system works extremely well.
Fleetguard-Nelson, a subsidiary of Cummins Engine Company, has developed several products. Their older products closely resemble Pencool, so we will discuss the different technology here. Fleetguard DCA-4 employs a traditional phosphate pH buffer, resulting in a stronger RA (Reserve Alkalinity) value than the borate alternative. The key to preventing problems rests in the extra chemical stabilizers formulated into the package by Fleetguard as well as education to prevent improper use and over dose situations. The DCA-4 package uses nitrite and molybdate together to prevent cylinder liner cavitation. Fleetguard supports the position that a synergy exists by publishing several SAE papers on the subject. Many loyal customers suggest that it works as well. The advantage of lower nitrite concentrations is that, in laboratory testing, solder corrosion increases measurably as nitrite concentration increases. Therefore, the argument is that if the technology of using two chemicals at a lower dose adequately protects the liners-while permitting lower nitrite concentrations-the life of a copper/brass radiator may be improved.
There are many imitators of the principle brands. Some fleet customers report that these other brands may omit some components to reduce cost. SCAs are pretty inexpensive to begin with, the top brands cost about $30 per truck per year to use, less if the fleet is using fully formulated antifreeze.
Our lab, working for problem-plagued fleet operators, has identified bargain brand SCAs that provide essentially only nitrite and pH buffer (probably because test strips can measure those components). Meanwhile, of course, the rest of the cooling system suffers. Both Penray and Fleetguard-Nelson now have practices in place that can eliminate scheduled coolant changes in heavy trucks. Both have published fleet experience data with mileages approaching 1,000,000 miles without changing the coolant. (Well, intentionally, at least, but leakage is another subject.)
SCA Recommendations for Selected Systems:
* Red-orange ("Strawberry Red" color extended service antifreeze is available as an option.
Maintenance recommendations for the extended service antifreeze vary by engine make:
Caterpillar: add extender at 300,000 miles, drain at 600,000. Do not mix with other types of coolant and other SCAs are not required.
Cummins: a silicate-containing SCA is required and normal maintenance with SCAs is recommended. Drain and replace at 240,000 miles.
Detroit Diesel: add extender at 150,000 miles, drain at 300,000. Do not mix with other types of coolant and other SCAs are not required. $$$