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Antifreeze: Red or Green?

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Antifreeze: Red or Green?

   There has been a very lively discussion going on about "Red" or Dexcool® antifreeze and regular "Green" antifreeze. I have been asked to explain the difference between Dexcool® and clear up some myths and misconceptions about both. This is quite a challenge because every company's antifreezes have different combinations of additives and inhibitors. I won't go into brand specific formulations but rather stick to the basic properties common to all antifreezes.

   One myth is that all red antifreezes are Dexcool®. There are standard antifreezes that are red and cars that have Dexcool® will be labeled as such. Another myth is that Dexcool® is not glycol based. Not true, all antifreezes are glycol based, including Dexcool®. Both ethylene glycol (EG) and propylene glycol (PG) are used as the antifreeze base. From here the additional additives and inhibitors are added. Each glycol has supporters, although the best choice depends on the intended use. There are several considerations to be made when choosing an antifreeze, the most important being performance. In the area of performance there is very little difference in EG and PG. Additives determine most performance criteria so all coolants supplied by a respectable manufacturer will perform well. The one major difference in EG and PG is toxicity.

   Because the most persuasive reason to use PG instead of EG based antifreeze is toxicity, we should discuss a little about toxicity. The first thing to think about is the difference between acute and chronic toxicity. Acute toxicity refers to toxicity that has a short duration. If you survive poisoning with an acute toxin, there are usually no lasting effects. Chronic toxicity on the other hand is something that lasts a long time. When poisoned with a chronic toxin, symptoms may not appear for a long time and they may last indefinitely.

   PG differs from EG in both acute and chronic toxicity's. In antifreeze we are most concerned about one time accidental ingestion. Therefore our interest is in acute toxicity. The acute toxicity of PG, especially in humans, is substantially lower than that of EG. Propylene glycol, like alcohol, is not toxic at low levels. In applications where ingestion is a possibility, PG based antifreeze is a prudent choice. EG is the most common base used in the manufacturing of antifreeze.

   Another consideration is that all antifreezes pick up heavy metal contamination during service. When contaminated (particularly with lead) any used antifreeze can be considered hazardous. Because of metal contamination many people feel that the toxicity of used antifreeze is the same regardless of glycol. This is where we look at chronic toxicity. PG is not a chronic toxin. EG and heavy metals are chronic toxins. Heavy metals, on the other hand are not acute toxins at the levels found in used antifreeze. For this reason PG based antifreezes, are much safer for people and pets in case of accidental ingestion even after use.

   In many US and Japanese antifreeze formulas phosphate is added as a corrosion inhibitor. European vehicle manufacturers, however, recommend against the use of phosphate containing antifreeze. The following will examine the different positions on this issue to help judge the pros and cons on phosphate inhibitors.

   In the US market, a phosphate inhibitor is included in many formulas to provide several important functions that help reduce automotive cooling system damage. The benefits provided by the phosphate include:

  • Protect aluminum engine components by reducing cavitation corrosion during high speed driving.
  • Provide for corrosion protection to ferrous metals.
  • Act as a buffer to keep the antifreeze mixture alkaline. This prevents acid build-up that will damage or destroy metal engine parts.

   European manufacturers feel that these benefits are achievable with inhibitors other than phosphate. Their main concerns with phosphate containing products are the potential for solids dropout when mixed with hard water. Solids can collect on cooling system walls forming what is known as scale. This concern comes from the fact that European water is much harder than water in the US. Because phosphate "softens" water by forming solids of calcium or magnesium salts that can dropout of solution, there is potential for cooling system blockage. The phosphate level in most US and Japanese antifreeze formulas do not generate significant solids. Furthermore modern antifreeze formulations are designed to minimize the formation of scale. The small amount of solids formed presents no problem for cooling systems or to water pump seals.

   Copyright © 2001 - 2003 Vincent T. Ciulla All Rights Reserved

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