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FCP Euro Service Kits

FCP Euro Kits

Engine coolant - that ubiquitous (traditionally) green, sweet smelling, slick liquid present in virtually all automobiles can be considered one of the most important fluids in the engine. It serves many purposes -  one of which is to help remove heat from the engine. Not only is it one of the primary methods of cooling the engine - it also plays an important role in helping to prevent internal galvanic corrosion of components in a closed-loop system.

Engine coolant consists of a mix of ethylene glycol (or propylene glycol) , distilled water, a small splash of corrosion inhibitors/buffers, and dye.

Ethylene Glycol

Green CoolantEthylene glycol is used to lower the freezing point of the mixture (which prevents the coolant from freezing and damaging engines) and also to increase the boiling point. When the cooling system is sealed with a radiator cap, the combination of the sealed system and ethylene glycol both contribute to a significantly wider operating rage for the coolant. However, a 50/50 mixture of ethylene glycol and water only has about 3/4 of the heat capacity of pure water. In road-going passenger cars, this usually isn't a problem. One of the major drawbacks of using ethylene glycol is it's toxicity and sweet taste, which can attract children and domestic animals.

Propylene Glycol

Propylene glycol is a less-toxic alternative to ethylene glycol but also oxidizes with exposure to air into acidic byproducts which can be extremely corrosive. Additionally, propylene glycol's useful lifetime is significantly reduced by bacterial contamination - it has a tendency to form slimy growths which foul the cooling system and necessitate frequent flushing and cleaning. When bacterial growths proliferate in propylene glycol coolants, the pH of the coolant rapidly takes a nose-dive into the acidic zone. Propylene glycol based coolants often contain large amounts of pH buffers, which can neutralize acidic compounds to keep coolant in the neutral pH range. Additionally propylene glycol is significantly more expensive to produce - which has prevented the wide-spread use of propylene glycol based coolant.

Distilled water is used because it has all solubles removed. Dissolved content in water can precipitate out and form solids in the coolant, and can combine with coolant to form nasty byproducts. Dissolved salts form ions that can accelerate galvanic corrosion in coolant loops because of the dissimilar metals involved.

Freezing point chart Freezing point chart of ethylene glycol mixtures

The most common mixture of glycol to water is usually 50/50

The ratio of ethylene or propylene glycol to water determines the freezing and boiling point of the mixture and heat capacity of the coolant. More water will shrink the window in which the coolant stays a liquid, but can carry more heat per unit mass of coolant. Race teams often will run with no ethylene glycol or propylene glycol to maximize the cooling capacity of the cooling system, and because the slick and slippery glycol compounds pose a safety and clean-up hazard should an accident occur on the track. The most common recommended mixture of glycol compound to distilled water is usually 50/50. Increasing up to 65% ethylene glycol and 35% water can lower the freezing point and raise the boiling point, but past that ratio, more ethylene glycol will actually raise the freezing point again. In this particular case, more ethylene glycol to water is not better! Generally coolant is widely available as a pre-mixed and ready-to-use 50/50 solution as a convenience and fool-proof combination. It's also important to note that among engine coolants, ethylene glycol is not broken down or consumed over the operating life of the coolant. The "expendable" portions of coolant are the corrosion inhibitor additives and the pH buffers.

Jeep XJ Water Pump Cavitation and corrosion damage on a Jeep XJ water pump

Corrosion Inhibitors

The corrosion inhibitor pack is where the types of coolant diverge - the three major types of corrosion inhibitors and buffers determine the category in which the coolant falls into. Typically European car manufacturers will have a different package of additives than Japanese car manufacturers or American manufacturers. Even among regions, different years dictate different types of coolant, often even for the same  model car. Common among all of the additive packs is a small amount of pH buffering and lubricants and seal conditioners. The pH buffering is used to balance and control the acidity or alkalinity of the coolant when contaminants are introduced, and the lubricants and seal conditions help keep the water pump, rubber gaskets, and carbide seals in peak working condition. During the breakdown of the various types of corrosion inhibitors, I'll reference "fresh" or "exposed" metal - you might think the cooling loop inside your engine is a gentle meandering flow of coolant, but in reality cavitation along water jackets and water pumps produces extremely harsh conditions that consistently break down and expose fresh metal surfaces. This is the reason why you can find pictures of water pump assemblies with blades that look like they were broken apart by a sledgehammer. in extreme conditions, cavitation can cause micro-pitting of cylinder liners and water pump impellers, causing them to crack.

Subaru Long Life Coolant, which is a traditional IAT coolant. Subaru Long Life Coolant, a traditional IAT coolant

IAT - Inorganic Acid Technology

Inorganic Acid Technology is one of the earliest and most ubiquitous types of engine coolant. In American formulations, IAT coolant uses silicates and phosphates to prevent corrosion. European formulations tend to use only silicates, and Asian formulations tend to use only phosphates. Both silicates and phosphates are quick-acting surface reactants that are expended when fresh metal is exposed to the coolant. This is the reason why the coolant must be changed frequently, about every 30k miles - the corrosion inhibitors are used up and the coolant loses it's ability to prevent corrosion. You'll find IAT coolant used in Subarus.

DEX-COOL - an example of an OAT coolant

OAT - Organic Acid Technology

Organic Acid Technology is a corrosion inhibitor that does not use silicates or phosphates - instead they use a combination of organic compounds to coat the surface structure of exposed metal. By forming a molecular coating on top of the exposed metal, the corrosion inhibitors are not expended. This is what gives OAT coolant it's extended service interval of 150k miles and leads to the term "extended-life coolant". One of the downsides of organic corrosion inhibitors is their slower reaction time to coat metal. The most infamous form of OAT coolant is DEX-COOL - GM's preferred coolant which got a bad reputation due to the picky nature of OAT coolant and it's reactivity with iron oxide and engine gaskets. DEX-COOL OAT coolant uses two chief chemicals to provide the corrosion protection - sebacate and 2-EHA - both of which are excellent in protecting exposed metal surfaces from corrosion (especially when hard mineralized water is used). The problem is when DEX-COOL equipped cars have failed radiator caps that fail in the open position. According to GM, when the radiator cap fails open, this exposes coolant to contamination from airborne particles in the engine bay. Of these, iron oxide particles that make their way into engine coolant reacts with the OAT additives and forms the red muck that slowly chokes the cooling system to death. This is combined with the fact that 2-EHA is a powerful plasticizer which reacts with engine gaskets and hoses, causing gasket failure. Modern OAT mixtures such as those used in late-model Asian automakers use formulations that do not include 2-EHA.

Volvo engine coolant, which is a silicated HOAT coolant

HOAT - Hybrid Organic Acid Technology

Hybrid Organic Acid Technology is a relatively new type of coolant that is designed to address and solve the problems of IAT and OAT coolant. HOAT coolant contains silicates or phosphates (or sometimes both) as a quick-acting mechanism for controlling corrosion, and then combine that with sebacate or another OAT technology to provide the long-term protection. Remember, IAT additives like silicates and phosphates are expended when they perform their job - when this is combined with OAT technology where the inhibitors can constantly be reused, this allows HOAT coolant to have the fast-acting protection of IAT coolant, but can be used with long drain intervals of around 135-150k miles. European manufacturers tend to use HOAT formulations with silicates, while Asian manufacturers tend to use HOAT formulations with phosphates. Volvo utilizes a blue phosphate-free HOAT as of late.

Don't rely on dyes

Coolant dyes long ago used to determine what type of coolant was being used - however with modern coolants, the dyes are only added to help leak detection. Don't rely on the color of the coolant to determine what type of coolant it is - in fact, there are largely incompatible types of coolant that may share the same color. It's unlikely that mixing coolant will cause any harm, but generally mixing an extended-life coolant with a traditional coolant will lower the service interval of the entire system to about 30k miles. There have been reports of coolant "gelling" or "sludging" when mixed, especially when DEX-COOL is involved, so the best practice is to not mix coolants whenever possible.


Sources:
Wikipedia - Galvanic corrosion
Wikipedia - Cavitation
Wikipedia - Antifreeze
Wikipedia - Sebacic Acid
Wikipedia - 2-Ethylhexanoic acid
ImperialFleet Publishing - All about Dex-Cool
How-To Matthew - Types of Coolant and Antifreeze
Turbo Diesel Register - Types of Antifreeze For Your Truck
PT Cruiser Forum - Why HOAT?
Pentosin - Antifreeze
AMSOIL Products for SUPERIOR ENGINE PERFORMANCE - Antifreeze Types - from original IAT to new POAT engine coolants
Heart Business Media - Coolant Confusion: It's Not Easy Being Green ... or Yellow or Orange or ...
Recochem Inc - An Introduction to Coolant Technology
Reco-Cool - Technology Based Coolants
Jeep Forum - New to form with Water Pump ???s
Hellafunctional - Things you should know about coolant


About the Author: Andrew Peng

4bc258bba12eb53f892c34317c49b78eAndrew is an aerospace engineer and car fanatic that enjoys working on his garage of Volvos and Subarus. When he's not busy attending car meets and shows or taking things apart, he enjoys driving his cars and finding interesting new ways to break them. He can be reached via his personal website at http://andrewpeng.netFacebook, Google+Instagram, or Twitter.


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Written by :
Andrew Peng

Andrew is an aerospace engineer and car fanatic that enjoys working on his garage of Volvos and Subarus. When he’s not busy attending car meets and shows or taking things apart, he enjoys driving his cars and finding interesting new ways to break them. He can be reached via his personal website at http://andrewpeng.net, Facebook, Google+, Instagram, or Twitter.


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