There are many different systems in an automobile that require O-rings and seals. A single automobile can have over 10 different fluids, each with unique sealing requirements depending on the temperature, pressure, and the type of fluid being sealed. It’s no wonder that an automobile uses so many different type of rubber materials. Below is a list of the different fluids used in a typical vehicle.
- Coolant
- Refrigerant
- Power Steering Fluid
- Windshield Washer Fluid
- Motor Oil
- Automatic Transmission Fluid
- Gear Oil
- Gasoline, Diesel Fuel, Biofuels
- Brake Fluid
Coolant
The cooling system is used to keep the engine at a safe temperature preventing damage to the components from excessive heat caused by engine combustion. Modern cooling systems are cooled with a variety of coolant types designed to absorb heat from the engine and then release that heat through the radiator. The engine coolant (antifreeze) prevents the fluid from freezing or boiling as well as prevents corrosion and lubricates and protect the water pump seals, gaskets and bearings.
Some of main ingredients in coolant are ethylene glycol, silicate, and/or phosphates, although many Japanese vehicles use a silicate-free coolant. Each automotive manufacture has done extensive studies to determine the best coolant to use in their vehicles. Many of these coolants are designated by color. There are green, red, orange, yellow, blue and purple color coolants. Many of these coolants are mixed with water at a 50/50 ratio. However, depending on the vehicle manufacture the may recommend anywhere between 40% to 70% coolant to water ratio. It is recommended that you use the proper coolant the manufacture recommends.
There are three types of coolants, Inorganic Additive Technology (IAT), Organic Acid (Additive) Technology (OAT), and Hybrid Organic Acid (Additive) Technology (HOAT). The older green coolant is an IAT coolant and is ethylene glycol based with silicate as a corrosion inhibitor. More modern, extended life coolants are OAT and are ethylene glycol based but contain a different combination of phosphates and silicates as well as organic acid technology. HOAT coolants are based on traditional IAT and OAT technology containing a mixture of mineral and organic corrosion inhibitors.
The good thing is most rubber elastomers are compatible with ethylene glycol based coolants except polyacrylate and polyurethanes. In my personal vehicles I’ve seen EPDM and Nitrile rubber O-rings and seals.
My preference is EPDM as its still cost effective compared to silicone or fluorocarbon (FKM) O-rings and seals and it has a broader temperature range than Nitrile and FKM elastomers. Nitriles have a usable temperature range around -40°C to +100°C and FKM -15°C to +230°C where EPDM elastomers will work at colder temperatures, -55°C, and a high temperatures around +125°C. EPDM can be easily manufactured in softer materials to help seal porous surfaces often found cast engine water pumps, thermostat housing surfaces. EPDM is also the preferred elastomer for sealing water and steam. EPDM is extremely weather and ozone resistant, however, it’s not compatible with petroleum based oils and greases.
Nitrile works well with coolant systems. It has a temperature range from around -40°C to +100°C and can handle temperatures to +121°C for short periods of time. Nitrile not only works well with water, it’s resistant to most oils, hydraulic fluids and greases. Nitrile is a tough material with good compression set properties, meaning it doesn’t easily take a set, become flattened, when compressed over time. However, consistent exposure to temperature above its max temperature can cause it to take a compression set.
Silicone elastomers have a broad temperature range from as low as -65°C to over +200°C, with some special silicone compounds able to meet +315°C. Silicone is a weak material. It typically has low tensile strength and low tear resistance, therefore, it’s not recommended for dynamic seals but is great for static seals. Silicone has great compression set properties that are comparable to Nitriles and better than EPDM elastomers.
MVAC Refrigerant
R12 was the refrigerant used in automobiles prior to the 1990’s. In the late 1980’s automotive MVAC manufacture start moving away from the ozone depleting chlorofluorocarbons (CFC, dichlorodifluoromethane ) known as R12 and switching to hydrofluorocarbon (HFC, 1,1,1,2-Tetrafluoroethane) know as R134A refrigerant because of their lower ozone depleting and global warming potentials and it has a similar pressure-temperature relationship as the R12 refrigerants making diagnostics for the mechanics the same for both types of systems.
Nitrile rubber was commonly used in the older R12 (Chlorofluorocarbon, CFC) automotive MVAC systems. Nitrile could easily withstand the low and high temperatures of the system along with being resistant to the lubricating oil that we used. In 1987 the U.S. and several other countries signed the Montreal Protocol which agreed to phase out CFC’s. CFC’s were also used in refrigeration units, aerosol cans, foam food packaging, fire extinguishers, and asthma inhalers. CFC’s have been banned in the U.S. Since 1996 and eventually banned globally in 2010.
In the late 1980’s and early 1990’s, R134A (Hydrofluorocarbon, HFC) replaced R-12 in automobile MVAC systems because HFC’s had a substantially lower Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) than CFC’s. In 2013 DuPont and Honeywell developed and released R1234YF, a hydrofluoroolefin (HFO) that has an ultra-low GWP. R134A will be no longer be used in the U.S. in light-duty vehicles starting with model year 2021, globally starting with model year 2025.
When the automotive industry started using R134A they switched the type of rubber material used in the MVAC systems. My understanding was they wanted to use a rubber material that was more resistant to the possibility of the refrigerant permeating through the rubber. Although R134A had considerably lower Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) than the CFC’s, MVAC manufacturers wanted to minimize the potential for leakage into the atmosphere. In the late 80’s early 90’s when the automotive industry started equipping vehicles with R134A MVAC systems, Ford Motor Company went to a Hydrogenated Nitrile (HNBR) with a green color. The green color was used to help the mechanics identify R134A components vs. R12 components. General Motors went to a low temperature polychloroprene (Neoprene®) material and used the color blue. However, now EPDM and HNBR are the choice rubber materials or use with R134A refrigerants.
In 2011 the EPA approved the new environmentally friendly R1234YF refrigerant jointly developed by Honeywell and DuPont. R1234YF has a GWP that is 335 times less than R134A. The new refrigerant and was tested extensively to ensure it meets critical automotive standards. EPDM and HNBR are the rubber materials being used in R1234YF refrigerant.
EPDM elastomers are price competitive and meet the critical requirements of automotive industry for MVAC systems. EPDM has lower operating temperature range and is more cost effective than HNBR.
Windshield Washer Fluid
Windshield washer fluid is special designed to clean windshield of bugs, road grime, salt, snow, and frost while lowering the freezing point of the solution. It can be dangerous to drive without washing fluid especially in colder climates.
Windshield washing fluid can contains methanol or ethanol, isopropanol, and ethylene glycol found in antifreeze. In 2018 the use of methanol in windshield washing fluid was banned in the European Union and now most washing fluids are based on ethanol.
When looking at what rubber material is compatible with methanol, ethanol, isopropanol, and ethylene glycol, the most cost effective material is EPDM. EPDM is cost effective and readily available in O-rings and seals. EPDM elastomers will work at colder temperatures, -55°C, and a high temperatures around +125°C. EPDM is also the preferred elastomer for sealing water. EPDM is extremely weather and ozone resistant, however, it’s not compatible with petroleum based oils and greases.
Butyl, chloroprene (Neoprene®), isoprene and natural rubber are other materials that are compatible with methanol, ethanol, isopropanol, and ethylene glycol found in windshield washing fluid. The choice of elastomer will most likely depend on availability, cost, and if it’s an off-the-shelf O-ring, extruded tube, or molded seal.
Motor Oil
There are many seals on the automotive engine that seal motor oil. There are valve cover gaskets, oil pan gaskets, covers, manifold gaskets, various sensor gaskets. There are a several basic types of motor oil, conventional, semi-synthetic and full synthetic. Conventional oil (mineral oil) can provide adequate protection in the automotive engine. They are more cost effective than synthetics, however, they’re less chemically stable, they can break down quicker and oxidize easier than synthetic motor oils. Synthetic motor oils use a higher refined base oil than conventional motor oils. They have superior qualities and last longer than conventional motor oils. In the middle there are semi-synthetic motor oils which are a combination of conventional and synthetic motor oils and typically cost less than a full synthetic motor oil. Because a majority of the cars on the road today have over 75,000 miles, oil manufacturers have created high-mileage oil specifically blended for higher mileage vehicles.
Motor oils come in various viscosities. Viscosity is the measure of a fluids resistance to flow. Motor oils tend to thicken when cold and thin when hot, therefore, motor oils come with a multi-viscosity rating such as 10W-30. Oil is rated at zero degrees and at 212°F. The number preceding the “W” (for winter) is flow rating at zero degrees. The lower this number the better flow at cold temperatures. When the oil heats up it becomes thinner. This rating is represented by the number after the “W”. The higher this number the thicker the oil will stay at higher temperatures. In cold climates you don’t want an oil that is too thick and vice-versa in hot climates.
There are many additives added to improve motor oils performance. There are viscosity-index improvers, dispersants, friction modifiers, detergents, pour-point depressants, antioxidants, foam inhibitors, rust and corrosion inhibitors.
Nitrile rubber is a good for use with motor oils. It is resistant to oils and greases and has a broad temperature range from around -40,C to +100°C and can withstand short periods of time at +121°C. The only downfall is that some areas of the engine may exceed the high temperature rating of Nitrile. HNBR will provide increase temperature range than standard Nitrile. This material is usable at a lower temperatures and higher temperatures than Nitrile. HNBR has a temperature range from -55°C to +150°C. However it is more costly than standard Nitrile.
Polyacrylate has a temperature range from around -10°C to +150°C. Polyacrylate has excellent compatibility with motor oils and is ozone resistant and is more cost effective than fluorocarbons. It’s used extensively in automatic transmissions and some engine seals and hoses.
Another alternative is Fluorocarbon (FKM). Fluorocarbon has excellent resistance to motor oils and greases. Fluorocarbon can be used where high temperature resistance is required. Fluorocarbon has a temperature range from about -15°C to over +200°C. There are low-temperature fluorocarbons available that is usable down to -40°C. Fluorocarbon is used a lot in the fuel system because it’s compatible with gasoline and diesel fuels. Special blends of fluorocarbon are required for biofuels.
Automatic Transmission Fluid
Automatic transmissions are a challenging environment for rubber seals. With more powerful engines, transmissions can run extremely hot. Automatic transmission fluid is designed to absorb heat from the transmission components and clutches and release the heat in the transmission cooler. However, transmission fluid has its heat limitations. Generally the hotter the fluid runs the the shorter the life of the fluid.
Automatic transmission fluid types include Dextron VI(GM), Mercon V(Ford), and ATF+4 (Chrysler). These are the most common automatic transmission fluids on the market. Older Ford automatic transmissions, up into the 1980’s, used a Type F fluid. Type F fluid has since been replaced with Mercon type fluid. Other types of automatic transmission fluids include multi-vehicle synthetic and continuously variable transmission fluid. Multi-vehicle synthetic transmission fluid were designed to be used with a wide range of automatic transmissions and provide superior performance and protection. Continuously variable transmission fluid is special designed for the new demands of the continuously variable transmission (CVT) that rely on high steel on steel friction to transfer power.
Polyacrylate (ACM) is the the rubber material used in automotive engines and automatic transmissions. Polyacrylate rubber offers excellent long term heat resistance compared to other elastomers. Polyacrylate is resistance to weathering and ozone and has excellent resistance to petroleum and synthetic lubricants.
Another alternative is Fluorocarbon (FKM). Fluorocarbon has excellent resistance to hydraulic fluids and greases. Fluorocarbon can be used where high temperature and chemical resistance is required. Fluorocarbon has a temperature range from about -15°C to over +200°C. There are low-temperature fluorocarbons available that are usable down to -40°C.
Gear Oil
Manual transmissions, transfer cases and differentials commonly use gear oil. Some manual transmissions and transfer cases use motor oil or ATF fluid depending on the type and manufacture of the unit. Always use the manufactures recommended fluid or oil.
Gear oil has extreme pressure properties to protect the spiral, bevel, and hypoid gears from wear caused by metal to metal contact. Gear oil also has inhibitors to protect bearing surfaces from rust or corrosion and prevent foaming. Gear oils are designed to operate at low and high temperatures. They work under hydrodynamic lubricating conditions which means they provide an oil layer between metal surfaces on the gears and bearings during operation. These lubricants can work under pressures that exceed 350,000 pounds per square inch (psi).
The American Petroleum Institute (API) established a service classification for gear lubes from GL-1 through GL-5. GL-1 through GL-3 class are for use with lighter load spiral and bevel gears. GL-4 and GL-5 class is for use with automotive equipment. GL-4 is used in transmissions. GL-4 is more suitable for brass alloys commonly used in manual transmissions while GL-5 class contains extreme pressure additives commonly required for used with hypoid gears located in the differential.
The Society of Automotive Engineers established a classification system by viscosity grades such as 75W90. 75W is the low temperature rating. The lower the “W” number the better the lube functions in cold weather. The high number, “90” is the viscosity measured at 212°F. The larger the high number the thicker (more viscous) the gear oil.
There are several common elastomers that work with gear oil. Nitrile (petroleum based only), fluorocarbon (FKM), chloroprene (Neoprene®), and silicone; although silicone may exhibit some minor effect and I would recommend it only be used on static seals due to the weak characteristics of the material. Nitrile has good resistance to petroleum based hydraulic oils, however it’s not recommended for use with synthetic hydraulic oils.
Fluorocarbon (FKM) elastomer has great chemical and high temperature resistance. It has excellent compatibility with both synthetic and petroleum hydraulic oils. FKM elastomers have an operating temperature range from -15°C to +230°C and can be compounded to meet -40°C.
Chloroprene (CR, Neoprene®) elastomers exhibit good abrasion, chemical, flex, heat, oil, weather and ozone resistance. It’s good in dynamic applications because of its toughness. Chloroprene has an operating temperature range from around -15°C to +100°C and can be compounded to meet -40°C.
Silicone has the broadest temperature range from -65°C to +400°C. Silicone is thermally stable which their physical properties stay consistent over a wide temperature range. Silicone is a weak material with low tensile strength, abrasion and tear resistance, however is exhibits good compression set properties and resilience. It’s recommended for static seals only.
Gasoline, Diesel Fuel, Biofuels
Gasoline is a mixture of various hydrocarbons and additives. Hydrocarbon based fuel are produced from refined petroleum crude oil. Conventional gasoline is a blend of more than 200 different hydrocarbons ranging from those containing 4 carbon atoms to 11 or 12 carbon atoms arranged in various combinations.
One of the most important characteristics of gasoline is its octane rating. The higher the octane rating of gasoline the more stable the gasoline. In a gasoline engine, the ignition and burning of the fuel is controlled. The fuel is ignited and burns from one end of the cylinder to the other end in a controlled manner. High cylinder temperatures and pressures can cause the fuel to spontaneously combust, also called pre-ignition and detonation, that causes a knocking that sounds like marbles rattling in the engine, poor performance and poor fuel economy. Increasing the octane level in the gasoline helps slow the combustion down and allow it to ignite in a more controlled manner. Today’s higher performing engines require a higher octane rated gasoline.
In the past there have been several methods of achieving higher octane rating in gasoline. In the early 20the century tetraethyl lead (better known as lead) was added to gasoline to increase the octane rating. Tetraethyl lead was preferred over other methods using benzene (aromatic hydrocarbons) and alcohols such as ethanol because it was cheaper. Tetraethyl lead was phased out due to health concerns from the lead coming out of the tailpipe of automobiles. After the phasing out of lead refineries had 2 choices, increase the use of aromatic hydrocarbon mixture of benzene, toluene, xylene and ethyl-benzene (BTEX) or ethanol. Later it was found that incomplete combustion produced ultra-fine particles and polycyclic aromatic hydrocarbons (PAHs) which cause reproductive, developmental and other adverse health effects.
Today, refineries are using ethanol as an octane booster to produce E10, 10% Ethanol mixed with 90% gasoline. Ethanol allows refineries to use lower octane gasoline and use the ethanol to increase the octane rating to the labeled value.
Diesel Fuel
Petroleum distillate fuel oil, aka diesel fuel, comes from refined crude oil. Diesel fuel is used in compression ignition engines, also called diesel engines, which is named after the inventor Rudolf Diesel. Diesel engines work under compression ignition and do not have spark plugs as in conventional gasoline engines. The diesel fuel ignites under compression when injected into the cylinder. The important characteristic of diesel fuel is its cetane index. The cetane number is the measure of the quality of the diesel fuel. The higher the cetane number, the easier the diesel fuel ignites under compression ignition. This allows for easier starts, more complete combustion which means more power and less harmful emissions. As we discussed earlier in gasoline’s octane rating where the higher the octane rating the less likely the gasoline will ignite under compression, the higher cetane the easier it is to ignite under compression.
Biofuels
The advantages of biofuels are they produce less greenhouse gasses, reduce our dependency on foreign oil, are they are renewable. Biofuels, conventional and advanced, are a renewable liquid energy source from agricultural; crops, waste, forest products vegetable oils, fats and greases. Conventional, 1st generation, biofuels are made from agricultural crops. There are two types of conventional biofuels, ethanol and biodiesel. Ethanol is made form the sugars found in grains such as corn or barley and blended with conventional gasoline at 10% to make E10 gasoline and 51% to 83% to make E85 for flexible fuel vehicles.
Biodiesel is made from vegetable oils, fats and greases and blended with petroleum diesel fuel at any percentage. The most common blend is B20 biodiesel that is a blend of 20% biodiesel and 80% petroleum diesel fuel. B100 is pure biodiesel.
Petroleum companies are researching 2nd generation biofuels, also called advanced biofuels, that are made from algae, waste, forest products and made with non-food feedstock that is less expensive and doesn’t compete with food sources as the 1st generation biofuels made from agricultural crops. 2nd generation biofuels are a “Drop-in” replacement for petroleum based fuels that can be used in existing automobiles. Advances biofuels are most likely to become the primary source of biofuels.
3rd generation biofuels are being researched and include algal biofuels and synthetic biofuels. Algal biofuels are grown in ponds and harvested and then converted into biofuels. They yield up to 10 times more per acre of land than 1st generation biofuels and do not compete for land or potable water as 1st generation biofuels. The concept of Synthetic biofuels are to genetically modify the algae to synthesize biofuels directly in their cells.
Fluorocarbon (Viton®, FKM) is the most common elastomer used with diesel fuels. FKM has excellent chemical and heat resistance. Standard FKM (Type A), a copolymer vinylidenefluoride (VF2) and hexofluoroproplene (HFP) with a bisphenol cure, has a temperature range from around -15°C to over 200°C with higher grade fluorocarbons able to meet -40°C. There are several other types of fluorocarbon elastomers to meet different environments such has Type B (Viton® B) and Type F (Viton® F) which are terpolymers of VF2, HFP, and tetrafluoroethylene (TFE) with a bisphenol cure. Type F was designed for use in oxygenated fuels and modern lubricants. Type F (and type GF with peroxide cure) is resistant to Methanol and Ethanol found in today’s fuels. FKM (Viton®) Type F was designed for use with biofuel systems.
Nitrile (NBR, BN) has excellent resistance to diesel fuels, greases, and oils and is more cost effective than fluorocarbon. Nitrile has a temperature range from around -40°C to +100°C. However, Nitrile has poor resistance to Ethanol.
Brake Fluid
Brake fluid us used to transmit power from the brake pedal to the brakes on the vehicle. It’s not uncommon for brake systems components to reach 400°F to 500°F during extreme conditions. Not only must brake fluid transmit power, handle heat, but it also provides lubrication and prevents corrosion of the internal hydraulic brake parts.
Dot 3, Dot 4, and Dot 5.1 brake fluids are composed of 60% to 90% polyglycol esters and/or borate esters solvent, 5% to 30% polyglycol lubricants, and 2% to 5% additives such as corrosion inhibitors, anti-oxidants, and anti-foam inhibitors. These brake fluids are hygroscopic, meaning it absorbs water and moisture that can contaminate the brake system and cause corrosion. Dot 3 is polyglycol ester based; Dot 4 is polyglycol ester with borate ester, Dot 5.1 is borate ester based with polyglycol ester blended in.
Dot 5 brake fluid is a silicone based brake fluid typically used on race cars and classic cars that may sit in storage. Dot 5 will not absorb water or remove paint like polyglycol ester based brake fluids will. However, silicone brake fluids are lighter than water and over time water contamination could pool in the lowest part of the system, typically the calipers. Under heat, this water will vaporize and a spongy brake pedal or loss of braking could occur.
There are 4 material that are compatible with polyglycol ester brake fluid, EPDM, Chloroprene (CR, Neoprene®), Styrene Butadiene (SBR), and Natural Rubber (NR). EPDM and CR have excellent resistance to the polyglycol ester brake fluids and SBR and NR with fair resistance that is usually okay to use in static seal applications only. EPDM is excellent for internal seals while CR is good for use with brake lines. EPDM is not compatible with greases or oils, therefore, where resistance to brake fluid as well as greases and oils is required, such as brake lines, Chloroprene (Neoprene®) would be a good choice.
