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The ‘Other’ Gaskets
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By Counterman
Terminology is one of the hurdles we face day in and day out in the automotive industry. It varies between automakers, parts suppliers, technicians and consumers. Gaskets and seals are some of those terms that are easily mixed up from time to time. So, what’s the difference between a gasket and seal, since they’re both designed to do the same thing?
A gasket is any material installed between two fixed components with flat sealing surfaces, designed to conform to minor surface irregularities and prevent any liquid or non-liquid that passes between the components from going anywhere other than its intended location. In this case, liquid can be oil, coolant, transmission fluid, power-steering fluid, gasoline … you get the idea. Non-liquid refers to air, exhaust or fuel and crankcase vapors. Gaskets can be made of paper, cork, rubber, steel, aluminum, copper or a combination of materials.
A seal, at least in most cases, is made of rubber. The main differentiator, however, is not material but application. Gaskets are compressed tightly between two fixed components, whereas a seal is not tightly sandwiched or compressed in the same manner (at least most of the time), since it must allow movement of one of the components.
It’s easy to get deep in the weeds here, because a seal, by most accepted definitions, is used between a fixed and a moving component. Getting even more “technical,” this is called a dynamic seal, and a gasket can be referred to as a static seal. So, one is the other?! Well, I’ll try to keep the grass as short as possible.
The easiest way to grasp it all is by looking at some examples. Common gaskets are head gaskets, valve-cover gaskets, thermostat-housing gaskets and exhaust-manifold gaskets, just to name a few. The components they seal between are bolted or held firmly to each other.
Gaskets have the advantage of sealing high pressure, such as that built during the compression stroke or in the cooling system, and depending on material, they can handle extreme heat, such as exhaust-manifold gaskets. Seals, on the other hand, can’t handle the same amount of pressure, and rubber can’t handle extreme heat.
Examples of common seals are crankshaft and camshaft seals, transmission input and output shaft seals and axle seals. The common link is the fact that all these components rotate. But get ready to fire up the weed-eater.
If all that’s true, what’s the difference between a thermostat-housing gasket and a thermostat-housing seal? A thermostat gasket is a thin, paper-type material that installs between the housing and the intake manifold, block or wherever the housing is mounted. In most cases, the housing is made of metal. Then, as plastics became more common for use in automotive components, thermostat housings were one of the first things to change over.
Plastic is less expensive and easier to manufacture, and it’s lighter-weight. Plastic thermostat housings, however, required an O-ring seal instead of a gasket, for many reasons. Plastic wasn’t strong enough to handle the same amount of torque as a metal housing, so the lower torque required to prevent cracking the plastic meant a gasket would be less effective.
Rubber O-ring seals compress when tightened, and an advantage of rubber lies in its elastic properties, meaning it always wants to return to its original shape. This causes a rubber O-ring to keep constant tension outward equally in all directions. Another advantage of a rubber O-ring in this case is the expansion rate of metal and plastic is very different. Use of an O-ring allows an increased range of movement while maintaining a positive seal.
Many cooling-system quick-connect hoses and bypass tubes utilize rubber seals. The reason is not only the elasticity of the O-rings, but also the fact that when a rubber seal is used between two components, it allows a certain amount of “float” between them during expansion and contraction, maintaining a positive seal with no stress on the components.
I mentioned earlier that most seals are made of rubber. It’s likely true to say all of them are today, but years ago before we had developed good rubber technology, seals were made of felt, leather and, in some cases, asbestos. It was the only way to bridge the gap between a fixed and moving component and keep it from leaking, at least for the most part.
Prior to the advantages of today’s rubber technology, vehicles often were equipped with two-piece crankshaft seals. These were considered “rope” seals, simply because they looked like a piece of rope. Many of these were made of asbestos. One piece was installed in a groove in the engine block, and the second piece was installed in the bearing cap.
It required very careful work to install these successfully with no leaks, and it proved to be very difficult over the years. If you’re around old cars often, you know that classic-car owners often keep a large piece of cardboard underneath to catch offending drops of oil that in most cases come from a two-piece crankshaft seal. Eventually, auto manufacturers switched over to one-piece crankshaft seals to eliminate this problem, and many old engines can be retrofitted to a one-piece seal.
The bottom line is that seals are used because they allow movement of components while keeping constant tension against them. To aid in sealing, most shaft seals have a small spring on the inside of the sealing lip to assist in keeping tension against the moving component.
O-ring seals are used because they keep constant tension between components while allowing expansion and contraction. This is why O-ring seals are used in air-conditioning systems, and O-ring seals such as this have the ability to handle a higher pressure.
Is there a difference between a gasket and a seal? Absolutely. Is there gray area? Sure. You can dig even deeper with head gaskets that are made of one material yet feature rubber seals around coolant passageways. This is a gasket with seals incorporated in certain areas to take advantage of the benefits of elasticity in the rubber.
Above all, whether your customer asks for a gasket or a seal, you know one thing: They’re trying to stop a leak. That means they need the parts; fluid to replenish what was lost; and shop rags and cleaners to clean up the mess!
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By CarPartAU
2010 MAZDA CX9 ENGINE / MOTOR FOR SALE WITH WARRANTY
OTHER MAZDA PARTS PLEASE INQUIRE BELOW OR CALL
Date Listed:27/03/2020 Last Edited:27/03/2020 Make:Mazda Warranty:available Condition:useD Visit us @ link hidden, please login to view.
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By CarPartAU
Date Listed:27/03/2020 Last Edited:27/03/2020 Make:Mazda Warranty:available Condition:used Visit us at link hidden, please login to view
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By APF
It’s been more than a decade since the federal government first mandated that new vehicles feature tire-pressure monitoring systems to warn drivers against underinflation. Direct TPMS sensors and their service kits are a common stocking item for parts stores, tire shops and even general repair shops nationwide, but while these sensors are now well-known and widely available, there is another system that provides tire-pressure monitoring without sensor service and replacement.
In the case of direct TPMS, radio frequency signals from each tire-mounted sensor are transmitted to a central receiver, where the individual air-pressure readings are compared to the manufacturer’s recommended inflation pressure. If the actual pressure in any tire drops below 75 percent of this recommended calibration, the warning light will illuminate. Some manufacturers also display the actual pressure of each tire in their driver information center (usually found in the gauge cluster) during startup.
Indirect TPMS, as its name implies, does not use a direct “PSI” reference to calculate tire pressure. Instead, this system estimates any pressure differentials based on vehicle and wheel speed, as well as tire size. Indirect TPMS piggybacks on the ABS and traction-control system, using the information from these sensors to determine if an individual tire is underinflated. The theory behind indirect TPMS is that the circumference of a tire decreases slightly as it deflates, and the rolling resistance of the tire increases. By using individual wheel-speed sensor information, the system can detect the difference between an underinflated tire and a properly inflated tire. Onboard software can calculate just how much difference exists between wheels, and based on the manufacturer’s recommended tire size, make a determination on the percentage of underinflation, and trigger the warning light at the same 75 percent threshold.
It is a cost-effective system for manufacturers, with no additional hardware in terms of sensors and receivers. It can represent a long-term savings to consumers who otherwise would periodically replace battery-operated sensors and service kits, and for drivers who have multiple sets of tires for their vehicle. Many Northern drivers maintain a full set of “winter wheels” with snow tires, rather than dismounting tires each season. Sports car enthusiasts may also maintain a set of “track wheels” for weekend racing, with some sanctioning bodies requiring functional TPMS as part of their safety inspection. Finally, any “tire buster” tasked with mounting and dismounting tires at the local tire shop can tell you that with indirect TPMS, it’s a relief not to have to worry about breaking off a sensor during tire service.
Of course, indirect TPMS has limitations, as seen in the first crop of indirect TPMS-equipped vehicles in the late 1990s and early 2000s. These systems could only sense if a single wheel was underinflated, as it compared the individual tires to each other. If all four tires were uniformly underinflated, all four speed sensors would have the same values. No warning would be given, even if the tires were severely low. These systems also required a four-channel, four-wheel anti-lock brake system to operate, which was not widely used with light trucks or rear-wheel-drive passenger cars at the time.
Indirect TPMS also requires recalibration any time tire pressures are adjusted, or when tires are rotated or replaced. These systems also may give false warnings in wet or icy conditions, as the rotation of slipping or spinning tires will differ when they break traction. It also relies on all of the monitored tires being the same size, with accuracy being compromised when larger- or smaller-than-stock tires are fitted to the vehicle. Finally, indirect systems cannot function while the vehicle is stationary, leaving the driver unaware of a potential problem until after the vehicle is already in motion.
While older systems also lacked the ability to identify which tire was underinflated, advancements in wheel-speed sensor technology have made this an available feature on many newer vehicles equipped with indirect TPMS. They are considerably more accurate than previous designs and can be found on several modern import nameplates, including various Audi, Honda, Mazda and Toyota models.
Although indirect TPMS is a less expensive option for the manufacturers, and it does have a simplicity of design, direct TPMS is still a more widely used and accurate system, with the added benefit of requiring us to provide a steady supply of replacement parts to our customer base.
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