Information for Maintaining your Automobile
Hope the information on this page provides some insight on the various areas of your car.
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All About Oil Leaks
From CanadianDriver:
April 10, 2002
by Jim Kerr
One of the most frustrating vehicle ownership experiences is when your vehicle marks its territory on your driveway or garage floor with a puddle of oil or antifreeze. Even small leaks can cause damage if not repaired, so why can't the manufacturers develop leak proof engines and transmissions? Compared to vehicles even 10 years old, new vehicles are sealed much better. New seal materials and technology have helped considerably, but the working environment still has a large impact on the effectiveness of seals and gaskets.
There are five things requiring sealing on an engine: oil, coolant, fuel, compression, and dirt. Yes dirt - some things need seals to keep them out, not in. Two kinds of materials are used to contain these fluids - seals and gaskets.
Rotating shafts, such as crankshafts or belt-driven camshafts use lip-type seals to hold the oil in. These are sometimes referred to as "dynamic seals" because the part is moving inside the stationary seal. Even small oil leaks past a camshaft seal can destroy rubber timing belts and cause the engine's valves to be bent. This is one place not to scrimp on repairs!
Many seals will have two sealing lips - one to keep the oil in and another facing the opposite way to keep dust and dirt away from the oil seal side. When dirt gets into a seal, it embeds in the softer seal surface and then acts like a grindstone on the hard metal shaft turning inside the seal. A groove wears into the shaft and a leak starts. Some parts, for example - front crankshaft damper pulleys, can sometimes be repaired by installing a "speedy-sleeve". This thin metal band is pressed over the worn groove so the seal has a new surface to ride on. It is also possible to build up worn surfaces by spray welding and then grinding them back to specifications, but this is expensive and only used for rare or high priced parts. Most automotive parts are relatively cheap, so worn ones are usually replaced.
Gaskets have changed a lot in the last few years. Some cheap aftermarket gasket sets still use cork. Cork relies on oil seeping into the gasket to make it swell and seal. Sealers should never be used when installing cork gaskets. Rubberized cork gaskets were a big improvement in sealing, but most new gaskets are made of synthetic rubber. RTV silicone has been used to make gaskets, but its use is decreasing. It must be installed on a clean, oil-free surface and this makes it difficult for some service applications.
The biggest problems with gaskets have been distorted gasket mating surfaces and over-tightened bolts. Stamped steel engine covers have mostly been replaced by moulded plastic or cast aluminium covers. These both offer more even clamping of the gasket and don't distort as easily. Many new gaskets have internal metal spacers moulded into the material to prevent over-tightening the gasket.
Head gaskets and intake manifold gaskets have a very difficult job to do. Head gaskets seal engine compression, coolant, and sometimes oil. Intake gaskets need to seal air, fuel vapours, and coolant. Aluminum engine parts have made the sealing job even harder. Aluminum expands about .006inch for every inch of material, for every 28C change in temperature. An average cylinder head could expand nearly ½ inch in length from a cold winter start to full operating temperature. If the gaskets were attached solidly to the parts, they would be ripped apart by the expansion. Instead, the gaskets are made to allow the parts to slide on each other as temperatures change.
Many bolts used to hold critical engine parts together are now of the "torque to yield" type. This means the bolts stretch as they are tightened and remain in an elastic state to allow parts to move. Torque to yield bolts are designed to be used only once. After that their elastic ability is limited, so new bolts must be used each rebuild. Use the wrong bolts or torque and gaskets fail, causing head gasket compression leaks, warped heads, and coolant leaks.
Coolant leaks should be checked immediately. External leaks leave stains and puddles, but sometimes they can leak internally as well. Even a couple ounces of antifreeze mixed in the engine oil will start to destroy engine bearings.
There are thousands of types of sealers, gaskets, and seals. The key to maintaining a leak free engine is to use the correct product for the application, tighten it to specifications, and make sure everything is clean and straight before putting it together. With care, even older engines can remain as leak free as many new engines are.
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Why brake pulsations happen (and what you can do about it)
From CanadianDriver:
January 8, 2002
by Jim Kerr
Brake pulsation has become a common concern on many newer vehicles. The vehicle stops smoothly when new, but after a few thousand kilometres the brake pedal starts to pulsate when stopping, the brakes feel like they are grabbing and releasing, and smooth stops are impossible. Sometimes the problem starts after the wheels have been removed. This was seldom a concern on vehicles in the 70's and 80's, so what has changed to make it a problem today?
The answer is weight. To increase fuel efficiency of new cars and reduce manufacturing costs, the accounting department (often referred to as the "bean counters") ensures every part of the vehicle has its weight reduced as much as possible. This works fine for most parts but ask a brake system engineer about brake rotors and you will hear that heavier is better. Heavier brake rotors can absorb more heat, so they fade less and give better braking performance. Heavier rotors also tend to be more stable, so they seldom warp, which is one of the causes of brake pulsation.
Sometimes the brake engineers get their way; other times the bean counters win and the brake rotors are built lighter. That is when problems may occur. Sure, they could build brake rotors that are light, powerful, and stable. Carbon fibre and ceramic rotors are available and used on racing cars but the costs would be prohibitive for most passenger vehicles. Porsche does offer a high performance brake option on their 911 Turbo model. This car stops in amazingly short distances with their stock brake system. I can't imagine how much better the brake option could be!
So most of us are stuck with conventional cast brake rotors. If they are not handled correctly, they can warp and that is the beginning of brake pulsation. A warped rotor wears unevenly from side to side as it rubs against the brake pads, and soon the sides of the rotor are no longer parallel to each other. Tolerances for parallelism are often less than .0005 inch maximum, or about 1/4 the thickness of a hair. When the rotor sides are not parallel, the pistons in the brake calipers that apply the brake pads are pushed in and out rapidly. This rapid motion is transmitted through the brake system and into the pedal. We feel it as a pulsation.
Changing a tire is one common cause of rotor warpage. If there is any dirt, rust, or corrosion between the wheel and the brake rotor, it will be clamped unevenly when the wheel is installed and the rotor will warp.
Incorrect tightening of the wheel nuts also can warp a rotor. When installing a wheel, snug up the wheel nuts and then tighten them in two stages using an alternating criss-cross pattern. Using a torque wrench is critical on modern vehicles. Some shops tighten wheel nuts with air impacts. Others use "torque sticks" designed to limit the torque on the nuts. Neither is accurate enough for today's cars. Make sure they use a torque wrench. If you experience brake pulsations after changing a wheel, loosen the wheel nuts and retorque them. If this is done as soon as possible, the rotor will usually correct itself. Leave it too long (more than 1000 km) and it remains warped.
Another cause of brake pulsation is brake rotor run-out. Many manufacturers allow the rotor and hub to wobble up to .003 inch because of machining tolerances. More than that and the rotor wobbles too much - it acts like it is warped. Some cars are especially sensitive to rotor run-out. If it is more than .001 inch, then brake pulsations can occur.
The answer is to correct the run-out to less than .001 inch. One way to do this is to machine the rotors in place on the car instead of using off-car brake lathes as most shops do. This will correct for run-out in both the rotor and the hub. The trouble with this is on-car brake lathe machines tend to be more fragile and cost three to four times an off-car brake lathe so very few repair shops own one.
Recently, another method of correcting rotor run-out has been introduced to the market. Brake Align(r) has designed special tapered shims that are placed between a removable rotor and its hub to compensate for rotor run-out. Run-out is measured on the rotor and one of three different size shims is installed. Run-out can be corrected to within .001 inch.
Brake Align(r) shims have been tested for hundreds of thousands of kilometres and research by the company shows that if rotor run-out can be kept under .001 inch, then brake pulsations are no longer a problem.
Correcting brake pulsations or preventing them is just a matter of details. Keep mounting surfaces clean, machine rotors so the sides are parallel, reduce rotor run-out to a minimum, use the proper procedure to torque wheel nuts, and brake pulsations should no longer be a problem on your vehicle.
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How to Eliminate A/C Odors
From Canadian Driver:
April 24, 2002
by Jim Kerr
Although summer is not quite with us yet, the warm sun quickly heats up a vehicle interior. Many drivers turn on the air conditioning for a few minutes when starting the vehicle to bring the temperature down. The first caresses of cold air bring comfort, but sometimes they are accompanied by a "musty" smell. Usually the musty smell disappears in a few seconds, but sometimes it will persist as long as the air is blowing. Persistent musty smells are unpleasant, but there are ways of correcting it.
To understand why musty smells occur, and how to prevent them, an understanding of the refrigeration cycle of the a/c system will help. When the system is turned on, the compressor (a pump driven by the engine) pushes the refrigerant, usually R134a or R12, to the condenser in front of the radiator where it is cooled and turned into a liquid. This liquid flows through a hose to the evaporator unit (like a small radiator) located inside the heater housing where it expands into a vapour and absorbs heat from the air passing through the fins of the evaporator.
The refrigerant is then pulled back into the compressor to repeat the cycle again. This is a simplified description. Control valves, pressure switches, driers, filters, and accumulators also are needed to make the system work properly but their operation only controls the basic refrigeration cycle described previously.
Water vapour, present in the air, condenses on the cool fins of the evaporator in a manner similar to the water that forms on a cold glass jar removed from a refrigerator. This water traps dirt from the outside air as it passes through the evaporator fins on its way to the passenger compartment. Normally this water and the dirt trapped in it runs into the bottom of the heater-a/c housing and drains through hoses leading beneath the vehicle. The liquid we see leaking beneath many vehicles on a warm summer day is actually this water.
If the vehicle has been operated in a dirty or dusty climate, all the dirt may not be washed away. It can collect in the bottom of the housing or on the evaporator fins and become a perfect place to grow mould and mildew. This is the cause of a persistent musty smell.
There are two recommended methods of removing the musty smell. The most expensive method is to remove the evaporator unit and physically clean it and the heater-a/c housing. The second method is to spray the inside of the housing with a disinfectant to destroy the mould. Both methods may be required to control an odour. I would try the disinfectant method first. Cleaning the evaporator can restore weak air conditioning airflow too.
The disinfectant is often sprayed into the heater-a/c housing through the opening where the blower motor resistor block is mounted. The resistor block must be unbolted, but leave it connected to the wiring. The blower motor must be running during the cleaning process. Caution! The resistor block gets very hot during operation. Spray the disinfectant into the heater housing and onto the evaporator unit, but be sure not to spray any onto hot engine surfaces. Disinfectant solutions specifically to destroy AC mould are available through most automotive parts suppliers and dealerships.
Ventilate the interior of the vehicle with auxiliary fans while spraying the disinfectant. Then let the vehicle sit for five minutes, and rinse the housing by spraying clean water (minimum of 2 1/2 litres) through the opening. Finally, turn the fan off and reassemble the resistor block.
Preventing mould build up in the housing can be difficult. Check the drain tubes and unplug them if required. General Motors has designed an accessory afterblow module Part #25533406 to help prevent odours from developing. This module turns the heater fan on five minutes after the ignition has been off for fifty minutes and the air conditioning has been used for more than four minutes. The airflow from the heater fan will help to dry the housing and prevent mould growth. This module will adapt to other vehicles, or you can simply operate the fan for a few minutes with the a/c turned off to help dry the housing.
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