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The cylinder head gasket is probably one of the most important sealing components in the engine. One of the telltale signs when this gasket fails is that coolant will mix with the engine oil. When this happens the engine oil will turn to a milky color and a jelly like consistency. Often the more severe the leak the milkier the oil becomes.
Picture of head bolt tightening procedure
Head Bolt Tightening Pattern

One of the biggest causes of repeat repairs when a head gasket is replaced would be the procedure for tightening down the bolts was not followed correctly. Head bolts must be tightened in the correct order and to the proper amount of torque. Tightening sequences and specifications are available in your car service manual that will also include the step by step repair procedure for your model.

Most cylinder heads are tightened in a sequence that starts in the middle and then moves out towards the ends. The bolts are generally tightened in two or three stages. If the final torque is 100 foot-pounds the bolt may first be tightened to 50 foot pounds all away around before the final specification is reached.
 
 
The check engine light is turned on when an engine misfire is detected because unburned fuel pouring into the exhaust manifold will cause extremely high tailpipe emissions. Also if the situation continues raw fuel entering the catalytic converter can cause internal damage to the catalyst.

This will also increase tailpipe emissions and will most likely lead to having to replace the catalytic converter which happens to be a very expensive part on most vehicles. For this reason computers can be very sensitive to engine misfires and illuminate the check engine light even if the problem is intermittent.

Misfire monitors

Picture of crankshaft sensor
Crankshaft Sensor
The onboard computer is capable of quite complicated misfire monitoring. The engine control module uses the crankshaft angle measurement to detect this misfire. It's actually quite amazing how it is performed. Click the read more button to see how it works.
 
 
Power sunroof problems reviewed. Many malfunctions in the sunroof system fall into 2 categories that can often be related to each-other. Water leak issues and electrical problems. Sometimes wiring or switch corrosion can be caused by the water leaks.
Picture of power sunroof
power sunroof

A power sunroof can slide the roof panel open or closed. You can also tilt the roof panel up in the back to allow fresh air into the passenger compartment. When driving down the road this can also pull a vacuum and remove stale air from the interior cabin.

In most cases power sunroofs are not that much different than electrically operated power window systems found in most automobiles. Many common parts are shared such as system relays, a master control switch and the motor assembly to perform the movement.

Note that most power sunroof systems are protected by a circuit breaker instead of a fuse. This is in case the sunroof begins to bind. It protects the motor by opening the circuit breaker. Often when people have power sunroof problems they will begin to look for the fuse when there is actually none. A circuit breaker will reset automatically when it cools down.
 
 
Repairing car power seat problems can sometimes be as simple as removing a penny from the seat track. Or they can be as complicated as having to test switches, relays and motors. Most power seats are not protected by a fuse but instead use a circuit breaker.
Picture of power seat switch
power seat switch

Before we get into what to look for when your power seat is not working let's talk about why this issue is more common.

Vehicles that are equipped with a power seat option are becoming much more common than they were just a few years ago. Where as they use to be exclusively deployed on luxury cars you can now find this popular option on even the most basic models.
 
 
A common complaint from drivers and motorists would be car vibrations occurring at highway speeds. Most mechanics and myself included would first concentrate on tire problems and wheel balance.
Picture of driveshaft universal joint
driveshaft universal joint

And this is definitely the most common cause of vibration complaints. But what do you do when you put on new tires and they balance out perfectly yet the vibration continues to exist on the vehicle. If the car is a front wheel drive automobile checking out the CV joints and the drive axles would seem to be the next logical step.

If it is a rear wheel drive automobile universal joints and drive shafts should be inspected for problems. Often these different types of driveshaft components can create car vibrations that feel very much like tire balance issues.
 
 
Dirty fuel injectors have become a big selling point for popular fuel additives and gas companies. A few gas companies say that they add chemicals to their fuel that will help keep your injectors clean and make your engine run better.
Picture of fuel injection cleaning kit
Fuel Injection Cleaning Kit

Some companies selling fuel injector cleaners state that they will increase fuel economy and restore engine power. All of the above statements may be true if you actually have dirty fuel injectors.

Before you pay more at the pump for gas or go out and purchase additives and cleaning solutions it would be nice to determine if they are actually needed.

Testing the flow rate and the efficiency of the injectors can not only be performed but can verify whether cleaning is necessary. I have more information on fuel injector testing on my you fix cars website.
 
 
Lets talk about testing automotive AC. Although it is still winter our thoughts will soon be thinking of spring and summer. It is a common condition that after a long winter season of not using your automotive air conditioning it may not seem to operate correctly when you do turn it on that first warm day.
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ac test guages

Testing automotive AC can be tackled in the driveway by a DIY car mechanic with some experience wearing comfortable safety glasses. Performance testing the system is a good place to start.

Performance testing provides a measurement of air-conditioning system operation and efficiency. It is recommended that a manifold pressure gauge be used to determine both the high and low pressures in the automotive AC system.

These manifold gauge sets have really come down in price over the last few years. Although professional grade sets can cost well over $100 a good DIY set can be had for fewer than 50.

This could be considered a good investment that will return big rewards over time on several different vehicles.

Automotive AC pressure readings

The desired pressure readings will vary according to the temperature during the time of testing.
 
 
When it comes to automobile repairs. The word diagnosis is thrown around quite a bit by both the professional technicians and driveway mechanics. Diagnosis is the opposite of guessing at what is wrong.
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Online auto mechanic
When customers need their cars repaired, or if they are going to attempt the repairs themselves proper automotive diagnosis can help control costs, as well as produce reliable car repairs.

The more the driver understands the problem with their vehicle, the better the communication will be with the mechanic or auto repair shop.

And this communication can be critical for diagnostic charges. If the mechanic is looking for something different than your complaint much time can be wasted.

So to follow is some recommendations about understanding your individual car problem and taking it to the next level by actually doing some research before any action is taken.

Diagnosing automobiles

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code diagrams
To properly diagnose car problems it is best to follow a series of interrelated steps in order to find the solution to a specific car problem.

Automotive diagnostics is a way of looking at a system not functioning properly and finding out why.

This is achieved with a thorough understanding of how the system that is malfunctioning, operates when in perfect working order.

 Example, if you're car doesn't start and you believe that it is the fuel pump causing this condition. The first step is to sit down and understand the operation of the fuel pump circuit.
 
 
With fall here and winter approaching car heating problems can become just as important as air conditioning in the summer months.

No driver wants to freeze or burn while they're driving their car down the road.
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heater control valve
The heater control valve is one of the many components that are responsible for warming the interior compartment. This valve allows hot coolant to be piped directly from the engine to the heater core.

The heater core then transfers the heat to the interior compartment by recirculating air from inside the car across the heater core fins.

This continued cycle of heating the air inside the vehicle is extremely efficient.

Heater control problems

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climate control
Many things can cause low output from your car's heater. Understanding how to heater control valve works can be important in diagnosis of this car problem. The heater valve sometimes called the water flow valve controls the direction and amount of coolant flow to the core.

In the closed position to heater control valve allows no hot coolant to enter the heater core. In the open position the part allows engine heated coolant to circulate through the firewall mounted core.

Consult your online auto service manual for specific locations on your vehicle.
 
 
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Check Engine
The oxygen sensor is often suspected when the check engine light comes on. The O2 is one of the most commonly replaced sensors.

It is also one of the most misdiagnosed, electrical emissions components. Since this sometimes-expensive car part is a non-re-terminable item at most part stores, it is a good idea to confirm diagnosis before replacement.

And often during my diagnostic procedure I will uncover the cause of the check engine light problem that is less expensive then a replacement o2.
Add to the above facts that most cars have 4 of these exhaust stream sensors and you really want to make sure you are only replacing failed components.

To follow is a run down on how to diagnose check engine light codes in the PO171-PO175 range, which are your most common o2 codes.

How to Diagnose oxygen sensors

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Cheap Scanner
To effectively diagnose failed oxygen sensors you need to see the operating voltages. A scan tool is the easiest way to do this but an automotive meter can also be used. Diy scan tools that can read data streams can be had for under $200

The data stream voltage for the O2 should vary quickly from about 200 to 800 mV. A good rule of thumb is that the voltage should vary above and below the half way mark of 500 milivolts in a steady even pattern.

If you have sensors with a fixed voltage or a voltage that is always below 500, then you want to check the wiring to the sensor.