Tuesday, March 25, 2014

Control Your Cruise


Modern cars go much further in preventing driver fatigue than the cars from years past. Anything the engineers can do to make the car more pleasant to drive is a good thing. One feature that does this very well but that has actually been around for a very long time is cruise control. This feature is not new but it has evolved tremendously and really doesn’t function at all like it used to.

The first cruise control systems used canister with a rubber diaphragm attached to a cable that would hold the throttle open when engine vacuum was applied to one side of the diaphragm. When the driver wanted to increase the set speed a vacuum solenoid would allow more vacuum in to act on the diaphragm. When the driver would hit the brake a valve attached to the brake pedal would let all the vacuum out and the throttle would snap shut.

Newer systems started using more electronic controls such as a small electric solenoid that could pull on a cable to hold the throttle open at the set speed. These systems looked at vehicle speed sensors to make sure they were accurately maintaining the set speed. A change in the set speed caused the electric solenoid to pull the throttle open more or allow it to close. When the driver hit the brake pedal an electronic switch would signal the actuator to release the throttle.

Electronic throttle control makes cruise control simpler.
Every car today whether it has cruise control or not is equipped with electronic throttle controls. The gas pedal is no longer attached to a cable that goes through the firewall to pull the throttle open. The gas pedal is attached to a sensor that tells a computer the driver wants more throttle. The computer then commands an electronic motor to open the throttle the requested amount.

Since there is a computer controlled actuator working the throttle, the only thing we need now to make cruise control work is a switch that tells the computer to hold the throttle open even when there is no foot on the gas. So the sensor attached to the gas pedal, and the buttons for the cruise control signal the same computer. This is a good example of computers simplifying the systems under the hood. A cruise control actuator and all the associated linkages are no longer needed.

This is not where the evolution of cruise control ends. Many cars are also now equipped with what is known as adaptive cruise control. This will not only hold the vehicle at a set speed but it will also reduce speed as needed to keep from getting too close to the vehicles in front of you that are traveling more slowly. The driver not only sets the cruising speed but they can also set the minimum following distance.

At the front of the car there is a sensor that uses lasers that bounce off the car in front of you to measure the distance between you and them. The computer will reduce the cruising speed as needed so you don’t get too close and once the car in front of you moves or speeds up the car will go back to the set cruising speed.

Adaptive cruise control won't let you get too close to the a slower car.
Adaptive cruise control is certainly one of those features that may cause us shake our heads in regards to the many new and somewhat silly features that we find on cars today, but of course this is where we are. In many ways these features that seem silly can actually make the car safer to drive by reducing driver fatigue and distraction. So while it seems that cruise control is the same as it ever was, it turns out it isn’t.  

Thursday, March 20, 2014

Deceptive Lights: Check Engine Light


Everyone out there has probably had a car that had a check engine light come on at some point. Some of you might have even had one blink at you furiously. Sometimes, the illumination corresponds perfectly with the engine running rough, fuel economy falling into the basement, or the transmission shifting funny. Sometimes nothing seems different in the way the vehicle runs at all. Either way, anytime the light illuminates it means something is broken. However, when the check engine light illuminates, it probably doesn’t have anything to do with the engine itself. This can make the check engine light deceptive.

This little light of frustration and angst will illuminate anytime the engine control computer sees a failure in the powertrain controls that will cause an increase in vehicle emissions greater than 150% of the federal test standard. This means if something breaks and it causes your car to potentially pollute more than normal, the computer will turn the light on. Most of the time this failure is electronic in nature, and not mechanical.

The check engine light varies somewhat from one vehicle to another. Federal law dictates what it can be, but there are several options. The light must be amber (yellow-ish) in color. The light may say “Check Engine” or it might say “Service Engine Soon.” It may appear as a silhouette of an engine alone, or it make appear as a silhouette of an engine with the word “check” or a strange lightning bolt arrow in the middle.
Many old cars from the early days of computer controls may have used something completely different for the check engine light. On these old cars every manufacturer could do whatever they wanted when it came to this malfunction indicator lamp. Honestly, most cars back then were not smart enough to illuminate whatever they used for a check engine light when the vehicle experienced most failures, so the check engine light was not a very useful thing.

Federal laws regulating exactly what the check engine light should look like and exactly when and how it should illuminate didn’t become standardized until the 1996 model year. These new standards which are still in use today are known as OBDII. These standards came about to make things such as check engine lights simpler for vehicle drivers to understand, and to make the problems for which they illuminate easier for technicians to diagnose.

The most common failures that cause the check engine light to illuminate relate to the engine not running right at its most efficient. This inefficiency can cause rough running, stumbling, hesitation, lack of power, poor fuel economy, and of course increased emissions. Sometimes the engine will not seem to run any differently than normal, but this is not always perceptible to the driver, so if the light comes on it must be diagnosed.
Many times you will take your car into the shop to have the check engine light diagnosed and the technician may not be able to figure anything out right at that moment. Rather than educate you on the situation and the nuance of intermittent problem diagnosis, they may leave you with the impression that nothing is really wrong and sometimes lights like this just come and go. This is never true. If the light is really coming on for no reason it's because something is broken. If the light is coming on for a reason then something is broken. No matter how you slice it something is wrong. 
A scan tool that can be used to read diagnostic trouble
codes that caused the check engine light to come on.

Diagnosing an intermittent failure that causes the check engine light to illuminate can be difficult and can take time. Be patient with your mechanic and understand that the time they spend working on this issue should not some free. Their time is their livelihood and you must pay for it even if it seems as if progress comes slowly. You would be patient with a doctor trying to figure out a physical ailment so you ought to show the same patience with your mechanic, after all, he can't ask your car where it hurts.

The check engine light must also not be confused with service monitors. Many vehicles have systems that can monitor the time and mileage intervals that elapse between vehicle services such as oil changes and tire rotations. Some of these monitors are very sophisticated, and some of them simply count the miles for you. A service indicator might say something such as “Service Vehicle Soon” or you might see a small illuminated wrench. To make things more confusing the vehicle that uses the service vehicle soon indicator might also have a check engine light that says service engine soon. These are totally different but can be really confusing if your vehicle has both of them.

Consult the owner’s manual for a proper explanation of the maintenance monitors and the associated indicators. The manual will tell you how they work, and it will even tell you how to reset them most of the time. The check engine light on the other hand has no simple reset procedure. If it comes on, something must be repaired.

The one thing that is usually certain is that the illumination of the check engine light has nothing to do with the engine itself. Some people worry about the pistons and valves and other mechanical components of the engine when this light comes on, but most of the time these things are fine…most of the time. 

Sunday, March 2, 2014

Monitoring the Thermostat


This is not that control panel on the wall of your house that you argue with your significant other over where the ideal setting should be. The thermostat is a control valve within the cooling system of your engine. Like the control panel for the furnace in your house, the engine thermostat is used to regulate temperature.

When the engine is cold the thermostat is closed, so coolant flow is restricted. This allows the coolant to heat up much more quickly because it cannot make its way out to the radiator where heat is released from the coolant into the outside air. The thermostat is located at the coolant outlet pipe coming from the engine going to the radiator.

Normal engine operating temperature is about 190 to 200 degrees F. Once the engine gets to a temperature close to this, the thermostat will open automatically. Most thermostats contain some kind of device that expands and contracts with temperature. When this thermally reactive unit gets hot it pulls the valve open allowing coolant to flow.

There are no fancy computer controls at work here, just old fashioned thermal expansion causing this thing to open. When the coolant gives off enough heat in the radiator to start bringing down engine temperature, the thermostat will react by closing slightly until the engine temperature is maintained at the optimum level for which it was designed.

Two problems result from a thermostat that has malfunctioned, but only one of them is well known because it leads to massive engine failure. The first and most dramatic thing that could happen when a thermostat goes bad is overheating. A bad thermostat can cause this when it simply fails to open at the proper temperature, or it gets stuck while opening and fails to open all the way.

When the engine overheats, the coolant heats up way past 190° to a point where the expansion of the various metal parts of the engine cause the parts themselves to fail. An engine can run safely up to about 230° F with no problems. When the temperature gets much above that the coolant can boil. Once the coolant boils it will build very high pressure in the cooling system and will boil over past the radiator cap or through the coolant expansion tank. This is why you see steam coming from some cars broken down by the side of the road. If temperatures get up to about 250° F the possibility for engine damage becomes a reality. Parts get weak and cylinder pressures go through the roof, literally.

The other thermostat failure that is not as well known but is probably just as common is overcooling. This is of course the opposite of overheating. Instead of the thermostat being stuck closed, overcooling happens when the thermostat is stuck open. If the engine is not allowed to warm up with the thermostat blocking coolant flow, it might not reach operating temperature at all.

Overcooling does not lead to a dramatic meltdown of expensive engine parts, which is why it goes undetected so much of the time, but it is still a problem that should be fixed. When an engine does not reach operating temperature it will not be able to maintain the correct air/fuel ratio. It will run rich, or with too much fuel. This is going to have an impact on fuel economy, but it will also have an impact on how much power the engine produces, and how much pollution will come from the tailpipe.
A typical engine that suffers from a thermostat that is stuck open might run as cold as 140° F. This might not seem that cold but it is. At this temperature you likely will not see your engine temperature gauge move very high off the lowest readings. In addition to this your heater performance will most certainly suffer. On those cold days when ambient temperatures are below 0, your engine will never come close to heating up, and you will probably have frost develop on the inside of the windshield.

Diagnosing a bad thermostat is no problem for an experienced technician. Many times a good repair shop will also recommend thermostat replacement anytime any work is done on the engine near the thermostat, regardless of whether or not it is currently known to be bad. Thermostats commonly go bad at inconvenient times, and considering it’s a $10 part, you should have it replaced anytime your mechanic is in the area.

Keeping the thermostat working will keep your engine running better, keep your fuel economy and power output up. And keep you from suffering a major breakdown from overheating in the middle of nowhere. Don’t forget about your thermostat, it would be a shame for a $10 part to cause so much grief.