Ask Joe Mechanic - How Important is an Oil Change?

It’s there dominating the “to do” list and procrastinating only makes it worse. It’s the car’s oil change. Was that reminder sticker on the windshield purposely put there to make you feel bad? Let’s try a different approach, looking at all the good things that happen when the oil and filter in your car are changed.

First lets assume your car is one that is driven a minimum number of miles and seldom reaches the 3,500 miles in three months’ time. Your vehicle needs the oil change more than cars that are driven more often. In the short trip mode the engine heat ups and then cools down for long periods creating condensation. The moisture can be seen accumulating on the oil fill cap in the form of a gray oily globular mess. Sometimes this condition can be misdiagnosed as an internal engine problem. You probably can drop back to an oil change three times a year or the minimum time interval prescribed in your owner’s manual. For normal usage, some people think cars can last 10,000 miles on their oil, others say not even half that. A nice general rule is every four to six months, or somewhere around 5,000 miles, especially if you are using synthetic or synthetic blend motor oils.

Secondly, oil breaks down over time and extended usage and it picks up dirt and contaminants, and these can deposit in your oil pan as a thick, gooey sludge which can eventually clog the pickup screen for the oil pump. If this occurs, it can cause oil starvation to the engine and cause a premature engine failure at worst, or at least the expensive cost of removing the oil pan to clean out the pan and the oil pickup.

Also, if your car has a turbocharger or a supercharger, regular oil changes are even more important. Remember the turbo is spinning at 100,000s of rpm.  It also runs really hot so any oil in the turbo when the engine is switched off will degrade unless it is in good condition. This also shows the importance of allowing the engine to cool down a little before shutting down after a spirited run.

Next, don’t underestimate the value of having a trained individual under the hood of your car. They will be able to spot a number of trouble situations that, if left untreated, have the potential to cause a breakdown. They should be looking for fluid leakage, cracked or frayed belts, bulging hoses and safety items including torn wiper blades, burned out lights, and unsafe tires. The success of this approach only works if you have found a shop that distinguishes true customer need from sales effort.

The regular oil change also establishes a benchmark of when your car’s maintenance needs are to be met. For instance, every third oil change can be the point at which the tires need to be rotated. Also, your recognition of what fluids had to be added may serve as the first warning sign that one of the systems is leaking. The need to repeatedly add coolant may indicate a leaking water pump, for example.

The underside of your car is rarely seen. The oil change provides the technician a chance to easily look for undercar problems. These would include torn CV boots, broken exhaust parts, or problems with the transmission or differential. Anything that’s broken, loose or excessively worn is in clear sight. This idea of the lube tech or service facility disclosing legitimate problems only works to your advantage if you’re in the hands of a reputable shop.

Your car’s oil change may be something you don’t look forward to and hate to take the time to get done. However, there isn’t a car maintenance procedure that is more beneficial to your car when it’s done by a service facility you trust.

            Just remember, your vehicle is likely the second most costly investment you will make in your life besides your home. If your sink is leaking or your furnace is due for service, are you going to ignore it? When water comes through your ceiling after a hard storm and you have a large wet spot on your ceiling, are you going to say, well, maybe next month I can get to it? I don’t think so! Treat your car the way you would your home and it will most likely give you years of good service.

Ask Joe Mechanic: Steering and Suspensions Part 3

The suspension of a vehicle serves a number of different purposes. The first and probably

most important is that it locates each wheel in relation to the others and provides a stable platform for steering and braking control of the vehicle. Additionally, it enables overall driving enjoyment and safety. The second purpose of a vehicle suspension is to isolate the passengers and cargo from bumps and irregularities in the road surface. Generally, these two requirements are at opposite ends of the suspension-tuning spectrum, so it requires a compromise that optimizes control without sacrificing comfort.

            The most important thing with any suspension is to keep the tire in constant contact with the road. Considering that each tire only has a few square inches in contact with the road surface at any given time, it is of utmost importance to maximize that contact. This is accomplished by using springs, shocks and linkages to properly locate each wheel. In many vehicles, there are different systems used at each end of the vehicle.

            If we had roads that were perfectly smooth, we would not need suspension systems. But as we all can attest to, our roads are far from smooth. If we did not have a suspension to absorb the bumps and jolts, the tires would never be able to stay in contact with the road surface. Newton’s first law states that for every action there is an equal and opposite reaction. This means that for every upward bump, this would launch the wheel upward with an equal force. For every pothole, the vehicle would first be forced downward and then upward as we exit the hole. 

            As stated earlier, the two most important factors are the ride and handling. These two things can be broken down into three determining factors, which must work together. The first factor is road isolation, which means finding a way to absorb the shock of road irregularities without causing undo motion or upsetting the stability of the vehicle. The second factor is road holding. This means a number of different things. It is regulating the transfer of motion from front to rear during acceleration or from rear to front during braking. It is also the transfer of weight from side-to-side to minimize weight transfer in order that the tires maintain a constant contact and friction patch with the road. The third factor is cornering. This means the ability to maintain directional stability and control weight transfer and road contact during changes in direction. This also includes controlling body roll. 

            To develop a working suspension system, which will control all these things and give us a ride quality that is acceptable for the type vehicle we have requires consideration and computation of quite a few factors. I have compiled a list of twenty-two factors, which must be considered in any suspension design for it to work properly. There could even be more factors to consider, but these are all definitely part of any design study. I plan to list each, along with a brief description of what each is. I won’t attempt to make you understand how each is determined, but give basic information to illustrate how complex this system can be to design, despite the finished product looking quite simple. 

            The first factor is spring rate. This factor determines the ride height of the vehicle and also the amount of force required to compress the suspension a set distance. When a spring is compressed or is extended, there is a force exerted that is proportional to the change.  The spring rate is determined by the change in the force it exerts divided by the change in defection of the spring. This is why a compact car has much smaller springs than a pickup truck. 

            The second factor is wheel rate. Basically, on an independent suspension vehicle, this is very similar to the spring rate. But on a vehicle with a solid axle such as a pickup truck, there are other factors that weigh in. When a solid-axled vehicle is cornering, there are different effects depending if it is accelerating or braking. For this reason, the springs are located as closely to the wheels as possible to limit the twisting motion.

            The third factor is extremely difficult to determine because it is affected by so many of the other considerations. This factor is known as the roll rate. Roll rate is influenced by the vehicle ride height, the center of gravity, the vehicle’s sprung weight, the track width, the spring and shock rates, the roll center heights front and rear, the stiffness of the anti-rollbars, and tire pressure and construction. The roll rate will often differ from front to rear to allow for turning ability and steady state handling. The roll rate does not change the amount of weight transfer in a vehicle; it actually controls the speed at which those changes occur. 

            We will continue this suspension system factors discussion in coming posts. Some information for this post obtained from www.wikipedia.org.