Why should you change your oil frequently? The best answer is, to keep your engine young and healthy. Your engine undergoes a lot of stress through many temperature changes. Metal and rubber react to these changes in many ways. Warping, cracks and the rubber seals really take a beating. You may get ridiculed for changing your oil every 3000 to 5000 miles. However, after 300,000 miles down the road, see who is laughing then.
There are many benefits of keeping your oil changed, with clean, fresh new oil. I say this because there are those that like to reuse their old motor oil. Never reuse old oils. For all the reasons to keep new oil in your engine, is why you don’t use old oils. Some think the life of the engine is in the changing the filter, but is it?
Why The Filter Isn’t The Life Of The Engine
Some think, that if you just keep the oil filter changed, you’re keeping the engine clean. This isn’t the case, the filter needs to be changed but that alone will not help. It is the oil that breaks down that actually starts doing damage to the engine. To help you understand why old oil can damage your engine, here is a quick overview.
Over time, the oil in your engine begins to combine with combustion gases. These gases are what seep by the piston rings and get trapped in the oil. However, this is by design, this is one of the oil’s process. As more of these combustion gases get trapped and built up inside the oil, it starts making the oil acidic. Specifically, it creates sulfuric and carbonic acids.
These acids eat away at all the metal parts and rubber seals in an engine. This causes the seals and gaskets to get hardened. Seals lose their flexibility, become malleable and lose its anaerobic qualities. These chemical changes allow oxygen to work its way into the seals and gaskets causing erosion and decay. The engine will start leaking oil. Metals that the oil is supposed to protect, will start breaking down. This will allow the metal on metal friction to increase, thus the lubrication decrease.
Oil is Oil Right?
There are those that think that oil is oil and it will last forever. They feel that the 10W30 bought two years ago, will still be 10W30. This is very wrong thinking, that oil is nothing but black acid, and killing your engine. Of course, I have already got into why oil over time breaks down over time. But oils are not all the same and do change with use.
They make many different types of oils, and some have specific applications. When it comes to your car engine, you have choices in brands and quality. However, it is recommended to stay with the type and weight specified by the manufacturer. You can use conventional, synthetic blend or full synthetic. Synthetic oil is much better than conventional oil but synthetic oils were designed for 
newer car engines. Conventional oils were basic crude, that was run through some refining processes. A synthetic blend is a mixture of both full synthetic and conventional.
Conventional oils today are made more synthetic than most people realize. It is still processed more from crude oil, however, it has many chemicals added to it. The difference between conventional and synthetic is the ability to maintain viscosity. Conventional oil starts breaking down when it gets heated. So, if you started at 30W, ran an engine for an hour, it will potentially drop to 10W. Hence, the 10W30 label on an oil bottle. Manufacturers make oils at a certain weight and have tested it to see what weight it drops to when hot.
Looking At Synthetic and Conventional
Synthetic oils hold up against heat far better, and keeps its higher weight rating longer periods. Additives are mixed in with derivatives of crude oil to create a synthetic oil. Internal parts of an engine get coated with these additives from the synthetic oils reducing friction. Conventional oil doesn’t work quite that way. It is more of a lubricant that reduces friction as long as it is in contact.
Engines today are built with tighter clearances and require better oils. Synthetic oils can flow up to seven times faster than conventional oils. Engines with tighter clearances really need thinner oils. This is why you see engines use 5W20 or even 0W5 oils today. With synthetic oil, you get a higher flow rate. Oil is getting to the job faster and this is particularly important when we talk oil viscosity per temperature.
As you can see, oil isn’t just oil. The newer engines require synthetic oil due to is viscosity. I haven’t even talked about transmissions, gear boxes or differentials. All of these components require specific types of oils. If you were to use the wrong type of oils in any of these, you could be looking at its destruction.
So What Good is Conventional Oil?
When I first got into cars and motorcycles, my dad taught me that in the summer, you run 10W40. In the winter you run 10W30. You ran thicker oils in hot weather and thinner oils in colder. This is still basically true, more for older cars. So it does sound a little like a hassle to run a conventional oil. Especially following the weight change between seasons. However, conventional oils have a purpose.
Conventional oils are made much better now. Although, conventional is inferior with temperature change compared to synthetic oils, they have a purpose. As I mentioned earlier, a synthetic oil applies a coating to engine parts. Conventional oil only lubricates while it is in contact with the parts, so it doesn’t coat. This is really important on a brand new engine. There is a statement floating around out there that is totally wrong. “Whatever oil you start your engine off on is what you should always run in it.”
Conventional Is Good For Rebuilt/New Engines
I have rebuilt more engines that I can remember. I can tell you, never break a new engine in with synthetic oils. As I said, synthetic coats engine parts, which means it coat the piston rings. When an engine first starts up for the very first time. The piston rings have to cut there way in the cylinders. If there is a coating that resist this friction, the rings will never seat. This also applies to the camshaft and lifters. The flat tappet lifters and cam lobes have to a have seating process, unless it is roller lifters. It is important to break an engine in with conventional oil.
I usually run an engine about 1500 miles before changing the oil and filter. Conventional oil will be ran for the second oil change as well. 2000 miles will be ran before I switch over to synthetic. Factory engines usually go through a break in process before the consumer buys the vehicle. A machine helps pre-seat the rings and cam. So if you started your brand new car out on synthetic oil, you shouldn’t have any issues.
Some Engines Work Better With Conventional
Conventional oil’s slower flow, is better for older and aging engines. Synthetic oil flows faster, kind of like it was thinner than regular oil. Older or aging engines have more tolerances in between engine parts. The longer they run, the looser they get. So if your oil is kind of thin and flows by quickly, there isn’t much to keep it lubed. Old car lot trick, when an engine is knocking, you pour really thick oil in it to quite it down. Same principle applies here.
There are also certain type designs of engines that won’t work well or at all with synthetics. As engine designs are becoming more advanced, most newer engines will work with synthetics. However, a little older engines, like vertical shaft lawnmower engines work best with conventional. These engines use aluminum piston rods. These rods run straight on the crank with no bearing. So the thicker, slower viscosity oil lubes better, plus helps with the looser tolerances.
There are “Opposing” engine designs many some manufactures make. Example for old Volks Wagons, Subaru and more. This means that the pistons are lying flat on their side. For every piston, there is one on the opposite side of the motor. All the pistons pull into the center and push outward at the same time. Thus, calling its design, “Opposing”. Due to the design of this engine, the way the oil pumps were made originally, conventional oils worked the best.
Thin oils, or fast flowing oils would go right through the rings and the engine would smoke. The design got better over time and thinner oils can now be used. However, this shows that conventional oils do work better in older engines.
Reasons To Keep The Oil Fresh
My brother had a car that used oil. It would use a quart a week, especially when he would go a long time never changing the oil. He felt that adding oil every week kept the oil fresh. Now I am going to tell you what I told him to prove my point. Change your oil frequently and it won’t use oil as much. I changed his oil, and it went from a quart a week to one every month and a half. He found his car ran better as well, even better mileage.
Keep good oil in your engine and never use old motor oil. By never changing your oil or using old motor oil. You are not saving anything and killing your engine in the process. This applies to lawnmowers as well. They are actually worse about needing fresh oil. Most lawnmower engines are air cooled. They hit higher temperatures that break oils down faster. So take care of your mower as well.
On a side note, if you change your own oil, you may have a time resetting the “Change Oil” indicator. This is the light on the dashboard that pops on to indicate, it is time to change your oil. This indicator can often be a pain to turn off. The engine or computer doesn’t know that you changed the oil, you have to reset it. If you are not sure how, please visit my page, “How To Rest Change Oil Light“.
Recap
Always change your oil filter every oil change. You want to keep all the contaminants out of your engine the best you can. If you have a new engine that is already broke in, use a synthetic or synthetic blend oil. However, if you are keeping your oil changed regularly, a conventional oil is fine. Never use a synthetic oil in an old, aged engine. If it is already leaking or making noise, conventional works better in engines in this condition.
Research or ask a manufacturer what type of oils work best for your engine. Some designs of engines will work best on conventional oils. Many of the newer design engines were designed for synthetic. Remember, synthetic oils viscosity acts thinner and can get to parts faster. Synthetics coat the internal parts with a protectant, works great with engines with tighter tolerances. 
Conventional oils do not coat the internal parts. They only protect when in contact with the moving parts. Conventional oils viscosity acts thicker and moves slower. However works great for engines that are worn or have loose tolerances.
Never use old motor oil, keep your oil clean and fresh by changing your oil frequently. Think of oil in an engine like blood in our bodies. We have lungs that refresh and oxygenate our bloods. An engine doesn’t have this function, it relies on you to keep it fresh. So keep your oil changed to keep your engine young and healthy.
Please help keep our environment clean by taking your old used motor oils to the appropriate recycling and disposal locations. Advance Auto Parts and many other parts stores will take your old oils and batteries for free. Also your local community solid waste facilities usually has an oil tank for oil disposals.
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There is a whole lot on here that makes sense but that I didn’t know. Especially about synthetic oil as I grew up when it was not an option. Thanks for explaining it in a way I could under stand