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How Often Should I Change My Oil?
This is one of those questions that, if you ask 10 different people, you get 10 different answers. Here's my take on the subject.
First of all, you should have an understanding of why you should change your oil. Oil's main property is to lubricate your engine's internal parts. Unfortunately, your engine runs on the combustion of gasoline, (or diesel), and this burning of fuel produces by-products like carbon and other such chemicals. These by-products are absorbed by the engine oil causing it to get "dirty". This is why you have an oil filter. The oil filter cleans the oil that is pumped through it, but only to a certain degree. It more-or-less picks up the bigger particles, down to 4 microns, but will let the smaller particles pass through. (Think about it, if it picked up all the particles it would plug up quickly and no oil would pass through!). So the rest of the particles are left in the oil. For this reason, oil has additives in it, to suspend the particles and not let them settle into the engine, similar to how fruit is suspended in a bowl of Jell-O. This way, when you change your oil, almost all the contaminates are removed with the oil.
So now that we know why to change the oil, all we have to do is figure out when to change the oil.
Oil has a saturation point. It can only hold so much stuff, like a sponge can only hold so much water. When it reaches this point, the particles will start "falling" out of the oil and settle in the engine somewhere. This is called sludge. Also, over time, the additives will start to break down and the oil will lose some of it's suspension qualities and make matters worse!
So the best time to change the oil would be just before it's saturated and the additives are still working.
Most car manufactures will have a recommended oil change interval of around 7,500 miles. Some are as high as 15,000 miles using synthetic oil. (A whole other subject). This is fine, but you have to understand how they set these standards. First of all, the manufactures have yearly maintenance cost posted on every car they sell and, of course, they want to keep these numbers as low as possible to appeal to the buying customer. Secondly, they are calculated under ideal driving conditions, something few of us are able to attain. If you live in Hawaii, where the temperature is between 78 and 84 degrees all the time and you drive nothing but highway miles, everything would be good. But we live in Wisconsin, where the temperatures can fluctuate from -30 to over 100 degrees, and few of us drive just highway miles.
Cars don't like to run cold. I'm sure we all cringe a little when it's 15 below zero and we have to go out an start our cars! They moan and groan or shudder a little bit but they soon smooth out and run fine (sometimes). The fact of the matter is, engines are designed to run with a 200 degree coolant temperature; this is where they are most efficient. Starting one cold requires a lot more fuel an a higher idle. This is why your gas mileage goes down the tubes in the winter. A lot more fuel makes a lot more carbon and other particles, and that gets absorbed in the oil.
Your owner's manual will have two maintenance schedules in it, normal and severe. We definitely are not normal (I mean Wisconsin weather, not us!), which is what the oil change mileage is based on, but I don't think we are severe either. There has to be a balance and everyone drives different.
Here's my final conclusion. I have never seen an engine failure due to someone changing their oil too much, but I have seen engine failures from changing oil to little. A vehicle is the second largest investment people will make next to their home (the average car costs $18,055.00). why take the risk over a $25.00 oil change? I cannot tell you exactly when your oil reaches the point when it should be changed, there are too many variables, but I do think changing it every 7,500 miles is too long, I have seen it first hand over my long career.
My recommendation is every 3,500 miles or twice a year. (fall and spring). If you do mostly highway driving, you can stretch this a little, but here is my final point. The average person puts on 12,000 miles a year. That would be four(4) oil changes or about $100.00 annually. considering a modern day engine replacement could cost $5,000.00 or more. I think it's cheap insurance to make sure your oil never reaches the breaking point; and to protect your investment.
American Imports Inc.
N96 W14433 County Line Rd.
Menomonee Falls, WI 53051
Hours: M - F 7:30 am - 6 pm