Wednesday, October 22, 2008

How Often Should You Change Your Oil?

This question is one that you will get anywhere from 3,000 miles to never, just change the filter. The truth is you can never change your oil too often but you can sure not change it often enough. Common sense tells you that the more you do it, the better. But do you really want to be changing your oil every 1,000 miles, I sure don't. Manufactures of your vehicle will tell you every 10,000 miles or so. You buddy with an older classic car swears by every 3,000 miles. And Bubba tells you he has never changed his oil and just changes the filter. You know the story, oil does not wear out. The fact is that every time you start that engine  the normal combustion is producing lots of water, and some of it gets in your crank case. Even more if the engine is high mileage and worn. Large quantities of air are being drawn into the engine, as any high school student knows, air contains water and water is a horrible lubricant. If everything is working as it should with your crank case breather system, the vast majority of the moisture is removed. But it very cold weather a lot of condensation takes place. That water in your engine dissolves any nitrates formed during combustion. That creates Nitrous Acid which is circulating throughout your engine. Nitrous Acid in your engine is a very bad thing. Knowing this, how often should you change your oil. That answer is determined by a number of factors. Of all the factors involved, miles driven is the least important in most cases. Those factors are:
1. Number of cold starts
2. Average Outside Temperature
3. Condition of the engine
4. Total Distance Traveled
So what is the answer. Well, I really have no definitive answer. I have no idea how you drive,number of cold starts,  the average temperature where you live, mileage you drive each year, nor the condition of your vehicle. I simply cannot tell you what is right for your car. I live in the south with mild winters, drive around 9,000 miles a year, mostly highway, with not a lot of cold starts. I change my oil and filter every 5,000 miles. I use conventional Pennzoil oil and a quality Purolator filter. I also change my Air Filter every 30,000 miles and do not drive in dusty conditions. For my situation this seems a good compromise between changing it every 1,000 miles and every 10,000 miles as my owner's manual states. Remember that every time you drain the oil pan you are draining away all the fine particles suspended in the oil. Remember also to never ever overfill the crankcase. Check the oil level with the vehicle sitting on a level surface after the engine has been shut down for at least 30 minutes. The problem with overfilling an engine is that as the crankshaft turns it create pressure. An over full engine will develop enough pressure to blow out the rear main seal. That leaking oil will ruin the clutch on a manual transmission equipped vehicle. Then later on the front main seal will let go. The crankshaft will dip into the oil and create a froth mix. This froth is a mix of oil and air. Air is a poor lubricant. The bearings will take a real beating from lack of lubrication. Too much oil is just as bad as too little. Bottom line is make sure you check the oil level correctly before adding any more oil.  

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Mayfield, Ky, United States
Retired and have been working on automobiles for over 50 years. I have learned that the best way to care for your car is to DIY. I personally do not trust the kid working at Spiffy Lube to change my oil. If, I want it done right I do it myself. Automobiles today are very complex but some things you can still do yourself. I have years of experience working on all kinds of vehicles and want to pass along what I have learned to those wishing to DIY.