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Old 11-01-2000, 07:39 AM
420SEL 420SEL is offline
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Join Date: Jul 2000
Location: Toronto, CANADA
Posts: 1,193
As Larry said, there are other factors involved with the deterioration of your engine oil besides mileage. All engine oils contain detergents and additives. These additives allow the oil to withstand fluctuations in temperature and also to suspend the byproducts of internal combustion. These aditives will wear out more quickly if they are exposed to extreme operating conditions (such as towing a trailer across country) etc. They will also simply wear out over time. As Larry said, if you are using Mobil 1, given your stated use, you should change it every 6 months at least. It is cheap insurance. If you are using regular oil change it every 3 months. There is something else to consider. That is your driving style. 7,500 miles a year works out to about 37.5 miles per day if you only drive your car on week days. Assuming you take one or two long trips a year this leads me to believe that most of your driving is short trips (15 miles or so). Short trips do not allow your engine oil to heat up fully. Even if your engine temp indicator has reached its operating level by the end of your trip your oil may not have heated enough. This is significant for several reasons. As I mentioned before, when you drive there are byproducts of the internal combustion process. Most of these contaminents are very acidic. These contaminents are suspended in your engine oil and will burn off if the oil gets hot enough. If your oil does not get hot enough they will remain suspended in your your engine oil and can do damage over the long term. Condenstaion can be another problem. When the weather gets colder your engine starts off cold and heats as you drive. This causes condensation. This is not a problem if you drive long enough to burn the condensation off. If your engine doesn't get hot enough it will not burn off the condensation and that will remain in the oil. This can also cause problems over the long term. Condensation can leave a white film over some of the hoses that oil passes through when the engine is running. When the engine stops this forms into a goo, and it can seriously prevent proper oil flow. It happened to me once so bad that when I started the car I was getting no oil pressure. The Breather hoses had been full ove condensation which had frozen over night on a trip to Quebec. The oil couldn't pass through the breather hoses and was blowing right out of the dipstick. Fortunately I always try to keep an eye on the guages and shut the car off immediately when I noticed no pressure. I lost about 4 quarts through the dip stick. I had to remove the breather hoses and clean them thouroughly as well as the valve covers. They were full of white gunk. Fortunately no damage was done. Needless to say I now change my oil every two months or 2000 miles, which ever comes first. At alittle over a buck a quart for Castrol GTX it is indeed cheap insurance. Change your oil more than once a year. If you follow the FFS and change every 10,000, at the rate you drive than is one oil change every 1 year and 4 months. That really should be almost three changes if you use Mobil 1 and at least 5 if you use regular oil.

Jason Priest
1986 420SEL
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