Why Changing Your Oil Is Important and How Often You Should Change It


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From Ross:

An oil change is often one of the first jobs a tenderfoot will undertake on a prized automobile, and it is worthwhile to early establish habits of safety, prudence and the necessity of doing the job correctly that these habits will continue over to the difficult ones whence an accident may prove disastrous:

One should check the Chrysler Chassis Manual of the appropriate year, perhaps a good aftermarket one, for the value assigned to "tightening the oil pan drain plug". And, yes, owning the chassis manual and a torque wrench of an accurate type (click over beam; direct read best of all) ought to be stressed to the newcomer. Use of a proper gasket, nylon or dead soft copper, along with some medium-strength Loctite, is also a good idea.

Jack-stands are great, but not always necessary, some vehicles one only needs extra-long arms. Plus, the rear wheels should be chocked, the emergency brake down to full extension any time one is under car for any reason. Jack-stands should, as a matter of safety, support at least 6-tons. Sears has all of the above tools, and at reasonably cheap prices compared to professional tool distributors.

Also, an inexpensive rolling floor jack to raise the car (change hydraulic fluid annually) instead of the bumper jack which is pretty much an emergency-use-only tool.

Oil changes may be done when hot or cold. Key is adequate drain time: pan should have fifteen minutes minimum to get all of the old, very-slow draining contaminants a chance to creep out (why I prefer having let the car sit overnight in the position at which it will be serviced). They don't call it "sludge" for nothing.

While oil is draining, this is a good time to use a rag to clean off and inspect steering and suspension components; just have a good look around. Sniff the oil to notice any particular odors: gasoline, harsh acridity, etc. Lubricate the new filter's "rubber" gasket with USED engine oil, thoroughly.

Try to find an oil funnel which will support itself when wedged slightly into oil filler. Keep it wiped clean and in a plastic storage bag unless one wishes to add contaminants at change.

Oil dipsticks are notoriously inaccurate. Having drained an engine with sufficient time allotted, when one has added the correct amount of replacement oil and new filter, run the car long enough to establish operating pressure, shut it off. Check level very closely on dipstick, and, if necessary, mark the dipstick by drilling a tiny hole at that point or using a tool to mark a new line; both for the FULL and ADD marks.

It is not unusual to have minor consumption the first few hundred miles as some chemicals boil off. I like to add oil whenever the sump is down by a half-quart, and record the mileage until, all things otherwise, I am familiar with the engine's rate of consumption or loss by leakage. Both indicate the need for repairs at some point. An engine in excellent condition will use a half-quart or less of motor oil under "regular" conditions of service, a bit more under severe but not to exceed one-and-a-half quarts in 3000 miles.

From Dick:

As some of you know, I have a very large number of collector cars, therefore some of them sit for years without being driven. I wish I had a better way to rotate them, but the way I have them packed into my storage buildings, it is just too much trouble to dig out a different car everyday, so often I concentrate on 3 or 4 of them and let the rest sit. 

Oil needs to be changed for these reasons:

1. buildup of corrosive byproducts of combustion which could erode metal parts left to soak in it (pull a dipstick of any car that has seen long storage and note how much erosion has occurred on the portion of the dipstick that was below the surface of the oil - you may be amazed!), and 

2. breakdown of additives and lubricity due to heat and mechanical stress on the oil, and 

3. accumulation of dirt in the oil from debris caused by blow-by (carbonized oil and fuel), and 

4. contamination cause by fuel or coolant leakage. Only the last reason is operative for a car which is not being used. This will occur only if there is a problem with the carburetor leaking fuel, or the cooling system gaskets or porosity. 

If neither of these problems are suspect on a car, I see no reason to change the oil on a car which is not being driven. I know of no deterioration that occurs to oil just from sitting, at least not with modern oil. Therefore, with my older cars, which do not have the very best of oil filtration system (Packard never did adopt a full flow filter), I think the oil should be changed every 1500 miles of actual driving, and I put no time limit on that. On the newer cars, with modern spin-on full flow oil filters, I'm sure it does no damage to run at least 3000 Miles between changes. Always change the oil before storing the car, though, if it has been driven more than a few hundred miles since the last change, to avoid the corrosion problem.

This page last updated October 24, 2001.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club