- Buyer's Guide
Dipstick oil analysis may sound a little goofy, but it works. Not to mention it’s also cheap and quick. There’s only one problem - figuring out what the oil on the dipstick really means. No worry. Sit tight for five easy lessons on reading your dipstick.
Lesson No. 1 - Retrieving the Dipstick
Lesson No. 2 - Detecting a Low Oil Level
Lesson No. 3 - What If the Oil Level is Too High?
Lesson No. 4 - Signs of an Aged Oil
Lesson No. 5 - Signs of Coolant Leak
So there you have it - dipstick oil analysis in five simple lessons. Checking your oil level may never be the same.
Have you learned tricks, not mentioned here, for using your dipstick to analyze used motor oil? If so, please share these ideas but beware, they might show up in print someday!
Is it OK to Be a Quart Low?
Automakers and owner’s manuals will often say it’s OK to wait until the oil level falls below the add mark to add oil. However, remember the crankcase of most passenger cars today holds only about four quarts of oil. This means you are running the engine with 25 percent less oil (one quart), which may not be wise.
Motor oil has many important functions beyond just controlling friction and wear. Oil not only lubricates the engine’s internal parts, but also helps cool the bearings and other frictional surfaces. The oil in the engine, therefore, serves as a heat sink to gather up unwanted heat to transfer it by conduction or convection out of the engine. Under typical driving conditions, running a quart low may not make much difference in terms of bearing temperature or overall engine lubrication. However, the engine also needs to be protected under worst-case conditions, such as in hot weather, while towing or with an impaired cooling system.
Likewise, when you’re 25 percent low on oil, you are also 25 percent low on critical additives - the additives that prolong the oil life and the engine. Additionally, when you are 25 percent low on oil there is less oil to disperse harmful contaminants, acids, soot, fuel, sludge and water that enter the crankcase. When you do the math, a quart low on oil translates to a 33 percent increase in contaminant concentration. Plus, the remaining oil spends less time at rest in the oil pan and more time in the hot frictional zones of the engines. The added heat, shear and pressure will more rapidly degrade the oil and its additives.
Once all of this is brought into the picture, especially the prospect of an extended oil change, for many car owners it’s a good idea to add oil whenever the dipstick reads low. Don’t wait until it is down a full quart. If it needs half a quart, add half a quart to bring it back up to the full mark. However, be careful not to overfill the engine. In addition to the problems caused from overfilling the crankcase, too much oil may cause leaks as the high-riding oil is more easily forced past seals and gaskets.
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