How to check your oil between changes (and what the dipstick is telling you)

Why bother, if we change it anyway

Because engines use oil between changes, and some use quite a lot. Many modern engines are considered normal by their own manufacturers at a quart every 1,000 to 2,000 miles, especially turbocharged ones and anything past 100,000 miles. On a 7,500 mile interval that is several quarts gone, and an engine running two quarts low is working with a fraction of the oil it was designed for. A monthly look at the dipstick is how you find out whether yours is one of those engines before the low oil light does.

It also catches leaks, a coolant problem, and fuel getting into the oil, all of which show up on the stick before they show up anywhere else.

The five minute version

1. Park on level ground. A driveway with a slope tilts the oil in the pan and the reading with it.
2. Engine off, wait five to ten minutes. Most manuals say to check warm, after the oil has had a few minutes to drain back to the pan. Some say check cold, first thing in the morning. Do whichever yours says, and do it the same way every time so the readings compare.
3. Pull the dipstick and wipe it clean. The handle is usually yellow or orange. Wipe with a paper towel or rag.
4. Push it all the way back in, wait a second, pull it out again. Read the side that shows a clean line, not the smeared one.
5. Read the level against the marks. Two dots, two lines, or a cross-hatched band. Anywhere inside the band is fine. Right at the top is full.

How much to add

On most cars and light trucks the distance between the low mark and the full mark is about one quart. If the level is halfway down the band, you are about half a quart low. Add a little at a time, wait a minute for it to drain down, and check again. Stop at the full mark. Overfilling is worse than being a little low: the crankshaft whips the excess into foam, and foamed oil does not lubricate or pump properly.

Use oil that meets the specification on your oil cap or in the manual. Mixing a quart of a different brand is fine as long as it is the right viscosity and meets the same standard. Keep a quart of the right stuff in the trunk. If you are our customer, ask and we will leave one with you at your next service.

What the oil on the stick is telling you

Amber to honey colored, translucent. Fresh oil. Normal for the first few hundred miles.

Brown to dark brown. Normal for oil that has been working. Synthetic darkens as it holds contaminants in suspension, which is its job. Color alone is not a reason to change it.

Black, thick, and gritty between your fingers. Well past due, or a very dirty engine. Book a change.

Milky, creamy, or tan like coffee with cream. Coolant is getting into the oil. Do not drive it. This is a head gasket or similar and it gets expensive fast if the engine keeps running.

Smells strongly of gasoline, level rising rather than falling. Fuel is diluting the oil, common on direct-injection engines that only do short trips. Take a long drive to burn it off and change the oil sooner than the interval.

Metallic glitter in the light. Something inside is wearing. Have a shop look before it gets worse.

Cars with no dipstick

A growing number of vehicles, including many BMW, Mercedes, and some newer GM and Ford models, have no dipstick at all. The level is read by a sensor and shown in a menu on the dash, usually under vehicle status or service. The procedure is the same in spirit: level ground, engine warm, and follow the on-screen instructions, which often want the engine running. Check it monthly the same as you would a stick. The sensor tells you the level, but it cannot show you the color or the smell, so the "milky oil" warning comes from a coolant level that keeps dropping instead. Watch that too.

The two signs that mean stop

• The red oil pressure light comes on while driving. Not the amber "change oil soon" reminder. The red one, shaped like an oil can. Pull over safely and shut the engine off. Running an engine with no oil pressure destroys it in minutes, not miles. Check the level. If it is fine, do not restart it; that is a pump or sensor problem and it needs a tow.
• Milky oil on the stick. See the table. Coolant in the oil is one of the few things where continuing to drive turns a repair into a replacement.

What we do about it

Every oil change we do includes a check of the level and condition before we drain, and we write the mileage on your service record. If your engine is consuming oil we will tell you how much it was down and how far you had driven, so you know how often to check and how much to expect to add. If it is losing oil to a leak, we photograph where it is coming from so your repair shop does not have to hunt for it. The full list of what an inspection covers is in the FAQ.