If you ask 10 drivers when they last checked their engine oil, eight will say “ages ago” and the other two will say “at the petrol station.” Both groups are mostly checking it wrong. The dipstick has been on cars for over a century. It is the single most useful diagnostic tool a driver has, and it takes 90 seconds to use properly.
Here is what the manuals don’t tell you.
When to check it
Cold, in the morning, before the car has been started. This is the gold standard. Oil has had hours to drain back into the sump from the engine top end. The level on the dipstick is the actual quantity in the engine.
At least 10 minutes after switch-off, on level ground. If you must check warm, give the oil time to settle. The 30 seconds after a long drive is the worst time — half the oil is still in the head, on the camshafts, and dripping back down. You’ll read low and add oil that doesn’t need adding.
Not at the petrol station. Forecourts are sloped for drainage. Even a 2-degree slope shifts the reading enough to cause overfilling. If you check at a servo, find a flat section of car park, not the pump area.
The actual procedure
- Park on level ground. Engine off. Bonnet open.
- Find the dipstick. Usually has a yellow or orange T-handle. Modern cars increasingly hide it under plastic covers or replace it with an electronic gauge.
- Pull the dipstick out fully and wipe it clean with a paper towel or a clean rag. Don’t use tissues — they shred and leave fibres.
- Push the dipstick fully back into its tube. Hold for two seconds to settle.
- Pull it out smoothly, hold it horizontally so the oil doesn’t run, and read both sides.
Step 3 is the one most people skip. The first read is contaminated by oil splashed on the dipstick during driving, sitting in the dipstick tube. The reading is always too high. Wipe, re-insert, then read.
Reading the level
Dipsticks have two marks: an upper “max” line and a lower “min” line. The distance between them represents approximately one litre of oil in most engines.
Halfway between min and max is ideal. Right on the max is too full. Right on the min means you’re a litre down and should top up before driving any distance.
Below min is a problem. The engine has either burnt or leaked oil. Adding a litre to bring it to halfway is fine as a short-term fix, but find out where the oil went before the next service.
Above max is also a problem. Overfilling causes oil to be churned by the crankshaft, which creates foam, which doesn’t lubricate. Long-term overfill damages seals from the increased crankcase pressure. If you’ve overfilled, drain the excess.
What the oil itself tells you
The colour and texture of the oil on the dipstick is diagnostic.
Honey or amber. Fresh or near-fresh oil. Engine in good condition.
Light brown. Normal for oil that’s been in service for a few thousand kilometres. Still has detergents working.
Dark brown to black. Either due for a change (most modern oils darken normally) or contaminated with soot from inefficient combustion. Black oil at a low mileage interval suggests a problem; black oil at 8,000 km is expected.
Milky or mayonnaise-coloured. Coolant is mixing with oil. Head gasket failure, cracked head, or in rare cases a cracked block. This is a stop-driving signal. Get the car towed to a workshop.
Frothy. Aeration. Could be from overfilling, a failing oil pump pickup, or a leak letting air into the oil pump. Investigation needed.
Metal flakes visible under a torch. Internal engine wear. Bearings or gears generating debris. Worth a workshop visit.
Strong fuel smell. Petrol contamination. Either a failed fuel injector dumping fuel into the cylinder, or excessive short-trip driving where fuel doesn’t burn off the cylinder walls. Becomes a problem long-term because fuel-thinned oil doesn’t lubricate properly.
What about the smell
Healthy engine oil has a slight burnt-petroleum smell. Sweet or fruity smells suggest coolant contamination. Strong petrol smells mean fuel dilution. Sulphur or rotten-egg smells can indicate catalytic converter failure that has worked back through the system. Trust your nose.
How often to check
The owner’s manual for most modern cars says monthly. Realistically:
Older cars (10+ years) or high-mileage (over 150,000 km). Weekly. Older engines burn oil; catching it early prevents a low-oil failure event.
Modern cars (under 5 years), low mileage drivers. Monthly is fine.
Any car that’s used hard — towing, long highway, performance driving. Every refuel until you know its consumption rate.
Before any long trip. Always.
A surprising number of warranty claims on new engines come down to drivers who never checked oil, ran the engine low, and caused damage that the manufacturer is entitled to refuse to cover.
Topping up
If the level is low, top up with the same grade and specification as the existing oil. Mixing grades isn’t ideal but isn’t catastrophic for a single top-up. Mixing specifications (e.g., adding a standard oil to an engine specced for a low-SAPS oil like VW 504.00) does cause damage long-term, particularly to DPFs and catalytic converters.
Pour slowly. Modern engines have small oil filler necks and tight engine bays. A funnel is worth keeping in the boot. Check the level after pouring, before driving, before assuming you’ve added enough. It’s easy to underestimate from a half-empty bottle.
What modern cars are doing differently
Many recent cars (BMW post-2014, some Audi, Mercedes, and increasingly Mazda) have eliminated the physical dipstick. The oil level is read electronically and displayed in the infotainment system. The reading is generally accurate but has caveats:
- Only valid on level ground
- Requires the engine to be warm and shut down for a specific time (often 5 to 10 minutes)
- The car may not warn you of low oil until it is dangerously low
- The procedure to check varies by model and is buried in a menu
If your car has an electronic gauge, learn the procedure from the owner’s manual before you need it. Discovering the menu when the oil light comes on is bad timing.
What burning oil tells you
If you find yourself topping up oil between services, something is consuming it. The two paths are:
Internal consumption. Worn piston rings, valve stem seals, or PCV system issues let oil into the combustion chamber where it burns. Blue smoke from the exhaust on startup or under throttle is the giveaway. Many older Subarus, BMWs, Audis, and some modern turbo Hyundais are known oil consumers within manufacturer-accepted limits.
External leaks. Oil dripping from the engine onto the road or onto the underbody splash shields. Inspect underneath after the car has sat overnight on a clean surface. Sources: rocker cover gasket, rear main seal, sump gasket, oil cooler lines, turbo seals.
A litre per 5,000 km is high but not abnormal for many engines. A litre per 1,000 km is a problem that needs diagnosing.
Frequently asked questions
Can I check oil right after I switch off?
No. Wait 10 minutes for the oil to settle. Reading immediately gives a false-low result.
Why does the manual say “lifetime fluid”?
Marketing rather than engineering. All oils degrade. The manual is technically describing the manufacturer’s minimum warranty obligation, not the optimal service interval.
Is fully synthetic worth the extra cost?
For modern engines with tight tolerances and turbocharging, yes. For older naturally-aspirated engines, semi-synthetic is fine and arguably better.
What if I overfilled? Do I have to drain?
A small overfill (a few millimetres above max) is generally fine. Significant overfilling (15 mm or more above max) should be drained. A workshop can vacuum-extract excess through the dipstick tube.
My oil looks fine but the change interval is up — do I really need to change it?
Yes. Oil degrades chemically as well as visually. Detergent additives deplete, viscosity stabilisers break down, and acidic combustion byproducts accumulate. Visual cleanliness is not a substitute for service.
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