"Oil leak, but not excessive": what the MOT advisory means
"Oil leak, but not excessive" is an oil leak MOT advisory. It means the tester saw oil seeping from the engine or gearbox, but not enough to fail the car. It's one of the most common advisories on older cars. Most of the time it's a tired gasket or seal. You don't need to rush, but check your oil level every couple of weeks and find out where it's coming from before it gets worse.
When an oil leak fails the MOT
The MOT manual's fluid leak rules aren't specific to oil. A leak fails as a major defect when it's excessive and likely to harm the environment or be a risk to other road users. A leak that's continuous and a serious risk to road safety is dangerous.
The manual gives testers a measurable line: a leak fails if it forms a pool on the floor more than 75mm across within five minutes. Several small leaks together can fail if they add up to the same rate.
One useful detail: coolant, screenwash and SCR fluid (AdBlue) leaks aren't a reason for failure on their own. Oil, fuel, brake fluid and power steering fluid are the ones that matter.
Where small oil leaks usually come from
| Source | What you'll see | Rough repair cost |
|---|---|---|
| Sump plug washer | Drips from the plug at the bottom of the sump | £10 to £30 |
| Oil filter not sealed | Oil around the filter housing | £10 to £40 |
| Rocker (cam) cover gasket | Oil down the top edges of the engine | £80 to £200 |
| Sump gasket | Oil around the bottom of the engine | £120 to £300 |
| Front crankshaft or camshaft seal | Oil behind the timing cover or pulleys | £150 to £450, more if the cambelt comes off |
| Rear crankshaft seal | Oil between engine and gearbox | £400 to £800 or more, because the gearbox comes off |
| Turbo oil feed or return pipe | Oil around the turbo on diesels | £80 to £300 |
Prices are rough independent garage figures and vary a lot by engine. The rear crankshaft seal (often called the rear main seal) is the one that hurts, because of the labour.
How to find where it's coming from
Oil runs downhill and gets blown backwards by air under the car, so the wet patch is often a long way from the leak. The trick is to start clean.
- Have the engine and the area under it degreased, or do it yourself with an engine degreaser and a hose on a cold engine.
- Drive normally for a few days.
- Look for the highest point that's wet. That's usually the source.
- Leave a sheet of cardboard under the engine overnight. The colour helps: engine oil is brown to black, automatic gearbox fluid is often red, coolant is green, pink or blue, and brake fluid is clear to yellowish and feels slippery.
Why it's worth fixing even if it's small
A seep rarely stays a seep. Oil dripping onto a hot exhaust smokes and smells, and in the worst case it's a fire risk. Oil soaking into rubber parts like engine mounts and bushes makes them go soft. And a leak that's ignored for long enough can let the engine run low, which can cost far more than any gasket.
If the oil level drops noticeably between checks but there's no visible leak, the engine may be burning it instead. That's a different problem, so mention it to the garage.
What to do now
Check the dipstick with the car on level ground and top up to the right level with the grade in your handbook. Then get the leak traced at the next service, or sooner if you're topping up regularly.
If your MOT also mentioned the exhaust, read the exhaust advisory guide. For everything else on the result, paste it into the MOT advisory decoder.
Got more than one advisory?
Paste your whole MOT result into the decoder. It explains every line, sorts them by urgency and adds up a rough repair budget.
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