MOT advisory explained
“Oil leak, but not excessive”
Your MOT passed, but the tester found oil where it shouldn’t be. This is the advisory drivers ignore more than any other — and the numbers suggest they are not wrong to.
The tester found oil seeping from your engine or gearbox, but not enough to drip onto the ground. That is the whole distinction: a film, a weep or a damp patch is an advisory, while oil actually falling is a failure.
Seals harden gradually rather than giving way, so this one usually has a long runway. What it does not have is a way of fixing itself.
The range is unusually wide because it spans four different jobs — a valve cover gasket at the bottom, a crankshaft seal at the top. Which one you have is the only question that matters.
Half an hour on a ramp turns a £650 spread into a number. Pay for the diagnosis before you authorise anything else — it is the cheapest money you will spend on this.
An “oil leak, but not excessive” advisory means the tester found oil seeping from the engine or gearbox but not dripping, so the car passes. Fixing it costs £150–£800 depending on which seal. Of 8.9 million tracked oil leak advisories, only 1.3% later returned as a failure.
What the tester actually saw
On the ramp, with the underside of your car at eye level, oil seepage is obvious in a way it never is on a driveway. The tester is looking for wet, oily film on the engine, gearbox, sump or axle — usually with road dirt stuck to it, because oil attracts grime and builds a dark crust around wherever it’s coming from.
The word doing the work is “excessive”. An MOT fails an oil leak only when it’s severe enough to drip — the standard is roughly whether oil would fall to the ground while the vehicle is being tested. A film, a weep, a damp patch that hasn’t formed a drop: all of that is an advisory. Oil actually falling: that’s a failure.
So the tester isn’t saying your engine is in trouble. They’re saying they can see oil outside the engine, they’ve judged it under the failure threshold, and they’re noting it because it won’t fix itself.
Not every fluid counts here. This item covers oil and other fluids that make a road surface hazardous, but coolant, screen wash and AdBlue are specifically excluded from it. A puddle of pink or blue under the car is a different conversation, and not this advisory.
Where oil leaks come from, cheapest first
- Valve cover gasket — the most common and the cheapest. A rubber seal along the top of the engine that hardens with heat cycles until it stops sealing. Oil weeps down the side of the engine block from above. £150–£250 at an independent garage.
- Sump gasket or sump plug — oil pooling at the lowest point of the engine, sometimes just a plug washer that wasn’t replaced at the last service. From £120 for a plug and washer, £200–£350 for a sump gasket.
- Crankshaft or camshaft seals — the expensive end, because reaching them means dismantling the front of the engine. £400–£800 depending on the car, and often bundled with a cambelt change if the timing cover has to come off anyway.
- Gearbox and axle seals — a different, heavier oil, usually thicker and darker than engine oil and located further back. Cost varies enormously with the gearbox.
A garage can usually tell you which within half an hour on a ramp, sometimes using UV dye where it isn’t obvious. That diagnosis is worth paying for before you authorise anything else, because it is the difference between the two ends of a £650 range.
When “not excessive” becomes a failure
The threshold is drips. If oil is falling from your car onto the ground during the test, that’s a failure — and rightly so, since oil on a road surface is a hazard to motorcyclists and cyclists in particular.
Unusually for an advisory, the line is written down and measurable. The inspection manual describes it in observable terms — a leak forming a spot of around 75 mm within roughly five minutes of watching. That makes this one of the few items on a certificate where “excessive” is an observation rather than an opinion.
Which puts it at one end of a spectrum worth knowing about. Brake pads have a published figure too, 1.5 mm for every car. Brake discs have a number, but it belongs to the manufacturer and is stamped on the part. An exhaust leak has no number at all. Four items, four different answers to the same question — and it explains why some advisories are arguable and others are not.
There’s a second failure route worth knowing: oil contaminating something it shouldn’t. Oil on a brake disc or a tyre, or soaking a suspension bush, fails the test on its own terms regardless of how much is leaking. A slow leak that happens to drip onto a brake component is a bigger problem than a faster one dripping harmlessly onto the road.
Between advisory and failure, though, there’s usually a long runway. Seals harden and weep gradually, and most leaks flagged as “not excessive” stay that way for a considerable time.
How often does this advisory become a failure?
Rarely, and we’d rather tell you that than pretend otherwise. The DVSA test record tracks every advisory forward to the same vehicle’s later tests, so it’s possible to measure what actually happened to nearly nine million oil leak advisories.
| What happened next | Oil leak | Suspension | Brake parts |
|---|---|---|---|
| Became a failure at a later test | 1.3% | 18.7% | 9.4% |
| Ignored, no action taken | 43.5% | 37.1% | 36.1% |
| Fixed | 55.1% | 44.2% | 54.4% |
| Median advisory to failure | 379 days — the next MOT | ||
Calculated from the DVSA MOT test database (Open Government Licence v3.0), from 8,890,638 tracked oil leak advisories. “Became a failure” means an oil leak was recorded as a major or dangerous defect at a following test.
An oil leak advisory becomes a failure 1.3% of the time — the lowest figure of any category we have measured, fourteen times less likely than a suspension advisory and seven times less likely than brake parts. Ninety-nine times in a hundred, the car that passed with this note passes again.
It is also the most ignored advisory we have measured. 43.5% were still there at a later test, unfixed and recorded again — a higher share than any other category we have measured. Drivers are, in other words, leaving this one alone more than anything else on the certificate.
Across every other category, ignoring an advisory and it becoming a failure move together: suspension is ignored 37.1% of the time and converts at 18.7%, brakes 36.1% and 9.4%, body and structure 28.2% and 11.8%. Oil leaks break the pattern completely — the most ignored of the six, and by a wide margin the least likely to convert.
That is not carelessness showing up in the data. It is nine million drivers collectively working out which advisories carry consequences and which do not, and getting it right. If your goal is to pass the MOT, leaving a non-dripping oil leak alone is a sound bet, and it would be dishonest of us to imply otherwise while the figures sit there.
But the MOT is not an engine health check, and that is the part the numbers cannot tell you. The test asks one question — is oil reaching the road — and never asks where the oil went, whether the level is dropping, or what the seal will do in another two winters.
So: don’t panic, and don’t rush. Do check your oil level monthly, and do get the source identified while the diagnosis is cheap — because the difference between a £150 gasket and an £800 seal is entirely about which one it turns out to be, not about how long you waited.
How to work out if it’s getting worse
- Check your oil level monthly. This is the single most useful thing you can do, and it measures the thing the MOT does not. A leak that isn’t costing you oil between services is genuinely minor; one that needs topping up every month is telling you something different, whatever the certificate said.
- Look at where you park. Put a sheet of cardboard under the engine overnight. Nothing on it after a week means the tester was right that it isn’t dripping. Spots that grow week by week mean it’s progressing.
- Note the colour. Fresh engine oil is amber, old engine oil is black, gearbox and axle oil is thicker and often darker with a distinctive smell. It helps a garage narrow down the source before they’ve even lifted the car.
- Watch for smoke or smell after a run. Oil dropping onto a hot exhaust burns off with a distinctive acrid smell and sometimes visible wisps from under the bonnet. That’s worth acting on sooner — not because of the MOT, but because it’s a fire risk in the worst case.
What it costs
| Source of the leak | Price fitted | Notes |
|---|---|---|
| Sump plug and washer | From £120 | Sometimes just a washer missed at a service |
| Valve cover gasket | £150–£250 | The most common source by some distance |
| Sump gasket | £200–£350 | The sump has to come off |
| Crankshaft or camshaft seal | £400–£800 | Front of the engine comes apart |
Independent garage prices, parts and labour. Main dealers typically charge around 50% more. Gearbox and axle seals vary too widely by transmission to give a useful range.
The spread on this advisory is wider than on anything else in the section, and it is entirely about which seal rather than which car. That is why the diagnosis is worth more here than anywhere else: half an hour on a ramp moves you from a £650 range to a figure.
Ask whether anything else is due at the same time. A crankshaft seal sits behind the timing cover, so if a cambelt is anywhere near due, doing both together saves paying twice for the same strip-down. This is the one place on the page where the expensive option can be the cheaper one.
Stop-leak additives are worth being honest about. They work by swelling rubber seals, and on an old car with a weep and a limited future they occasionally buy time. They do not repair anything, they can affect seals you did not want swollen, and no garage will guarantee the result.
| Worked example — valve cover gasket, family hatchback | |
|---|---|
| Gasket set, quality aftermarket | £25 |
| Labour — 2 h × £65 | £130 |
| Typical total | ≈ £155 |
At the very bottom of the £150–£800 range, which is where the most common source happens to sit. A crankshaft seal on the same car is several times this, and the only way to know which you have is to look.
Enter your reg — we’ll pull every advisory from every test, show whether this leak has been flagged before, and price the likely fixes.
What to do next
- If it’s the first time you’ve seen this advisory: check the oil level, put cardboard under the car for a week, and note what you find. That costs nothing and tells you most of what you need.
- If it’s appeared two or three years running: get the source identified. A repeating advisory means the seal has been deteriorating throughout, and the cheap end of the price range is only available while it’s still the cheap component.
- If the level is dropping between services: that’s the signal that matters more than the MOT note. Book the diagnosis regardless of what the certificate says.
- If you’re buying the car: an oil leak advisory alone isn’t a reason to walk away — most cars over a decade old have one. A leak plus low oil, or a leak that’s been flagged three times, is a different conversation and worth using in the negotiation.
Oil leak advisory FAQ
Is an oil leak advisory serious?
Usually not, in MOT terms — an advisory means the tester judged it below the failure threshold, which is oil actually dripping. But it’s worth checking your oil level monthly, because the test only asks whether oil reaches the road, not whether your engine is losing it.
Will an oil leak fail my MOT?
Only if it’s dripping — oil falling from the car during the test fails, a film or a weep doesn’t. There’s a second route: oil contaminating a brake component or a tyre fails on its own terms regardless of quantity. In practice, only 1.3% of oil leak advisories become a failure at a later test.
How much does it cost to fix an oil leak?
£150–£250 for a valve cover gasket, £200–£350 for a sump gasket, and £400–£800 for a crankshaft or camshaft seal where the front of the engine has to come apart. The spread is why the diagnosis matters — half an hour on a ramp tells you which end of that range you’re looking at.
Can I just top up the oil instead of fixing the leak?
For a genuinely minor seep, topping up between services is what a lot of owners do, and for an older car it can be the sensible economic choice. What you shouldn’t do is stop checking — a leak that gets worse without you noticing is how a cheap gasket becomes an expensive engine.
What’s the most common cause of an oil leak?
The valve cover gasket, by some distance. It’s a rubber seal along the top of the engine that hardens with heat cycles until it stops sealing, and it shows as oil weeping down the side of the block. It’s also the cheapest to fix, at £150–£250.
How do I know where the oil is leaking from?
A garage can usually tell within half an hour on a ramp, sometimes using UV dye if it isn’t obvious. At home, cardboard under the car overnight shows you roughly where it’s landing, and the colour helps — amber or black is engine oil, thicker and darker with a strong smell is usually gearbox or axle.
Is it safe to drive with an oil leak?
A seep flagged as “not excessive” is generally safe to drive with, provided you keep the oil level topped up. What isn’t safe is oil dripping onto a hot exhaust — that smells acrid after a run and is a genuine fire risk — or oil reaching a brake disc, which affects stopping.
Does a coolant or screen wash leak count as this advisory?
No. This item covers oil and other fluids that would make a road surface hazardous, and coolant, screen wash and AdBlue are specifically excluded from it. A pink or blue puddle under the car still needs looking at, but it is a different question and not this advisory.
How often does an oil leak advisory become an MOT failure?
1.3% of the time — the lowest of any category we have measured, against 18.7% for suspension and 9.4% for brake parts. It’s also the most ignored of those six, with 43.5% still unfixed at a later test. Drivers leaving it alone are making a reasonable bet as far as the test is concerned — just keep an eye on the oil level, which the MOT doesn’t measure.