Oil leak but not excessive – what it means (and how to fix it)

Hearing your car has an oil leak isn’t something that most people want to hear. However, sometimes this isn’t as bad of an issue as you think it is.

In this article we’re going to go through exactly why you might have got “oil leak, but not excessive” as an MOT advisory, whether it’s something you need to worry about and how you go about fixing it. 

What does “oil leak, but not excessive (8.4.1 (a) (i))” mean on an MOT?

To be honest, this means exactly what it says – you’ve got an oil leak somewhere, but it’s not leaking enough to cause a concern. Of course, leaking oil is always a problem, and if you let it get too bad, you could be causing a hazard to other road users by leaving oil all over the road, as well as causing serious damage to your engine.

However, what can be diagnosed as an oil leak might actually not be a serious issue. See, an MOT tester won’t do any investigation into the cause of a problem – they will simply identify issues from a checklist they have and move onto the next area of inspection.

So if they see oil staining on any part of the engine while inspecting, they will mark it down as an oil leak but not excessive. An excessive oil leak would usually mean there’s visibly oil dripping from the engine or from the sump, and this would likely fail an MOT.

So, for example, if you had your car serviced a few weeks before your MOT, and the person who serviced your car spilled a little oil somewhere in the engine bay and didn’t clean it up properly, your MOT tester could identify this as an oil leak. So you might not even have a leak, it just may look like you’ve got one.

Additionally it may be a case of your last mechanic not torquing the drain plug up properly causing oil to weep out of the sump, or possibly the oil filter again wasn’t screwed in as tight as it should have been or it’s worked its way loose and there’s a little leak of oil. 

However, a non-excessive oil leak could be due to something more serious – possibly you’ve got a damaged oil pan, a failed oil seal or perhaps your rocker cover hasn’t been sealed properly. If you’re unsure, your MOT tester should be able to tell you where the issue was identified and may be able to point you in the right direction as to how to get it fixed.

Fundamentally, if your car has passed the MOT, it’s not likely to be something that will cause you immediate problems, but if you do get oil leak but not excessive as an MOT advisory, you should get it checked into as soon as possible.

It’s also something you should consider in a car’s MOT history if you’re looking to buy a used car – if this has come up in an MOT during the last 12 months, you should make sure the owner has rectified the issue.

How do I get an oil leak but not excessive fixed?

Take your car to a garage and ask them to investigate it. However, you might want to do a bit of checking yourself first. Ask your MOT tester where they found the leak and ask them what they think should be inspected. However, if you’re not able to do this, and you’re able to get under your car and look into the engine bay, we’ve put this guide together to point you in the right direction.

If oil is dripping from under the car

This could be a couple of things – if oil is leaking from the sump, you’ll firstly want to check the drain plug is tight enough. If it’s so loose that you can unscrew it with your finger, you should get away with just tightening it up with a torque wrench to your vehicle manufacturer’s specifications and topping up the oil to ensure you’re not running your engine low on oil (depending how much has leaked out).

You might also have a failed sump gasket – and this is something a garage should be able to fix for you relatively inexpensively – providing you’ve caught the issue early on and you haven’t run the engine on low oil. You should be checking your engine oil pretty regularly anyway, which would make sure you were aware if you were losing oil.

Be careful with assuming oil is coming from under the engine, however – it could be coming from somewhere else, running down and dripping out from under the sump, so make sure you check over the entire engine first before getting under the car.

If oil is all over the gearbox 

Your gearbox will be mounted at the front of the car, as it’s mated to the engine.

Firstly you need to ensure that the leak isn’t gearbox oil – so you should check the gearbox itself to make sure it isn’t leaking. An MOT tester pushed for time might not notice and may just assume it’s engine oil – gearbox oil can also be pretty black and dark in the same way that engine oil can be (especially if it’s not fresh, and very few people get a manual gearbox serviced).

If you’ve established the gearbox is fine, it’s probably the rear main seal that’s leaking. This is unfortunately a big job that requires removal of the gearbox and clutch assembly – so you’ll want to book your car into a garage and be prepared for a significant bill.

If oil is all over the oil filter

It’s almost certain that your oil filter is leaking. If you’ve recently had a service it’s possible it wasn’t tightened up correctly or possibly was tightened too much – an oil filter should be just past hand tight.

An oil filter also has a seal inside which may have failed. Changing the oil filter is pretty simple on most cars and you should give it a try if you feel this is the issue, especially if you haven’t serviced the car in a long time and the oil filter has failed. Make sure you backfill the oil filter housing if required, and ensure you drain the engine of oil first.

If oil is leaking from the top of the engine

This could indicate an issue with the valve cover or rocker cover gasket. The rocker cover protects the components inside the cylinder head, and the gasket provides a seal between the engine block and the rocker cover – and this may have failed. 

Unfortunately the only way you’re going to fix this is by having the rocker cover re-sealed – which a garage should be able to do for you again at relatively low cost. 

If oil is leaking from the rear of the engine

This could be a camshaft seal leak – and this is common on cars with a timing belt rather than a chain. If you have a camshaft leak you may also smell smoke when driving and sometimes can see visible puffs of smoke coming from the engine bay. 

If the oil is leaking from the front of the engine

This could be your front main seal, or front crankshaft seal as it’s known. If the front crankshaft seal fails, you might see a visible leak at the front of the engine. If it’s a small leak you may notice an accumulation of oil underneath the engine.

If your car has a timing chain it could also be a timing cover leak – again, this is something you should get checked out by a garage. Even if your car has a timing belt, some cars have timing belts that run in oil, so you should get this checked out if you’re not sure which one your car has.

A word on blue smoke 

If you’ve noticed your oil level decreasing but can’t spot an obvious leak, and the smoke coming out of your car’s exhaust is blue, it’s likely that there is no external leak, and your engine is burning oil. Oil is leaking into the combustion chamber, where it’s being burned along with the fuel. This is normally associated with an unpleasant smell. This is something you need to get checked out as soon as possible with a garage.

Is a small oil leak serious?

So if your oil leak is so small that it’s literally just a weep, and there is no visible oil dripping out when you leave your car parked, it’s probably not something you need to deal with or worry about immediately.

However, oil leaks can quickly get a lot worse, and if you ignore them for too long, you can cause irreparable damage to your engine by running it low on oil. If a gasket or seal is failing, you might go out one day in your car and not be able to get home. 

If you’ve been advised to get your oil leak looked at by your MOT tester, get it checked out sooner rather than later to avoid doing further damage to your car. You wouldn’t be happy if your engine was leaking, you ignored it and caused terminal damage by running the engine low on oil and it turned out to be something simple like a loose drain plug that could be solved in seconds.

What’s also highly important is checking your oil on a regular basis – you should be doing this even if you haven’t been advised of an oil leak, but you should be checking meticulously if you have had “oil leak but not excessive” on your latest MOT. 

Is it normal for a car to leak a little oil?

If you’ve got a really, really old car, then maybe it’s normal for the oil to leak out a tiny bit. However if your car was manufactured in the last 20 years it shouldn’t be leaking oil if everything is normal. If your car is leaking, there’s an underlying problem somewhere that needs to be addressed. 

Modern cars don’t leak oil during normal operation. If your car is leaking oil, there is a problem that you need to have looked at.

How expensive is it to fix an oil leak?

You might as well be asking “how long is a piece of string”. It’s impossible to give a figure to this as it could be any one of a number of problems causing your engine to leak oil. You might get in and out of the garage in ten minutes without being charged because your oil filter wasn’t screwed in enough, or if you’ve left an oil leak for some time and it’s caused damage to your engine, you could be looking at the cost of an engine rebuild. It’s impossible to say exactly how much it will cost to fix an oil leak unless you know where the problem is.

What is the most common oil leak?

If I had to pick one it’s probably the rocker cover gasket, especially if it’s an older car. You’ll know this is the problem if oil is leaking from the top of the engine and you can see it all over the engine bay. 

Additionally if your car doesn’t have an undertray, it might end up being that your sump has been damaged by a rock or something and is leaking, or the sump gasket might have failed.

When should I worry about an oil leak?

If you can see a puddle on the ground, don’t start your engine. This is when you should be really, really worrying about it – as starting the engine is going to cause damage, especially if enough oil has leaked out that your engine won’t be properly lubricated.

If you can see little droplets on the ground but nothing significant, you can still drive the car (as long as you keep a close eye on your oil level) but get it booked in with your local garage ASAP. 

If you care about your car, don’t ignore an oil leak.

Check out some more of our servicing & maintenance related articles!