Car Oil Leaks: Common Signs & Causes
Corner Park Garages, Swansea and Cardiff
May 21, 2019 at 2:21 PM
Noticing that your car has an oil leak is a common problem amongst drivers, but it doesn't necessarily have to be an expensive repair. As soon as you're aware of an oil leak, you should try to determine the cause and have it fixed.
Oil is used to lubricate the car's engine and all of its moving parts to prevent friction. Without enough oil in the system, certain components will start to rub together and wear each other down eventually leading to mechanical failure. In the worst case scenario, the engine will seize up completely.
Depending on the location of the oil leak, it can pose a fire risk in the engine compartment - a leak in the valve cover gasket could allow hot and flammable oil to drip onto the exhaust manifold, which is also hot, causing smoke and potentially a fire.
An oil leak could be anything from a tiny pinhole in a gasket to a gushing hole from a bad seal. In any case, it's important to find the source of the leak and have it repaired so that the oil stays where it's needed most - inside the engine.
Common Signs Of An Oil Leak
Oil leaks aren't always obvious and visible. To help spot when your car is losing oil, there's a range of symptoms you can look out for.
OIL STAINS UNDER THE CAR WHEN PARKED
Sometimes an oil leak is really easy to see, especially when there's a dark puddle underneath your car. If you're able to park in the same place every day (e.g. on a driveway or in a dedicated space), it makes spotting the stain much easier.
However, if you have to park in different places, but suspect that your car has an oil leak, you can lay a piece of cardboard underneath the engine compartment to confirm the leak is from your car.
NOTE: If there is a fresh stain, make sure to take a closer look at the colour - a brown or black stain indicates an engine oil leak; however, if the liquid is red it's likely to be transmission fluid, whereas if the liquid is green or orange, the car is leaking coolant.
Typically, noticing an oil stain underneath a parked car indicates that the leak is coming directly from the oil pan or oil drain plug.
OIL LEVEL ON THE DIPSTICK DROPS OVER TIME
It's good practice to regularly check your oil level during general car maintenance checks you carry out yourself. You should be checking your oil at least once a month and before any long trips.
If you notice that the oil level on the dipstick is dropping quicker than expected, it's likely that you have an oil leak. Start checking the oil level every week to determine how serious the leak is.
Modern cars are able to go between 8,000 - 12,000 miles before needing an oil change because they use very little engine oil. As a result, any decrease in the oil level indicates a moderate to major oil leak.
BLUE SMOKE WHILE DRIVING
When you're on the road, check to see if there's any blue smoke coming from the tailpipe. If oil leaks into the exhaust manifold, smoke will be produced from the engine area.
As mentioned earlier, leaving this problem unattended could potentially lead to the car catching on fire while you're driving.
LOW OIL LEVEL DASHBOARD WARNING LIGHT
To help protect the undercarriage, many modern vehicles have shielding that will most likely catch any oil leaks, preventing them from collecting in a puddle on the road.
Although it doesn't automatically mean that your car has an oil leak, the low oil level dashboard warning light alerts you if the oil level or oil pressure is lower than normal.
From here, you can use the dipstick to check the current oil level and top it up. You should then check it a few hours later or the following day. If the level has dropped in this time, your car has an oil leak.
As well as lubricating the engine and all its parts to prevent friction, engine oil serves to regulate the engine's temperature. Without proper lubrication, the crankshaft, connecting rods, pistons and piston rings will grind against each other producing vast amounts of heat.
In the event of this happening, the engine temperature sensor should start to rise which could indicate a lack of oil caused by an oil leak. If the engine oil drops too low, the engine could overheat, seize-up and stall.
BURNING OIL SMELL
While you're driving, you might notice an unpleasant smell as oil leaks onto the hot metal parts of the engine and starts to burn. The smell might not become apparent until you've reached the end of your journey and got out of the car.
Common Causes Of An Oil Leak
The cause of an oil leak is often linked to the symptoms your car exhibits.
DEGRADED OIL GASKET
The most common cause for a car oil leak is a damaged oil gasket - this is a seal that joins two metal components in the engine. Over time, oil creates sludge or gunk in the engine which causes the gasket to break down, allowing oil to seep through.
DAMAGED OIL PAN
The oil pan is located on the underside of the car and is exposed to the debris on the road. Throughout the course of normal driving conditions, materials such as rocks and stones can collide with the oil pan.
When this happens, they can leave small dents in the oil pan that can create tiny holes and cause the seal to become loose. Typically, the oil leak will become obvious when the car is parked for a long time and leaves an oil stain on the road.
DEGRADED OIL DRAIN PLUG
In order to change a car's oil, you have to remove the oil drain plug (also known as the sump plug) - located at the base of the oil pan - so that the old oil can filter out. Before filling the car with the new oil, the oil drain plug needs to be replaced and tightened appropriately. If it's a little bit loose, some oil will escape, thus causing a leak.
Similarly, the oil drain plug can become worn out or loosened by flying road debris. Fresh oil gathered around the plug is an indication of a leak.
Usually, an oil leak as a result of a part being incorrectly installed is down to a DIY job rather than a trained mechanic making a mistake - although this can still happen.
It's possible that one of the gaskets has been over-tightened or that the tightness is not evenly distributed. Alternatively, the oil filter might not have been fitted correctly after the last oil change, or the oil filter could have been pierced if the oil filter wrench was too tight.
OIL FILLER CAP
The oil filler cap covers the engine oil compartment to prevent contamination. You need to remove it in order to add new oil during an oil change or to top the oil level up if it's too low.
If the cap is loose, broken or missing, it's possible for the oil to spill out while you're driving. When this happens, the engine and other components under the bonnet will be covered in oil and it will continue to drip once you've parked up.
Why Is My Car Leaking Oil After An Oil Change?
Changing your car's oil at regular intervals is crucial to the health of your engine. The process involves removing the old oil by releasing the sump plug, letting it filter out and replacing it with new oil.
As well as new oil, your car will also get a fresh oil filter which helps to remove contaminates from the engine oil to keep it as clean as possible.
After completing this process, it's possible that oil will be leaking from your car. Normally, this will be because of the drain plug, an issue with the oil filter or a build-up of additives in the old oil.
LEAKING FROM THE DRAIN PLUG
It's not unusual to have a few oil drips after an oil change; however, a consistent flow that is able to create a puddle is too many and the drain plug is causing an oil leak.
The cause of the leak could be as simple as the sump plug not being tightened all the way. To fix this, you need a properly sized wrench to tighten the plug up properly.
If the plug has been tightened correctly, there could be an issue with the gasket - either it's worn or dirty. When this happens, the drain plug won't have a tight seal on the oil pan and you'll need to remove the plug and drain the oil again.
While the oil is draining, you can attempt to clean the part. If that doesn't look as though it will form a tight seal, you'll need to replace it with a new gasket.
ISSUES WITH THE OIL FILTER
Before the new oil filter is fitted, most mechanics will lightly wet the gasket at the top with the new oil to give it a stronger seal. As the filter gets put into place, it should be turned a further three quarters of a turn.
If there's a gap between the oil filter and the engine, it's not on tight enough and oil will be able to escape while you're driving.
BUILD-UP OF ADDITIVES IN THE OLD OIL
Old conventional oils were renowned for creating sludge or gunk in the engine, especially if the car went too long between oil changes. This build-up could block oil flow and often result in creating slow leaks.
Detergents and solvents are now included in engine oil to help remove gunk in the engine and prevent future build-ups. However, when the new oil is added after an oil change, it can escape through the previous slow leaks much quicker.
Fortunately, the fix is a simple one; a professional mechanic should be able to simply seal off the leak.
Is It Safe To Drive With An Oil Leak?
If you know your car has an oil leak, it's not advisable to drive it largely because it's a fire risk and the engine could seize-up unexpectedly which would put you and other road users in danger.
However, short distance journeys around 10 miles or less are not as likely to reduce your oil levels to a dangerous point unless you have a severe oil leak. Similarly, as long as the level of your engine oil doesn't drop below the minimum, your car should be fine to drive.
The biggest risk factor for driving with an oil leak is its size and location. Even a small leak from the valve cover gasket will drip oil on the hot exhaust manifold which can potentially cause fire. Alternatively, the lifespan of the timing belt or engine drive belts can be shortened by small leaks from the front crank seal or the timing cover.
How Do I Stop An Oil Leak?
As soon as you notice an oil leak on your car, the best course of action is to book it in to your local garage for a trained mechanic to fix. Providing them with information on the symptoms of the leak and when it's most prominent will help them to diagnose where the leak is and make the repair quicker.