Causes of A car leaking oil
Leaking fluids, especially oil leaks, are one of the most common reasons why your car will need to be repaired at some stage in its life. It's also one of the main reasons why cars can eventually break down.
The two most common places for oil to leak from a car, are the engine and the transmission.
A car oil leak is often caused by a failed gasket or rubber seal. Gaskets and seals have a limited lifespan, and will fail eventually. Most oil seals and engine/transmission gaskets are made from soft materials such as rubber, silicone or cork. These can harden and crack overtime if they are constantly exposed to excessive heat and pressure.
In this article, I'll explain the most common reasons why oil is leaking from your car, how you can fix it and how much it's likely to cost.
How can you tell if it is engine oil that is leaking?
Most cars will have a few different fluids in the engine and gearbox to enable it to run smoothly. If you come across a fluid leak on the pavement, how can you tell if it is engine oil, or if it is a different fluid?
When it comes to leaking fluids there are five or six possibilities, depending on how old your car is.
- Engine Oil - Unless it has just been changed, then engine oil is usually light or dark brown or even black in color. It can smell like plastic if new, or more like cooking oil if it is old. If you are looking at it on the pavement, then it may be dark in color and if wet can look like a rainbow from certain angles.
- Fuel (Petrol or diesel) - Petrol and diesel are usually fairly easy to identify because of their distinctive smell. Petrol tends to dry out and evaporate fairly quickly in small quantities. When it's wet, it can be golden brown in color. Diesel is darker in color, and usually has a bluish tint.
- Transmission Fluid - New transmission fluid can be red in color when new, but sometimes it resembles engine oil in color and consistency. It can sometimes be difficult to distinguish from engine oil and it may only become obvious when you find the source of the leak.
- Engine Coolant - Engine coolant can be pink, blue or green in color. Check the color in the coolant top-up bottle to see if it matches the color of the leaked fluid. If the fluid is low in the bottle it may indicate a leak somewhere in the coolant system. Coolant can also be identified by its smell, which is usually usually sweet like candy floss.
- Brake Fluid - Brake fluid is light brown in color, sometimes almost clear. Depending on it's age, it may have a distinctive smell. If you suspect a brake fluid leak then check the brake fluid reservoir. If the fluid level is very low then you should investigate it further, for safety reasons.
- Power steering Fluid (ATF) - Power steering fluid is used on older cars. It is red in color when new, and turns brown as it ages. It usually has a slightly burnt smell and thickish consistency. A power steering fluid leak is usually noticable around the power steering hose connections or around the top up bottle.
What are the most common symptoms of a Car Leaking Oil?
It's important to keep an eye on the various fluid levels in the engine of your car. Newer cars have lots of plastic covers and some don't even have dipsticks for checking the oil level.
This can make it more difficult to spot an oil leak, especially if it's only a small one. Here are some common symptoms that can be caused by a car leaking oil.
1. Low oil pressure light on the dash
If the engine oil pressure gets too low, you'll get a warning light or check engine light on the dashboard. Engine oil pressure should be between 30 and 45 psi when the engine is warm. If it is too low, this can indicate a low oil level caused by an oil leak.
It's normal for most engines to burn off a small amount of oil between oil changes. If you cover a lot of mileage in your car every year. If the engine is old, then you'll probably need to top up the oil every few thousand miles.
Low oil pressure can also be caused by an oil leak. If you find that you are topping up the oil more frequently than usual, this can indicate that oil is leaking from somewhere and you should investigate it further.
2. Ticking noise from the engine
A ticking, tapping or knocking noise from the engine when it is idling can indicate that the upper engine parts are not being lubricated properly. This can be caused by low engine oil levels, using the wrong specification engine oil, insufficient engine oil pressure or a problem with the timing belt or chain.
A common cause of strange noises from the engine is a persistent oil leak. If the engine is constantly losing oil, then the worst affected part of the engine are the valves and tappets (valve lifters). These can become worn and will become noisier due to a lack of lubrication.
3. Low oil level when dipped
If you dip the engine oil regularly and it is always low, it could be due to an oil leak. Most engines will "use" a small amount of oil over time. It's not uncommon for an older engine to use a litre of oil every few thousand miles. If you haven't checked the oil level in a few months then this could be the cause of the low oil level. A consistently low oil level, especially when topped up regularly is more than likely caused by oil leaking somewhere from the engine.
4. Oil on the pavement
One of the classic signs of leaking oil from a car, is a dirty oil patch on the pavement or in your driveway. This is usually an indication of a pretty bad oil leak, as the oil needs to work it's way down through the plastic engine covers (if fitted!) and onto the ground.
It's not always easy to pinpoint exactly where the oil is coming from, as it may be leaking from the top of the engine and is dripping down onto the lower engine components and then onto the ground.
It may also be caused by a leaky transmission. This is a very common cause of an oil leak under a car, and can be difficult to trace.
5. Dried oily residue on engine components
Not all oil leaks are the same, and some are small and will build up over a long period of time. If the oil leak goes unchecked, it will dry out and build up around the area it is leaking from. This can often be seen around oil filter housing leaks, or around a leaking oil sump gasket.
6. Your Transmission is having Trouble changing gears
If the transmission or gearbox is leaking fluid, then it's going to affect how smoothly it changes gear. It's not always easy to check the fluid level in the transmission or gearbox, but a leaky transmission usually has some fairly obvious symptoms.
The symptoms of low transmission fluid include difficulty changing up and down through the gears, slower gear changes, grinding noises when changing gears and transmission overheating.
You may also notice that the fluid leaking from the transmission is different in color to engine oil. If the fluid is fairly new then it will be a reddish color, instead of golden or dark brown engine oil. It can also be thicker in consistency than engine oil.
What are the most common reasons for oil leaks in cars?
There are a few reasons why your car is leaking oil.
1. The most common reason for car oil leaks is the failure of a rubber seal or gasket. Rubber seals are used in many parts of an engine where two components join together. Engines can get very hot, and some parts of the engine operate under huge pressures. The constant heating up and cooling down of the engine will cause rubber parts to harden as the age, and eventually crack.
Common places for seals to fail, and oil to leak from, are the oil sump gasket, the oil sump bung (nut), the oil filter housing (or rubber seal if it's a screw on filter type) and from the oil filler cap. You can also get oil leaks from the head gasket, but it's more common for the oil to leak into the coolant, rather than out of the engine.
Other places that are prone to leaks are the gearbox or transmission. These can leak at the sump or where they mate to the engine.
2. Badly fitted parts can also leak. If a replacement component is not tightened properly, the seal will leak. The seal can also fail if it is overtightened. This is why it's very important to use a torque wrench when working on your vehicle. For example, the bolts that are used on the oil sump or on the cylinder head need to be torqued to an exact tightness and tightened in a specific order. If not it will more than likely cause a leak.
3. Damage to the underbody of the car. Sometimes a leak can be caused by hitting a speed bump or a pot hole. Damage to the oil sump or the underside of the transmission is not uncommon and can cause leaks.
4. A loose oil filter. Many cars still use the screw on, canister type oil filter. This type of oil filter has a rubber gasket that creates a seal when tightened against the engine. This seal will wear out over time and can leak or cause the oil filter to loosen if the filter is not changed on schedule.
This is actually more common than you would think. Oil change intervals are getting longer, and this means that oil filters are not being changed as often. If you are changing the oil in your vehicle yourself, it's important to choose a good quality oil filter. There are 'extended life' oil filters available that can filter the oil effectively for longer periods, and most will have an upgraded rubber gasket or a silicone gasket that can last longer too.
How do you diagnose a car oil leak?
If you suspect that your car is leaking oil, then there are a few common sense steps you can take to identify where exactly it is coming from and if you can fix it yourself, or need a mechanic to do it for you.
If you haven't spotted any oil puddles on your driveway, or oil leaks around the engine bay, but the low oil pressure light shows up on your dashboard, the problem could be with the oil pump, the timing belt (or chain) or the oil pressure sensor switch.
If your car is leaking oil, then it's important to figure out where it's coming from. Here a the steps you should take to diagnose the problem.
1. identify the fluid type
Use the guidelines above to identify if the leaked fluid is engine oil or one of the other fluids in your car. If you identify it as oil, then it may be engine oil or transmission fluid/ gearbox oil. Sometimes they can be difficult to distinguish, especially if it's an older car.
If you are experiencing a problem with the transmission, such as shifting gears or a noisy gearbox, this may indicate a transmission fluid leak. If the low oil pressure light is coming on when you are driving, or you need to top up the engine oil more often than usual, then this will indicate a leak from the engine.
2. figure out where the oil is coming from
If the leak is bad enough, then it will be obvious where it is leaking from. Most of the time, leaks are small and may be more difficult to trace. If you are sure the fluid leaking is oil, then you'll need to take a close look at the engine bay and the transmission.
Start with the engine. Open the hood and have a look around the top, back, sides and underneath the engine for signs of a leak. Check the following areas of the car, as these are common places for leaks to occur:
1. Top of engine: Check for oil leaks and residue around the oil filler cap (remove and check the seal condition), intake manifold gasket, the CCV (crankcase ventilation valve), the EGR valve and any vacuum hose connections.
2. Side of engine: Check for possible leaks from the timing cover gasket, front and rear crankshaft seals and the valve cover gasket. Try removing one or more spark plugs. If you see oil on the spark plugs, this may indicate a leaking valve cover gasket.
3. Bottom of engine: Check for oil leaking from the oil filter, oil sump (small leaks can cause an oily residue to build up around the edge of the sump), the oil drain bung, the clutch bell housing (oil can leak from the seal between the gearbox and engine) or if it's an automatic transmission there may be oil leaking from input shaft seal near the torque converter.
4. Transmission/Gearbox: Check the front and rear of the transmission for leaks at the input seal (front transmission seal) or at the output (rear transmission seal or driveshaft seal). Check around the edge of the transmission sump for leaks in the sump gasket. Fluid can also leak from the drain and filler bungs.
5. Driveshaft: Check around the rear differential, the drive shaft and rear axle for oil leaks. Leaks in this area can be from an axle seal or from the differential gasket.
3. assess how bad the leak is
Some oil leaks are very small, and it will take a long time for oil residue to build up. Once you have identified the source of the oil leak, you will need to decide if it needs fixing urgently, or if it is a slow leak you may be able to drive the car for a while before it needs repairing. You should always aim to fix an oil leak, even if it is only a small leak. Oil leaks always get worse over time.
To check the severity of the leak, clean the suspected leak location. Assuming there are no other bad symptoms or engine warning lights showing, take the vehicle for a short drive. On return, check the oil leak to see how much more oil has escaped.
4. identify what part needs to be changed
Once you have identified the source and severity of the oil leak, you'll need to figure out what component needs to be changed, and if you are going to pay a mechanic to do the job.
How much does it cost to fix a car oil leak?
Oil leaks an be expensive to fix. Most of the cost will be attributed to labor cost. Some oil leaks involve the removal of a lot of parts to get to the seal or gasket that needs replacing.
Sometimes, if the vehicle is an older, high mileage car you can get away with using a leak sealer. An engine additive leak sealer (or leak stopper) is used to seal small leaks that arise from perished engine rubber seals. To use an engine oil sealant additive, you pour it directly into the engine via the oil filler cap. As you drive the car, the heat from the engine will activate the sealant and it will seal the leak from the inside.
Engine leak seal products are generally safe to use on all engine types, but they may not fix the problem, or may only be a temporary solution. In my opinion you should always try to replace the leaking seal or gasket with a new one if you want a permanent fix.
Here's a table that outlines approximately how much it costs to fix the most common oil leaks in a car. All costs are approximate, and will vary depending on the make, model and age of the vehicle. Labor costs are approximated assuming an average hourly rate of $80 to $100 for a qualified mechanic.
Oil LEak Type
Replacement Part Cost (approximate)
Labor Cost (APPROXIMATE)
1. Oil filler cap leak
$0 (easy to replace yourself)
2 Intake manifold leak
New gasket kit -$40-$60
3. Crankcase ventilation valve leak
4. EGR Valve Oil leak
Gasket ~ $20, EGR ~ $40 -$150
5. Vacuum hose oil leak
Hose/Seal - $30 - $150
6. Front crankshaft oil leak
New seal - $15-$40
7. Rear crankshaft oil leak
New seal - $15-$40
8. Valve cover gasket oil leak
New gasket - $10-$50
9. Oil on spark plugs
New gasket - $10-$50
10. Oil sump leak
New Gasket - $20-$50
11. Oil filter leak
New oil filter and oil -$50-$100
12. Drain bung oil leak
New oil filter, oil and drain bung -$50-$100
13. Transmission input shaft oil leak
New seal - $20-$50
14. Transmission output shaft oil leak
New seal - $30-$60
15. Axle seal oil leak
New seal - $20-$50
16. Differential gasket oil leak
New seal - $5-$20
17. Transmission sump oil leak
New sump gasket - $20-$30