A car engine uses motor oil to lubricate the internal moving parts of the engine
such as crankshaft, rod bearings, pistons and valve train. This oil is
controlled from leaking out of main engine parts by using a series of covers, gaskets and
seals. There are two kinds of oil leaks, pressurized and non-pressurized.
Non-pressurized leaks tend to be less aggressive while pressurized leaks can be
extreme. If an oil leak is not obvious clean the engine with a strong detergent.
Then run the engine for a short time and recheck the engine using a
flashlight. When inspecting for oil leaks start at the top of the engine and
work down as oil will travel downward before collecting into a drip at the bottom of the engine.
What Goes Wrong?
As the engine ages its gasket and seals will become hard and crack due to
heat. This will allow oil to leak out and onto the ground or onto the exhaust system where it is burned
creating smoke from under the hood. These kinds of oil leaks can be smelt from
the air conditioner or heater vents. If the seal on the oil filter or the casing on
the oil pressure sender fail pressurized oil will be forced from the engine
while it runs. These kinds of leaks can drain an engine in a short amount of
How Much Does it Cost?
Oil leak costs will vary depending on the problem which will range from
something simple such as an oil fill cap seal which should cost between $25.00
to $35.00 (US) if you where to take your car into a shop. More involved problems
such as a rear main seal will cost between $800.00 and $1200.00
(US) for a shop to do the repairs. Typically the gaskets or seals will cost
between $10.00 and $80.00 (US).
Let's Get Started
In most cases you will need to
jack the car up and support it on jack stands to get under the car. Use a
flashlight, protective eyewear and gloves.
1. Oil Fill Cap Leak
The oil fill cap is used to add oil to the engine and is usually located on
a valve cover. If this cap becomes loose or seal is broken or has failed to
be reinstalled correctly after adding oil it will cause a leak. Check for
leakage around the cap and tighten replace or reinstall the cap as needed.
2. Oil Filter Leak
The oil filter is used to remove
carbon and other impurities created by the combustion process. This filter is subject to oil pressure
supplied by the oil pump and will leak if the filter is loose or the seal from
the old oil filter is still on the block which can surface well after the
oil change has been done. Use a flashlight check the oil filter for a leak
and remove or tighten the filter and recheck. Wipe the area clean and recheck
the leak after a short time.
3. Oil Pan Drain Plug Leak
A drain plug is used to remove oil
from the engine. This threaded plug uses a sealing washer which tightens flush
against the oil pan and the plug. If the drain plug is loose or the sealing washer is missing or worn
it can cause an oil leak. Check to see if oil is dripping from the plug and then
check its tightness. If the drain plug is loose and will not tighten the threads on the drain plug
are stripped and must be replaced or the oil pan repaired. It is common for a
drain plug to be tight and still leaking due to a failed sealing washer. To
replace the sealing washer will require
draining the oil.
4. Oil Pressure Sensor Leak
The oil pressure sensor is used to send feedback data to the
PCM (powertrain control module) and oil pressure gauge or light
in the instrument cluster. This sensor is subject to oil pressure much like the
oil filter and when failure occurs can leak. This sensor is typically located
near the oil filter and will have a one or two wire connector.
5. Valve Cover Leak
Valve covers are used to encapsulate the valve train and control oil leakage.
This cover is used in conjunction with a gasket which is located between the
cover and the
cylinder head. Due to engine heat
when this gasket ages it can become brittle and crack allowing oil to leak. In other cases the valve cover
can work itself loose which also can cause the aforementioned leak. Sometimes
you can tighten them down but if the cover is already tight then the
cover gasket must be replaced. Brittle valve cover gaskets are a common problem because they are at the upmost part of the engine.
Valve Cover Gasket Leak Video6. Front Crankshaft Main Seal Leak
A seal is used at the front end of the engine which seals the crankshaft where
is protrudes out of the engine block and connects to the front balancer. This
seal is designed to ride against a smooth turning shaft while controlling motor oil.
When this seal leaks, it will typically spray oil on the front of the engine
and down the oil pan. Use a flashlight to confirm the leak and that the
main seal must be replaced.
Front Main Seal Leak Video7. Timing Cover Gasket Leak
A timing cover is designed to control engine oil on timing chain style of
engines. This cover is sealed to the engine block using a gasket which can
leak due to age and heat. This kind of leak can be difficult to find so
sometimes it's best to clean the engine first. This is because the cover is in close
proximity to the front main seal. When replacing the timing cover gasket it
is highly recommended to
replace the front main seal as well.
8. Rear Crankshaft Seal Leak
The rear crankshaft seal does the same job as the front seal but is located at
the rear of the engine. When this seal leaks, it will allow motor oil to leak
into the transmission bell housing and down the oil pan at the rear of the
engine. This seal is more difficult to replace however because the
transmission will need to be removed before the
rear main seal can be replaced.
Rear Main Seal Replacement Video9. Oil Cooler Adapter Leak
Some engines are designed with an engine
oil cooler or adapter that can leak due to seals going bad which stop oil from
leaking between the block and the O ring seal. This seal or gasket will go bad due to heat
and engine vibration which can cause an oil leak. Use a flashlight and look above the oil filter to
confirm the leak which will run down over the oil filter and can fool you into
thinking it is the oil filter that is leaking.
10. Oil Level Sender Leak
Some cars use a oil level sensor is used to provide
feedback data for the PCM and illuminate a oil level warning light to tell the
driver the engine oil level is low. This two wires sensor is located in the side
of the oil pan and is submerged in motor oil. Mounted to the oil pan using an O
ring seal this unit can become hard and leak in which case the oil must be drained
and the O ring and sender replaced.
11. Oil Pan Leak
An oil pan is located at the bottom of the engine and is bolted to the block
using many bolts and is sealed using a gasket. This oil pan is designed to collect oil into
a centralized area allowing the oil pump to re-circulate it back into the engine.
If the pan is damaged or if the gasket fails it can leak oil
around the pan itself. In either case the oil pan must be removed and replaced
if leaking along with the gasket. Depending on the car design this job can be
difficult or quite easy.
12. Intake Manifold Oil Leak
On most V6, V8 and V10 cylinder engine's the intake manifold stretches
between the cylinder head while sealing the engine block from oil leaks at the front and
rear of the manifold on the upper part of the engine. Over time gaskets and
seals age causing them to deteriorate and leak motor
oil. Unfortunately there is no easy fix for this problem and the
intake manifold must be removed and the seals and gasket replaced.
13. Head Gasket Oil Leak
Engines with an overhead cam design have pressurized oil ports in the engine
block that supply oil to the camshaft and lifters. The head gasket is
responsible for sealing oil pressure between the
cylinder head. This kind of leak can be difficult to find because of the
engine's accessories, mainly the exhaust and intake manifolds which are in the
way. There is no easy fix for this problem and the cylinder head will need to be
removed and the gasket replaced.
14. Distributor Oil Leak
Engine designed with an ignition distributor use an O ring seal which is
located on the outside of the distributor housing which control oil between the
housing the engine block. When this seal becomes hard and cracks oil will leak
from the base of the distributor. This problem is not too hard to detect and is
usually on the upper part of the engine are mounted to the cylinder head. To fix
this problem remove the distributor and replace the seal and then reinstall the
Got Any Question?
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