Auto Repair Advice by Professional Automotive Experts
Troubleshooting
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Why Does My Engine
Leak Oil?
Why Does My Engine Leak Oil?
Introduction
Any engine oil leak is not normal, when you notice oil underneath your car it
means an engine oil leak has developed. Inside the engine there are two states
of oil, pressurized and non-pressurized. Oil leaks that are not pressurized tend
to be less aggressive. Oil that is pressurized will leak more when the engine is
running, while non-pressurized oil leaks tend to be steadier. Always check the
engine oil level before you start, and if your engine is dirty it is a good idea
to clean the engine before so you can locate the exact source of the leak. Use a
good degreaser like 409 or Fantastic etc. Always clean an engine cold to avoid
steam. Steam is the cause of many electrical problems after an engine has been
cleaned. Try to inspect the engine yourself to get an idea of where the oil is
coming from. This will help you estimate the repair if you are going to have the
oil leak repaired. Oil leak repairs can vary greatly so it's best to get a
second opinion if the repair estimate is extreme. Use a flash light to pin point
the source of the leak, then formulate a plan to repair it. When inspecting for
engine an oil leak always start at the top of the engine and work your way down.
We have listed common causes for oil leaks below.
Car Repair Guide - READ COMPLETELY BEFORE BEGINNING!
- Step 1 - The engine oil fill is used as a port to add
oil to the engine. If this cap is left off it will cause engine oil to be
expelled from the port when the engine is running. With the engine off lift
the hood and located the engine oil fill port. Once this port has been
located check the cap and its condition. If the cap is missing replace the
oil fill cap with a new unit. If the oil cap is leaking remove the cap and
replace the cap seal. Clean the area and recheck for the leak after a short
operation period. Even though the engine oil is not under pressure internal
engine pressure can force oil out of this port.
Engine Oil Fill Port
- Step 2 - The engine oil filter is used to filter engine
oil of carbon and other by products created by the engine and the combustion
process. This oil filter is in direct connection with the engine's oil pump
and is subject to high oil pressure. One of three things generally occurs
when oil leaks from this area. First and most common is the oil filter is
not installed properly. The filter either is not tight enough or the old oil
filter gasket was not removed. When there are two gaskets or the filter is
not tight enough the oil filter cannot seal. These problems can surface long
after the filter replacement. Finally the oil filter itself is leaking, but
this doesn't happen very often.
Change Motor Oil and Oil Filter
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Step 3 - The oil drain plug is used to remove the oil from
the engine when a service is performed. The drain plug is a threaded flanged
plug that uses a sealing washer to contact the oil pan. This seal is what
keeps the engine oil from leaking out. If the drain plug is loose or the
sealing washer is missing or worn it can cause an oil leak. This plug is
located at the bottom portion of the engine oil pan. To check your oil drain plug gasket attach a wrench to oil drain plug and try
to turn it counter clockwise. If the plug is tight but oil is still leaking
the washer has failed and must be replaced. If the drain plug is loose and
will not tighten the threads on the drain plug or inside the oil pan have
failed and must be replaced or repaired to fix the problem.
Typical Oil Drain Plug Configuration (FWD front wheel drive)
- Step 4 - The valve train inside the engine is covered by
valve covers, these covers are sealed to the cylinder head with a valve
cover gasket. When this gasket ages it can become brittle and crack
allowing engine oil to leak out. Sometimes a valve cover can become loose
over time. Fit a socket or wrench over the valve cover hold down nuts or
bolts. Try to rotate the socket or wrench counter clockwise, it should be
snug. If the mounting bolts or nuts are loose tighten and recheck. If the
hold down bolts or nuts are tight and the valve cover is still leaking the gasket
needs to be replaced.
- Step 5 - (This step is for V12, V10, V8 or V6 engines
only) The intake manifold is mounted to the cylinders
heads with a seal between the engine block and intake manifold. These seals
are located at the front and rear of the intake manifold. Over time theses
seals can age causing them to deteriorate and leak motor oil.
Unfortunately there is no easy fix for this condition, the intake manifold
must be removed and the seals replaced to repair this problem.
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Step 6 -
An engine is
designed with a number of shaft seals depending on the type of engine it is.
A timing belt style of engine has more shaft seals than a non-timing belt
engine such as cam and balance shafts. All engines have front and rear
crankshaft seals. These seals are designed to ride against a turning shaft
without allowing oil to pass through the seal. Engine heat can cause these
seals to become brittle; as a result the rubber lip contained in the seal
will fail allowing oil to exit the engine. Depending on the location of the
seal, replacement procedures can vary from removing the transmission to
disassembly of the engine front
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Step 7 - Timing chain style engines have timing chain
covers that are sealed to the engine block using a gasket. With time this
gasket can become weak allowing engine oil to leak. If after inspection this
is the case with your engine, the only remedy is to disassemble and remove the
timing chain cover to replace the gasket.
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Step 8 - Some engines are designed with an engine oil
adapter that seals to the block with a gasket or "O" ring seal. This adapter
is what the oil filter screws onto. Heat can cause the seal or gasket to
fail, once a failure has occurred replacement of the seal or gasket is required.
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Step 9 - Most engines are equipped with a distributor
drive port where the distributor or sealing plug is mounted. If the "O" ring
seal fails it will allow engine oil to leak out under pressure. If this is your engines oil
leak the "O" ring seal must be replaced to repair the problem.
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Step 10 -
The engine oil pan
is used to collect the engine oil into a centralized area so the engine oil
pump can re-circulate it back into the engine. This pan is bolted to the
bottom of the engine and uses a gasket to seal it to the engine block.
If the oil pan gasket fails it can allow oil to leak from the engine. To
repair this problem the oil pan must be removed and the gasket replaced.
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Step 11 - Overhead cam designed engines have oil ports
in the engine block that connect to the cylinder head. Oil is pumped under
pressure into the cylinder head to lubricate the camshaft and other
valvetrain components. If the head gasket on these engines fail it can cause
this pressurized oil to leak out from between the engine block and cylinder
head. If this is the case with your engine the head gasket must be replaced
to repair the problem.
Note: Few engines are equipped with engine oil cooler that can leak. This
engine oil cooler should be inspected when checking for an oil leak.
WARNING! Always have the vehicle under inspection on level
ground, in park with the emergency brake on. Always wear protective eyewear, gloves
and necessary clothing before inspection or work begins. Never crank an engine over
when anyone is near the battery or engine. Always have an operational fire extinguisher
close by, obey all first aid instructions in the event of an injury. Never stand
in front or behind a vehicle when starting or running. When engine is cranked over
keep hands and clothing away from rotating components. Anyone with a heart pacemaker
should not perform these tests.
Troubleshooting
/
Why Does My Engine
Leak Oil?
Additional Resources
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Oil Leaks Questions and Answers
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