Step by step guide on how to troubleshoot and repair an automotive engine rattle.
Difficulty Scale: 4 of 10
Begin with the vehicle on flat ground, in park with the emergency brake on, engine
engine relies on oil to supply lubrication to the inner moving parts. If the
oil level is allowed to become low the engine cam followers or lifters will lose
pressure allowing excessive clearance in the valve train causing a rattling noise.
Also, as engine oil levels further degrade the rod, piston and crankshaft bearings
can become damaged allowing clearance producing a knocking sound. Check the engine
oil level and add oil as needed to obtain the proper engine oil level. (Note: If
the oil level is severely low, and the engine is still rattling/knocking after oil
has been added, permanent damage could have occurred and repair or replacement is
required) - Learn more
Step 2 - A belt tensioner is used to hold pressure
against the serpentine belt, when this tensioner fails it can make a rattling noise.
Oil Dip Stick
Step 3 - A mounting bracket is used to support
the various accessories such as the power steering pump, air conditioner compressor,
alternator and air pimp (if equipped). If the bolt becomes loose or the bracket breaks
it can cause a rattling noise, these brackets can be both cast or stamped metal.
Serpentine Belt Tensioner
Step 4 - A timing belt or chain and tensioner is
used to rotate the camshaft(s) that controls intake and exhaust valve operation.
If this belt, chain or tensioner becomes loose or is failing it can cause a rattle
noise that follows engine RPM. To check for this condition remove the timing belt
or chain cover and use a flashlight to check for excess play.
Step 5 - A vehicle equipped with an automatic transmission
utilizes a flex plate
Timing Belt and Tensioner
couple the transmission with the engine, it also supplies the starter with a ring
gear which is used to start the engine. If the flex plate becomes cracked or loose it
too can produce a rattling noise. To check for this condition, remove the flex plate
cover (if equipped) and look for rust colored powder, either at the crankshaft bolts
or the torque converter mounting bolts, also look for obvious cracks or missing/loose
bolts. ( Note: If the transmission is not designed with an inspection cover the
transmission will need to be removed to check the flex plate.)
Step 6 - A harmonic balancer is used to help silence
engine vibration by utilizing a counter balancing weight supported by a rubber ring
which is located at the front of the crankshaft. If this ring becomes dislodged
because the rubber insulator has failed it will allow the outer ring to bounce and
jump on the rotating hub which can produce a rattling noise that may change with engine
speed. To check for this condition remove the serpentine belt and inspect the harmonic
Step 7 - A clutch fan is designed to engage and
disengage as the engine heats up and cools down. If this component fails it can
allow the main shaft of the clutch fan to have excessive clearance, allowing the
main housing to have play while producing a rattling sound. To check for this condition
(engine off) grasp the fan blade and check for excessive movement. Usually this
condition will be accompanied by the engine running hot or overheating, but not
always, it should turn in either direction as well.
Missing Rubber Insulator
Step 8 - When an engine ping occurs, the combustion
processes inside a cylinder has been changed in respect to the control rate of the
combustion process, resulting in an uncontrolled explosion (ping). As a ping occurs
an audible rattling sound is created as the combustion process is more like a flash
instead of a controlled burn. Most engines are equipped with a knock sensor which
controls this condition by signaling the computer to retard the ignition timing,
but if the fuel octane levels are too low, it will cause the engine to ping anyway.
If the problem persists the engine could have excessive carbon build up and a de-carbonization
service is needed.
A rattle or rattling noise can be one of the most frustrating sounds to find
and repair. Rattling sounds can be generated by almost any part of the car from
the engine to the transmission. The cost associated to repair a rattle can vary
between tightening a loose bolt to replacing the a cam follower. Like with any noise,
the first step is locating the region in which the sound is being generated from. If
a rattle is consistent with the engine speed it could be generated by an engine
accessory like an alternator.
Article first published 2016-02-04