Is your car shaking when you turn off the engine? Don’t panic just yet! While some of the causes may seem alarming, the most common reasons are not that much of a problem and are very simple to fix.
It’s important to note that there will always be a tiny amount of shaking from the car when switching it off. Especially on older vehicles where things have started to wear, not necessarily an issue, just nothing will be as it was when it was new.
4 Causes of the Car Shaking When Turning off the Engine
Of the four causes below, the most likely to be causing you a problem is either a motor/transmission mount or a loose exhaust system. The other two are included because they can happen, but with a suspension or crankshaft problem, you will have more noticeable issues that may make the car undrivable.
Motor mounts or transmission mounts worn
The motor and transmission mounts are the supporting item that attaches the engine and transmission to the car’s chassis, absorbing vibrations. The mounts are usually constructed of rubber set inside a metal casing. The engine or gearbox can’t be bolted directly to the chassis because it would rip out when accelerating due to the forces acting on it, so it requires a mount to allow for some movement. When new, the rubber hardly allows for any movement. But with age, spirited driving, and poor-quality roads, the rubber eventually wears out, cracks, and splits, meaning the motor will move excessively.
If a car shakes when turning off the engine, a worn mount is the most common cause. Because an engine idles at around 1200 RPM and stops immediately after turning it off, you can expect the motor mounts to absorb the small amount of expected movement.
However, when the mounts are worn, you can expect a vicious shake for a second or two when turning the car off. You may also experience problems with worn motor or transmission mounts when accelerating hard, driving at a constant speed, taking your foot off the gas, starting the car, changing gears, and turning it off. It can even be accompanied by knocking noises or the car jumping out of gear if the motor mounts are especially bad.
Loose exhaust
Rubber mounts suspend the exhaust system along the exhaust tunnel. If one of the mount breaks or come off the hangars, the exhaust will be loose, causing it to move around and sometimes knock on the car’s underside, especially when going over bumps.
With a loose exhaust, when you switch off the engine, the sudden stop of the rotating crank will cause the exhaust to shake vigorously. Depending on how the exhaust is sitting, it can vibrate on the car’s underside for a second or two after turning the engine off.
Failing suspension components
Both the shock absorber and coil spring keep the car at a level ride height and absorb bumps in the road. The most common issue for shock absorbers is that they tend to leak their fluid inside when the seals fail with age, so they no longer rebound. Coil springs tend to lose springiness or snap when heavily corroded, meaning the car does not return to ride height.
With a worn suspension component, when turning the car off, the sudden jolt of the engine no longer rotating will cause the weak suspension to rock the car from side to side. This won’t be a specifically forceful shake, but just enough for you to notice. However, it would be surprising if this was the only symptom noticed. With worn suspension components, you should hear knocking noises and feel issues when steering.
Damaged crankshaft
A damaged crankshaft is not a common occurrence and is usually caused by another problem, such as low engine oil. Typically you will hear and feel a bent crankshaft shaking when driving at high speeds, But depending on the severity of the damage, engine vibrations when switching the car off can be all that noticeable.
The crankshaft provides the rotating power produced during combustion to the transmission to rotate the wheels. If the crankshaft is damaged (bent), it can cause the pistons to move unevenly, creating vibrations in the engine.
When the engine is turned off, the uneven movement of the pistons can cause the crankshaft to continue rotating. This can cause the engine to shake or vibrate as the crankshaft slows to a stop which is felt throughout the whole car.
Is It Safe to Drive?
Depending on the cause of the issue, it may be safe to drive for a short period. For example, if the problem of a car shaking when turning off is a worn engine mount, it’s safe to carry on providing it is not causing an issue when driving, i.e., the only time you notice a problem is when turning the car off. However, it still needs to be replaced. Worn motor or transmission mounts cause unnecessary stress on the engine and can cause the vehicle to jump out of gear which will cause further damage.
However, driving with a broken suspension component, loose exhaust, or a damaged crank is unsafe. A broken suspension component can cause the car to snatch to one side when driving in a straight line. The exhaust system can snap, which may cause an accident. Lastly, the engine could shut off or seize up if the crank was to fail. I’m sure you get the picture.
Final Thoughts
A worn motor or transmission mount is the most common cause of a car shaking when switching off the engine. While the vehicle is still driveable, hard acceleration or sudden braking may worsen the problem. Motor mounts are not that expensive or time-consuming to replace, and when driving with a problem that can cause a lot more damage, why not just replace it and be done with it?
