If you’ve ever heard a diesel engine at idle before, you might have thought something was wrong with it because of the sound it makes. Diesel engines have a distinct clattering quality to the sound they make, which is caused by the way a diesel engine ignites fuel. Gas engines ignite fuel differently, so they don’t make this kind of noise.
If the engine in your gas car does sound kind of like a diesel, however, it means that something is definitely wrong with it. The source of the problem could be a number of things, including an incorrect air/fuel ratio, a bad belt tensioner, or bad spark plugs, among other things.
In this article, we’ll be going over several issues that can cause your gas car to sound like a diesel, and explain how you can deal with these issues. By no means is this a totally comprehensive list of everything that can cause this problem, but we will be covering some of the more common issues here.
Incorrect Air/Fuel Ratio
For a gas car to run smoothly, the ratio of the air/fuel mixture that enters the combustion chamber needs to be just right at any given time. Usually, it’s up to the various sensors in the car to determine how much fuel to add to the mixture based on the position of the gas pedal and how much air is in the engine.
If these sensors stop working, however, they can easily throw off the ratio of your air/fuel mixture. This can cause your engine to run either lean or rich, although if you’re hearing a clattering or knocking sound, it’s far more likely that your engine is running lean.
If your engine is running lean, the most common causes are a bad oxygen sensor, a bad MAP (manifold absolute pressure) sensor, or a bad MAF (mass air flow) sensor. You should inspect these parts first before examining any other parts.
Faulty Belt Tensioner
If you’re lucky, the source of your problem might not have anything to do with the engine itself; it might simply be a case of a bad belt tensioner. As you probably know, your engine contains two main belts: the serpentine belt, which connects to the crankshaft and powers the car’s various accessories, and the timing belt, which synchronizes the rotation of the camshaft and crankshaft.
To prevent the belts from slipping, there needs to be a certain amount of tension placed on them, which is where the belt tensioners come in. If one or more of the belt tensioners fails, then the belt will have a lot more play to it, which can cause a knocking or rattling sound when the belt starts turning at speed.
The same thing can also happen if one of the accessory pulleys becomes bent out of shape, or if the belt itself becomes stretched out. Fortunately, if you’re thinking of replacing one of your car’s belts, replacement parts are usually pretty cheap.
Bad Spark Plugs
The spark plugs are, of course, the component of your car’s engine that ignites the air/fuel mixture at the right time. As spark plugs get older, however, they start to wear down and become less effective at combusting the air/fuel mixture correctly. This incomplete combustion can add a clattery quality to your engine’s sound.
To solve this problem, you just need to replace any spark plugs that are on their way out. You should look for any spark plugs that have a lot of carbon buildup on them and replace those, but you should also make it a point to replace your spark plugs every 30,000 miles or so.
Gasoline Octane Rating Is Too Low
This probably isn’t the issue if you have an average commuter car, since most cars these days are designed to accept gasoline with the lowest octane rating. However, if your car has an engine intended more for sports driving, you might run into issues if you use fuel with too low of an octane rating.
Basically, the higher a fuel’s octane rating is, the more it can be compressed before it combusts. High-performance engines usually have a pretty high compression ratio, so they naturally need a very compressible fuel. If they get a low-octane fuel instead, this can lead to premature combustion and cause a knocking/clattering sound.
If you’re not sure what kind of fuel your car needs, you can find this out in your owner’s manual.
Worn Rod Bearings
The pistons in your engine are connected to the crankshaft via the connecting rods. At the place where each connecting rod meets the piston, there is a rod bearing. The rod bearings ensure that the piston moves smoothly up and down within the cylinder.
If the bearings start to wear out, however, then the pistons will start knocking around inside the cylinders. If you find that the source of the noise is worn-out bearings, you should replace them as soon as possible; aside from being noisy, worn rod bearings can eventually damage your connecting rods.
Carbon Deposits
As the air/fuel mixture is ignited inside your engine, it leaves behind little bits of burnt carbon on the pistons and the inside of the combustion chambers. As this carbon accumulates, it starts to mess with the compression because it changes the volume of free space inside the cylinders.
Modern gas comes with a bunch of additives intended to remove carbon deposits from burnt fuel, but some of those carbon deposits still make it through. Fortunately, you can solve this issue by cleaning your internal engine components with a wire brush and a solvent for removing carbon deposits.
Faulty Valve Lifters
The valve lifters in your car’s engine are hydraulically actuated, and ensure that the valves in your engine open and close when they’re supposed to. If one of these lifters gets stuck, this can be what causes your engine to sound a bit rattly.
If one of your valve lifters is stuck, you can solve the problem by using a fuel system cleaner, by changing your oil, or by physically removing the lifter from the engine and cleaning it.