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How To Diagnose A Screeching Noise On Your Car Or Truck

Posted by Michael Manning on

Bad Accessory and Drive Belts, Bad Water Pumps and Power Steering Pumps, and More

The most annoying sound is probably a screeching noise coming from the engine. It is a high pitch shrill that can send a chill down your spine. You may have experienced this in your car at some point or you have woken up to the sound of your neighbor’s car shrieking down the street as it warms up. However, you have experienced this sound, one thing is certain, it is not pleasant.

When trying to pinpoint the location and component that is the culprit of all that racket, the pros use a few tips to distinguish what needs to be replaced. If you haven't noticed, there are many accessories under the hood that operate off the running engine. So when you start your car or truck, the rotation of the crankshaft drives several other components such as the alternator, power steering pump, pulleys, tensioner, and water pump.

How do you tell the difference between a screech or a squeal? First, most technicians recommend getting a spray bottle and filling it with plain water—no need to mix it with anything. Then with the engine running and the hood open, spray water on the belt if it is a serpentine belt or on the accessory belts one at a time. If the noise subsides for a minute or so, it is the belt that should be replaced. Accessory belts run your water pump, air conditioning, power steering, and more. They also connect to the alternator pulley.

But if the noise continues after spraying water on the belt(s), the issue is probably with a pulley or tensioner. At this point, you should look at all the accessory-driven components carefully.

Most belt strain happens below 1,000 rpm through operating the alternator, A/C compressor, and power steering pump. Belts can absorb some forces; however, the resulting friction and fluttering will break down the belt sooner or later. When the ribs on a belt wear down and start to bottom out, it begins slipping until it squeals or it breaks.

Belt slippage causes the engine to run hot and belt wear. Not enough tension or a loose belt may come off altogether. Too much tension may overload the belt, putting a strain on the shaft bearings on the water pump, alternator, power steering pump, and air conditioning compressor, possibly leading to premature failures in these components.

Drive belts or V-belts with rubber teeth that are tapered can squeal if they are too loose, cause alternator charging issues, and result in an overheated engine if the belt slips too much. You can check belt tension by pushing down in the middle of its longest point. It has proper tension if you can depress it about half an inch. Any more or less deflection means it is too loose or too tight. A belt that looks cracked or tightening to the appropriate tension does not remedy the squeal; replace it.

Belts that have many visible cracks, or if the depth of the grooves is too shallow, should be replaced right away. Most belt manufacturers recommend inspecting your belts around 60,000 miles and replacing them at around 90,000 miles. An inexpensive belt-wear gauge can be used to check for belt wear. Most auto parts stores have these in stock.

Another issue to watch out for is if the belt and pulleys do not align properly. For the belt to work optimally, the pulleys on the tensioner and drive accessories must all be aligned with the belt to ride in the center, making sure it does not hang over to one side or the other. Alignment is critical with ribbed V-belts. Misalignment can cause squeaking, and it can put more load on the bearing in the pulleys as it rotates when the engine is running.

If a belt breaks, the engine could overheat, and you may lose power steering in systems that have a hydraulic pump. Since belts on many late-model vehicles drive the water pump, it is critical to watch for signs of wear or unusual noises coming from the drive system. If the belt cannot turn the water pump, the engine will overheat quickly. You may be able to limp home if you are close to your destination (within a mile or two), but anything further may require a tow.

Other issues that cause squeaks, squeals, and screeches include metal-to-metal contact with rotating parts such as engine bearings and crankshaft with no oil film protection, camshaft bearing failure. Worn connecting rods can make a knocking sound, and worn tensioners or timing chain guides can sound like a chain is slapping or loose (because it probably is loose).

Most belt failures result from one of the components in the drive system seizing up, such as when a bearing in the water pump fails. Shortly before it seizes, there are usually warning signs that sound like a chirp or a belt squeak. This is because there is more load on the system, and the belt is probably starting to slip or stretch. Frayed edges can also be a tell-tale sign that something is wrong with a pulley. An alternator that is beginning to fail may also put added strain on the belt system, but it may also pop up an engine diagnostic trouble code (DTC) due to the lack of battery charging.

Power steering pumps that run off of a belt use hydraulic fluid to pump through the steering rack on one side or the other to move the wheels right or left. A failing power steering pump can make a whining sound if it is low on fluid or the pump itself is starting to seize. Eventually, it will apply more load than the belt can handle and breaks the belt or the pulley, rendering your steering impossible to turn.

With all the noises under the hood, it can be challenging to know which ones are bad or good and what needs immediate attention. If you haven't heard a noise before, pay attention, your car is trying to tell you something.

When it comes to DIY Mechanics, Partsology has all the engine parts you need to fix a squealing serpentine belt or rebuild an engine, from idler pulleys and water pumps to engine rebuild kits. If your car or truck starts to screech when you start it and you need quality parts to fix it without breaking the bank, shop now or contact us at (844) 800-6866 today.


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