When something is not working properly within a vehicle, one of the first signs of failure is an abnormal sound made by the car. If you hear a squeak from your engine, you need to know what is causing it.
Finding the Noise
Check which criteria have to be met in order to create the sound. Determine if the noise only happens upon start up, or if it is also present in other situations. Also, check to see if the sound happens only when you start the vehicle from a cold temperature, or if it happens on a warm start as well. Have an assistant start the car. Stand in front of the car with the bonnet open. Make sure the car is in neutral with the park brake on, or in parking gear before starting the car. Listen carefully to see if you can pinpoint the general section where the noise is coming from.
Serpentine belts and Alternators
If the sound is an actual "squeak" it will usually come from the alternator region, or the belt that drives it. This the top cause of a squeak when an engine starts. A squeak coming from the alternator can be caused by three primary problems. The alternator belt or serpentine belt can be worn out, the pulley is not working correctly or the internal bearings are worn out. The belt can be serviced by a competent do-it-yourself mechanic. Inspect the belt for cracks and fraying, and see if it is loose. If the belt is damaged, replace it. Pulleys can also be replaced if you can get a replacement part and feel confident taking apart a car.
Any sound that is a "squeak" is usually related to a belt somewhere in the engine. It is a good idea to check all the other belts that you have in your car if you hear this type of noise when you start the engine. While modern cars drive most accessories and the alternator from a single serpentine belt, older cars often used a series of V-belts. In addition, the timing belt can be a cause of a squeak or squeal. A squeaking noise is an indication that a belt is worn, or that the tension applied to it is not set correctly. Adjust the tension on any belt that you feel is squeaking, or replace it if it appears cracked or worn in any way. If cannot isolate the squeak to a belt or alternator you should have a mechanic take a look at your vehicle.
Belt Adjustment and Replacement
You can try to adjust the tension on the belt if it seems loose. Locate the tensioner. It is a small pulley that is spring loaded so that it can apply variable amounts of tension to the belt. (See References 5) If you want to adjust the tension, simply loosen the nut with a ratchet so that you can tighten the belt as required. If you want to remove the belt, you may also want to install a new tensioner in order to help maintain its life longer. A belt with a poor tensioner will wear out quickly. (See References 4) A worn tensioner can also cause the squeal. Install your new tensioner, and route your belt through the pulleys in the same direction that it was previously routed. On a serpentine belt where routing can be complex, be sure you look at the diagram under your hood that shows belt routing. If you cannot find one there, check your owners manual for belt diagrams.