Why Does My Car Rattle On Start Up?


Why does my car make a rattling noise when started?

Rattling on cold start up is usually an indication of a timing chain issue. Timing chains synchronize the crankshaft and camshafts so they rotate at the proper time for the engine to run properly. The example vehicle we have today has 2 camshafts per cylinder head one for the intake stroke and one for the exhaust stroke totaling in four camshafts. The camshafts are connected to the crankshaft with a timing chain. There are multiple other components that are also used like timing chain tensioners and timing chain guides to help keep the chain tracking normally and remaining tight at all times. The crankshaft and camshafts sprockets are designed much like the sprockets on a chain driven bicycle with little points that fall into the chain one at a time and spin around. As the crank shaft rotates the timing chain is pulled with the sprockets in turn also rotating the camshaft sprockets in perfect time.  

What causes a timing chain to make noise?

The constant metal on metal contact of the timing chain on the crankshaft and camshaft sprockets will cause slight wear over time. Engine oil is used to lubricate these items and reduce the wear that is caused, but wear is still inevitable. As the timing chain and sprockets wear a chain stretch condition is created, meaning the tension on the timing chain is not what it should be. When there is insufficient tension on the timing chain it is allowed to bounce around and cause a rattling noise. Mostly noticeable during cold start ups when engine oil pressure is low and oil temperatures are cold. The noise will usually become less when engine temperature and oil temperature reaches normal operating conditions.

How do I get the most out of my timing chain?

The most common contributor to timing chain stretch is lack of maintenance. Going too long in between oil changes and not using the right oil for a vehicle will cause a timing chain to wear out prematurely. Oil is not only used to lubricate the moving parts of an engine but also to catch debris. Regular oil changes with the proper oil is very important for timing chain life.

At Dickerson Automotive we use high quality oil, and oil filters in order to ensure proper lubrication and to maintain clean oil for as long as possible. If you have a strange rattling noise don’t hesitate to give us a call!