Engine Turns Over but wont start
When the engine is starting the engine turns over but won't start, the possible reason why the car wont start is that the current flow to the starter is restricted, other reason is a weak battery, bad starter, a partially frozen electrolytes or a bad electrical connection.
Possible cause why the Engine turns over slowly while starting
Restricted Flow of Current to the Starter
This kind of problem is usually involving battery, now determine if the car has a battery related problem by doing a simple test. Turn on the ignition key to start the engine then observed if the headlight brightness changes. If the engine headlights changes brightness while the engine is starting then it is a battery related problem.
When the engine turns over slowly and will not start and while doing the simple test the head light brightness changes while the engine is trying to start then it more likely that the current is not flowing into the starter.
Open the hood of the car and locate the battery. Check the battery terminal if there is a cruddy like substance this means that the terminal is corroded. This causes the current not to flow into the starter.
To fix the problem you need to remove the corrosion on the battery terminal.
Apply some baking soda and water on the terminal to help dissolve the corrosion then brush the terminal using a wire brush. After the terminal is cleaned, apply some petroleum jelly on the terminal to help prevent terminals from corroding in the future.
After doing a simple test mentioned above and after inspection of the battery terminals, the terminals is free from corrosion then the problem is a weak battery. When a battery is weak the battery cannot provide enough current to start the engine and will only turns over during starting.
Check the liquid level of the battery, the liquid must cover the top of the plates inside the battery. Add some distilled water on the battery if the fluid level is low. If the problem still occurs then replace the battery with new one.
Try to start the engine and observe if there is an unusual sound like grinding or growling sound coming from the engine. If there is grinding or growling sound then a problem is a bad starter. If the starter is bad the engine will not crank fast enough to start the engine.
To fix the problem you need to replace the starter. Consider using a rebuilt starter since it is much cheaper than the new starter.
Partially Frozen Battery ElectrolytesIf the problem happens only when the temperature is very cold then the problem is a frozen battery electrolytes. When the electrolytes of the battery is frozen it causes the battery to lose much of its power, battery with not much power will not crank the engine.
In this case just wait for the temperature to get warm and let the battery electrolytes to defrost before starting the engine. Also if you are driving mostly on cold area use a battery with a good cold cranking rating because this kind of battery is reliable in cold weather.
Bad Electrical Connection
When the battery and the starter is in good condition then possible problem is a bad electrical connection. Usually a bad electrical connection between the starter and the battery happens this will result in the starter not getting enough power to turn the engine to make the engine start.
Look at the electrical connection between the battery and the starter, check if there is a loose connection in between or bring the car to a reputable car shop and ask the mechanic to inspect the connection between starter and battery.