My 500 quest (2004) has decided to sometimes start and sometimes not. The battery must be full since the lights are good... and once when it didn't start, I shook things around and then it started.

Another thing I've noticed is that this is happening after an oil change... and the oil light is turned on... maybe I have too much oil?? (it just passed the line by 4mm)

what do you think?

 

Don't always assume a battery is ok unless you have it load tested. If it checks out ok then move on to other areas such as possible shorts or possible corrosion on connections.That's also where the service manual can help as the oil light may be triggered after an oil change and may need to be reset.

 

I checked the service manual for that oil light... and I'm charging the battery... it's not even turning slightly and I can tell plenty of juice is getting to the starter.
I think my starter is finished... I wish I knew of a quick thempray fix... like a pull cord would be nice

 

Make sure connections at the solenoid and starter are ok and no corrosion.

3) Load Test the Battery

Your local automotive shop is more than able to load test your battery for you. But it's quite easy to do at home. All you need is a digital voltmeter. For any load test to be accurate, the battery must be fully charged. Let's use a motorcycle battery for an example. Remove the seat and expose the battery in your bike so that you have access to the terminals. Do not disconnect the battery because you will attempt to start the bike. Hold the prongs of your voltmeter to the correct terminals on the battery. Now push the starter button and watch what the voltage drops to. It doesn't matter if the bike starts or not, what you're looking for is a voltage reading.

DC Voltage in healthy 12 volt motorcycle battery should maintain a range from 9.5 - 10.5 volts under the load for a good 30 seconds straight. If the battery begins to hold and then steadily drops in voltage, there is a problem. If the voltage instantly drops to 0 volts, that is also a problem. We call this the open cell. On a new battery, this can be a result of manufacturing flaws, but it also may be caused by sulfate crystal buildup. Under the intense heat of the load, one or more of the weld pieces connecting the cells is coming loose and separating. This will cut the current, and voltage will drop. When the battery cools off, the pieces will touch, barely giving a complete connection. This gives you a false voltage reading. Batteries with open cells may read fully charged in idle, but they fail under a load test every time. Once a battery reaches this point, there is no going back. The best thing to do is recycle the thing.