Coolant light stays on after coolant was added

Your overflow tank(aka coolant recovery reservoir) is low on coolant. The coolant expands when warm and raises the level in the tank, which turns off your light. Top off the reservoir (when cool) to the "Full Cold" line. If you have to keep adding on a regular basis, then you have a leak somewhere in your cooling system, could even be the reservoir itself.

make sure you are still full it could also be air in the system if your car is getting temp is getting hotter than usual it is probably air in the system it could also be a stuck sensor.

Make sure there is no air in the system, take the radiator cap off and let the engine idle for half an hour, as the air comes out the coolant will go low, ad more coolant and then close the cap on also make sure the resevour bottle is at its mark.

The switch in the coolant tank that turns the light on can stick due to contamination from old coolant.Replace this switch,or leave it disconnected.If your battery drains overnight,there is likely a draw,possibly trunk ot glove box light on.If the problem started when the alternator was replaced,it could be a shorted diode in the alternator.

most cars and trucks have a censor on radiator or fill tank,ck the coolant level and if it is full then censor should turn lights off if it is low fill with water to full line and light should turn off

I've had this happen on my Boxster as well. Couple of things to look (and smell) for:
Leaks, look around the water pump under the engine, around of the rear firewall (between the trunk and the engine compartment) and the trunk. You can usally smell the coolant. The coolant tanks are notorious for cracking and leaking.

Air in the coolant system. The coolant has to run the length of the car from the trunk to the engine to the radiators in front of the front wheels and back again. If there is air in the system it will cause the car to run hot. A mechanic can bleed the system with a vacuum or you can do it the more tedious but cheaper way:
Turn on the heat on full
Add coolant to the full mark on the tank
Bring the car (engine) up to temperature by driving or idling. You want the thermostat to fully open.
Let the coolant come down in temperature in order to open the cap to the coolant tank without hurting yourself and fill the coolant tank to the full mark.
Go through this process repeatly unitl the coolant tank does not need refilling. There are several articles on the Boxster forums.

Your sensor for the coolant level is bad. It happens hope this helps

Did you add the fluid to the Radiator or the Overflow container. The radiator should be full and the overflow container should have a mark on it for full. Make sure both are full. If they are then you most likely have a bad sensor that you will need to locate and replace.

Your coolant is above the min and below the max line when your car is cold right? If so, it appears that the sensor attached to the reservoir tank may have gone bad...

i have a 2003 vw beetle turbo. The oil light blinks even after a recent oil change.