It's 60 degrees and sunny here today, so I thought I would check on the Daytona in storage. To my surprise all of the pink anti-freeze coolant was gone from the reservoir. I have twins and just the strbrd motor did it. What has gone wrong here? Is this a big problem? Any input would be great...

Closed cooling system has a leak???

Where would be the most obvious place to check for the leak?

leak somewhere ....could be a blown headgasket .....has it got hot ? More likely a small leak somewere ..

Last season the motor got hot a few times due to debris in the oil cooler restricting water flow to port exhaust manifold. The guardian system shut it down though before any damage. Cleaned it out then it ran fine and didn't notice any leaks until just now.

See if the oil level has gone over the "Full" mark.

Yikes !!!

Hello i have the same problem ,living up north here in Chicago i was freaked out it might be the engine block ......Heres the GOOD news
With the 496 closed cooling on the ride side of the engine where the air pump system is
you will see on the Heat exchanger a hose fitting ( cross-over) the grommet /gasket is the cause of your leak The leak is caused by the rubber grommet expanding and shrinking with temperature change ,You need to have it replaced this is a unofficial mercury Service bulletin . Some people have reported that re-filling it back up in the spring ,has not reproduced the leak and there find for the summer /I do not recommend this action
Get it corrected while your out of the water

If your heat exchanger is cracked..the antifreeze will disappear out the back of the boat and be replaced by lake water...It will never overheat..

This is probably almost definitely the problem. Both my 496's on my last boat did this and it is a Plastic/rubber grommit that is described above. Mercury covered it and they know of the issue.