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I have a 1937 115C Sport Coupe which I have inherited. It had been stored in a garage in Connecticut for many years and run infrequently. I had it shipped to me in Florida about a year ago and am now just picking away at regular maintenance. I want to change the antifreeze and replace it because it has not been done for several years. The fluid in there is still green and no rust floating around that I can see. My question is, what kind of a mixture should I put in since it obviously won't be freezing any time soon but it will face the heat of summer time Florida when it does get driven.

I will probably have many maintenance questions as they come up so thank you for any insight.

Use a 50/50 mixture of coolant and water. If the car does not run it's going to be hard getting the solution into the engine and heater core (if it has a heater core). Take the thermostat outlet off remove thermostat and pour the coolant into the top of the block then replace everything, also now might be the time to change all the cooling hoses and the thermostat and gasket so you don't need to add more coolant if you need to change any of these items later. Hope this helps.....that's what this forum is all about. Welcome.
Your service and other factory literature are available here on this site. Look at the left margin and see all the offerings.

I would also add to make sure you don't buy the antifreeze for modern cars, as some of the additives are significantly DIFFERENT.

I had three Packards when living in Austin, Texas: 115C, 2122 and 5542. The winter temps would infrequently get to 32F or a bit lower. The summer temps were another matter, frequently getting to 100F and above. I used a 25% mixture of permanent type (green) antifreeze and de-ionized water in the cooling systems. This mixture was enough to protect from winter cold, and it also gave me good summer cooling since water is a better transfer of heat than antifreeze. I could have run water only with an anti-rust inhibitor in the summer, but chose to use a year-long coolant. A 50-50 mixture will protect way down to -34F, way below what you will see in Florida. My 2 cents...

the glycol mixture raises the boiling point as well as depresses the freezing point

While you have it drained, you might want to back flush it while your at it. Old coolant can become very corrosive.
Wes

I'd follow along with JW's line of thought. Water has better heat transfer properties than ethylene or propylene glycol so in order to maximize your cooling system efficiency for the best cooling, you only want enough antifreeze present for your expected lowest temperatures, plus a little extra for a safety margin. If the amount is very small or none, then add a can of corrosion inhibitor.

Thanks for the info guys.

In reply to packardguy53, the car does run and is registered, even though, since I've gotten it to Florida with it's horrible drivers and the fact that my garage is located in a pretty busy section of town, I haven't taken it out of the garage. I'm building up to it. LOL

Also, to Gar's point about not using coolant designed for modern cars, what brand would you suggest? I would have just gone to Advanced Auto and gotten whatever was on sale. Glad I didn't.

The boiling point of a typical northern 50/50 mix is 225 F vs 212 F for water (without pressurizing system). But the heat capacity is about 15% less than water - in other words it takes 15% less heat to increase the temp the same amount. So the previous posters advice about using a little glycol for its anticorrosive additives, or adding them separately, is sound. None of these will solve problems related to transfer of heat to the cooling air.