My coolant level seem to go down pretty quickly than it should I feel like. I would fill the reservoir to "MAX" then within a week or so it would be at "MIN" or the reservoir would be just about empty. Also the level tends to go down after a long drive. I checked my hoses for any leaks or cracks, there's none. No leaks or damage to the radiator. No leaks or cracks from the reservoir itself. Car doesn't overheat. However there's no over flow hose to the reservoir. Which leads me to think that evaporation could be the issue maybe due to hot weather since the port where the overflow hose connects on the reservoir is open. I use Prestone (All Vehicles - Ready To Use). I've performed a flush I was wondering if the missing overflow hose could be the problem or is there an issue I'm not noticing ?

It could be vapor loss, try putting some UV dye in the system and use the magic flashlight after a few days. The dye won't lie. If you don't find anything, then it's losing it out the tailpipe from something like a tiny head gasket leak.

I have a similar cooling problem but my 2007 G35 Journey does overheat. 18 months ago both coolant hoses on the back of the engine rotted and had to be replaced (about two months apart). This was done by the dealer. Then it started overheating. A local mechanic replaced the water pump and the thermostat. It still overheated. They thought it was an air pocket. Since then I have been constantly putting coolant in it. I drove to NC last week and it ran fine for 3 hours then the temp gauge maxed out. I pulled over and checked the overflow reservoir. It was full. I let it set for 20 minutes and it sucked the reservoir dry. I filled the reservoir to the "max" level, started it up and it ran at normal temp for about 30 minutes then the temp gauge maxed out again. What is going on? Is this a head gasket leak?

It can't be a big leak if the engine can suck in the contents of the overflow bottle. Large leaks will usually prevent the system from generating any vacuum to suck the bottle down. Since it's erratic, and since you've already had some hose issues, the first thing I'd do is feel the upper and lower hoses when it overheats. The lower should be hot but 20~30F cooler than the upper hose. If the upper is hot but the lower is relatively cold, then the lower hose may be delaminated internally and collapsing from water pump suction. If they're both relatively cold then you have a low coolant or blockage situation. Since it's losing some, first I'd see if the coolant is disappearing outside or inside. Try some UV dye. If there's no blockage and the magic glasses don't reveal anything, then there's a good chance it's a head gasket.