First off I’ll give a little background, I bought my 1999 Jeep XJ almost 4 years ago and it always ran fine and the coolant was always at I believe it’s 220. One day I noticed the Jeep getting hotter so I checked the fluid level and there was no fluid in it, so I filled it up and checked for leaks and there were no leaks anywhere in the coolant system. This has now been a reoccurring problem I have been having where I notice the Jeep is getting hot and I check the fluid later on and there is none in the radiator or reservoir. I have also changed my oil a couple times since then and it looked like oil and smelled like oil, so I’m not sure where it is all going, is it burning the coolant? It also makes a whine noise from the engine bay when running from time to time, I’m not sure if that has anything to do with it. Any help will be good, and like I said I’ve looked for leaks time and time again because I figure there had to be one and there is not a leak I can find. Thanks in advance.

Is it possible it's boiling out of the overflow after you shut off the car when it is hot outside but you haven't noticed?

If the oil looks and smells like oil, and there are no signs of leakage, it could be a faulty radiator cap. A loss of pressure allows coolant to escape, and then evaporate. It can go undetected. As emx72 posted, it could be the recovery. The plastic gets brittle with age, too. A leaking water pump could be it as well. Find the weep hole underneath and look for any signs of coolant. Fresh will be obvious, but when coolant evaporates, it leaves a white residue, usually. It can be hard to see if it is. Or it could be a blown head gasket. A head gasket can fail in different ways. The coolant can find its way into the oil, or the cylinders. or both. When it gets into the cylinder, it gets passed with the exhaust. The white smoke could be exhaust, but can be mixed with coolant. Does the exhaust smell sweet? Check your plug. Coolant will keep them looking new. I would check the floor under the heater core as well, just because. Coolant can leak from anywhere. A loose hose clamp, even.

Not sure what that whine could be. Like coolant, it could be anything. A pulley, an accessory, a diff, transmission, etc..

It could be possible to be boiling out of the overflow, but unlikely because the lid is still fixed on the overflow when I open the hood. It does it as well when its cold out and there are no signs of it boiling out. I also put on a new radiator cap because that's what I thought was the issue but it is still doing it. I'll have to investigate with smelling the exhaust and checking the plugs to see if there is anything. I wasn't sure if it was burning the coolant in some way or another. Thanks for your suggestions, I'll take a look hereafter I am done at work.

by far the best way to find a leak in the cooling system is to pressurise it, thats how I found an invisible leak on my inside radiator seam, the leak never dripped, or left a visible mark

if no leak is found, and you want to be sure, send your oil for analysis, which is about $30, and will reveal the presence of glycol coolant in the oil

Do a test for exhaust gasses in the coolant. Checking the oil via dipstick is NOT an adequate test. Water in the oil doesn't always happen with a blown head gasket or cracked head, and even if it;s there, it might not show up on the dipstick.