95 Dodge Neon 2.0 DOHC Brakes/Radiator

Hey guys in advance thanks for the help, you guys have always been really great.I have two questions actualy, my stepdad is stumped, and the local auto parts guy, well ill tell ya what he said later, my first problem is my ABS light is on, first time I have ever seen it on. About a week ago I had to brake hard and the abs kicked in allowing the tires to only lock for a split second ( I was brakin on a gravel soaked parking lot ) ever since I have noticed the ABS kicking in when it shouldnt, even under light braking I feel the pedal grind a little bit I guess u could say as the ABS tries to keep the tires from lockin up, but under the conditions, they shouldnt lock up at all. Today after washing my car ( which the local auto parts guy said could cause this ) I noticed the light was on, and also I could brake as hard as I wanted the tired wouldnt lock up, and I couldnt feel the pedal kickin back as it did before ( im pretty sure the pedal kickin back actualy feels natural, like thats the way ABS should do, if its not suppose to do that someone let me know cuz yea thats not good either ). My other problem has been goin on ever since winter started, my radiator cap keeps popping off ( losening itself, actualy twisting itself out of the lock position ) and when this happens the car heats up, when I reach my destination steam is flying everywhere go out and check, and sure enough as always the radiator cap is jus settin there, still where it is suppose to be, still tightened, but it is out of the completely locked position, I bought a new one and to no avail, it does the same thing, here where the auto parts guy comes in, he said that my car needs to burp basicaly, I have a air lock, he said to park the car on a incline like I was driving up a hill, leave the cap off over night, start it in the morning, let it run for a minute or two put the cap back on and it should fix the problem, then I brought up the point that when I start my car with the cap off, usualy anti-freze will spew out of the radiatot like a geiser, then he said tha sounds like a closed thermostat, it wont open for some reason or another, I ran both of those ideas by my stepdad, and he said that neither makes any sence, the burping thing he had never heard of, and he said if it was the thermostat it would happen every day not every 2 or 3 days, ( sometimes longer sometimes shorter but never more than once a day, it pops off I loose antifreze, I let it cool, I fill the radiator back up put the cap on and im good to go for a while) so again thanks guys for any and all help you guys provide, it is really appreciated by all

Chad Eldredge