okay so i have a 95 626 v6 and one day im on the highway with it and it overheated so pulled over and my dad came. said i had no coolant. so he put some in and i looked under my car and it was all leaking outon the passenger side.
so i had it towed to my dads mechanic. he said it was two hoses so he replaced them. he drove it around the block and my temp guage didnt go past half way. ok cool ! so i start driving it and 10 minutes later the gauge is at hot ! couldnt understand what was going on but a bunch of people told me that i prob needed to replace my thermostat. so i went and bought one and my friends dad put it in for me the next day. he said he drove it around the block too and my temp gauge didnt go past half and i had heat again. ok problem solved. NOT ! i tried to drive home and my guage kept fluxuating between midway and hot for like 10 minutes but was still blowing out heat. then all of a sudden it goes into the lil red box past the hot line and starts blowing cold air out at me. tried again this morning and it did the same thing. anyways .. i was just wondering if anybody had a good idea of why this is happening ?!

 

I can give you things to check. First check your raidiator fans for proper operation. Both should run with the A/C on at idle. Check the coolant level and top it off. Let the engine idle with the A/C off. ( you already checked the fans right?). Pull the cap off the coolant tank and watch for bubbles. Give the system time to purge the air out of it if it was low. Watch your temp gauge too and the radiator fan should kick in eventually. Rev the engine a few times while watching inside the coolant tank. If it produces bubbles you probably have a blown head gasket. Waterpumps are notorious for leaking when you park the car overnight then they seal up when warmed up. Look for a puddle under the car after it sits a few hours.
One other check is pulling the oil fill cap and looking at the cap. Does it look like chocolate milk or black oil? milk is bad. It means there is water mixed with the oil.