Would a loose overflow tank cap cause the coolant to come out?

get a pressure test on radiator via a radiator cap that has a pressure gauge with the engine running . The head gasket is probably blown on the engine and this can cause exhaust pressure to go into the cooling system and create this symptom you are experiencing.
you may also have more expensive problems like a warped head or cracked head . $$$$$ - remachining or welding and remachining of engine head and a blown gasket .

is the cooling fan coming on when it is hot?

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If the thermostat is not opening, the engine will keep getting hotter as you drive. You could be low on coolant and have air pockets in the system which would cause the temp gauge to not be accurate. Is the radiator fan coming on when the tank is boiling ?

a flashing check engine light (CEL) is a warning to stop driving-one that is on steady (not blinking) means something is wrong, but blinking is BAD-make sure it is completely cooled down, and fill the overflow/surge tank, start it up (use 50/50 antifreeze) and let it idle until the engine temp is all the way up-this can take 10-15 minutes, make sure the heater is on high temp setting and the fan is on-look at the temp gauge if it has one to see if it looks normal. If all looks good, fill the tank to the FULL mark (or a hair above it) and put the tank cap on tight. Drive the car for about 10 minutes, and pay attention to the temp gauge-if it looks good, and the engine is alright, the CEL probably with either not light or will go off by itself.

It is possible you did damage driving it with a flashing CEL, however-if so look for leaks, smoke out of the exhaust, poor running/performance, or more ominous signs of trouble like air bubbles in the overflow tank, oil in the antifreeze of antifreeze in the oil-aluminum engines do NOT tolerate overheating, if you ever see a high temp gauge and/or a flashing CEL-STOP and get it checked out, you will save yourself a lot of money being prudent.

CHECK COOLANT FAN FUSES AND RELAYS. CHECK COOLANT LEVEL.MAKE SURE ITS NOT TOO LOW BECAUSE IF COOLANT TOO LOW . BY NO COOLANT AROUND OR COOLANT SENSOR NOT SUBMERGED IN COOLANT COOLING FANS WONT TURN ON.MAKE SURE YOU HAVE 50/50 ANTIFREEZE AND WATER. CHECK FOR CLAPSE RADIATOR HOSES.CHECK RADIATOR HOSE AT WATER PUMP.IF HOSE LOOK CLAPSE REPLACE IT AND BLEED COOLANT SYSTEM.IF EVERY THING HAS BEEN DONE YOU NEED ENGINE BLOCK FLUSHED OUT.HEATER CORE ALSO COULD BE STOPPED UP.A VERY HIGH MILEAGE ENGINE WILL OVER HEAT.OLD ENGINE LOSES COMPRESSION AND HORSE POWER.PUTTING MORE LOAD ON THE OLD ENGINE WILL MAKE IT OVER HEAT.IF COOLANT LEVEL IS LOW.BLEED COOLANT SYSTEM.START THE ENGINE LET IT IDLE FEW MINUTES WATCH THE COOLANT TEMPERATURE GAUGE.WHEN TEMPERATURE START RISING.TURN OFF THE ENGINE LET IT SET FOR 20 MINUTES.TAKE A LARGE RAG PLACE OVER RADIATOR CAP ON COOLANT EXPANSION TANK SLOWLY OPEN RADIATOR CAP JUST A LITTLE TO RELEASE A LITTLE PRESSURE AT A TIME.DONT OPEN CAP RAPIDLY OR YOU WILL GET SCALDED.ONCE THE RADIATOR CAP REMOVED.IF COOLANT LOW ADD MORE COOLANT IN THE THE COOLANT EXPANSION UNTIL YOU GET TO THE COLD MARK.REPEAT THIS PROCEDURE START ENGINE LET IT RUN UNTIL TEMP GAUGE START CLIMBING A BIT DONT LET CAR RUN TO OVER HEAT JUST IDLE UNTIL TEMP JUST START TO RISE.THEN YOU TURN OFF ENGINE. WAIT 20 MINUTES.THEN USE LARGE RAG OPEN RADIATOR CAP LITTLE AT A TIME. DO THIS PROCEDURE UNTIL THE COOLANT IN THE EXPANSION TANK STOP DROPPING. THEN ALL THE AIR IS BLEED OUT THE COOLANT.WHEN COOLANT LEVEL STOP DROPPING, WHEN YOU DRIVE CAR AROUND.AND TURN OFF ENGINE.WHEN ENGINE OFF CAR SET FOR A WHILE KEEP CHECK ON THE COOLANT LEVEL IN COOLANT EXPANSION TANK. THE COOLANT LEVEL SHOULD BE AT THE COLD MARK IN THE EXPANSION TANK.MAKE SURE COOLANT IS IN THE EXPANSION TANK.IF NOT AIR WILL DRAW IN COOLANT SYSTEM. CAUSING ENGINE TO OVER HEAT.IF BLEEDING AIR OUT THE COOLANT SYSTEM DONT HELP AND COOLANT FANS DONT TURN ON YOU HAVE PCM PROBLEMS.

What you are describing sounds like there is air in the cooling system-Start the engine when it is cold with the cap off of the overflow and turn the heater up to full blast-make sure there is coolant in the reservoir, and keep an eye on the gauge, At the point where the thermostat opens, the level in the overflow should drop-top off the overflow filling to the 'full hot' mark on the side of the tank. Put the cap back on and drive it, watching the gauge. If you still have issues, you may have a problem with a malfunctioning thermostat. If it is alright after doing this, make it a point to check the level when it is cold again later to be sure the coolant tank is up to the 'fill cold' line.

to weaker mixture will cause vehicle to overheat ,but i think that the radiator cap rubber has perished causing the coolant to throw out or the head gasket ,get the cooling system pressure tested ,and then run engine with gauge attached to check for excessive pressure build up ,(head gasket test) ,another trick is to fit a bottle to end of the overflow pipe so what goes out gets sucked back in when engine cools .Check the rubber seal in teh rad cap and check the seating that it pushes and closes onto.As for the sliding doors use your judgement and you will not go far wrong

It sounds to me like you're low on coolant. When you checked the coolant level, did you actually open the radiator cap and make sure the radiator is full? The plastic tank you generally add coolant too is actually an 'overflow' or 'reserve' tank. There is a hose that runs from that tank to the top of the radiator so if the radiator gets low on coolant, more coolant -should- run in from the overflow tank. However in practice this does not always work. I have a Jeep that leaks coolant and experiences this exact same problem. Coolant will not run from the reserve tank into the radiator because the hose is plugged up, and whenever the radiator gets low on coolant the temp gauge will go real high and then drop, and the heater doesn't work well. This is because the cooling system of your car is supposed to be a closed system, full of coolant and no air. When coolant leaks out, the space it used to occupy is now occupied by air, which does not transfer heat well. When 'air' is passing through your cooling system, no heat can be transferred from your engine to the heater and radiator, resulting in a hot engine and no heat at the heater. Then when a pocket of water passes through the system, the temperature gauge quickly falls as the water absorbs the heat from the engine. The hot water that cools the engine is where the heater gets it's heat from as well, so when water passes through the heater core, the heater works, but when it's filled with air, it doesn't.

this was caused by the cap being gone, there is zero doubt of this, I hope u have not damaged the cylinder head gaskets, time will tell.