P1258 code Coolant coming back up to the reservoir and out the overflow hose.

I suggest changing the cooling thermostat to make sure it's not getting stuck causing temporary overheating and flush the system and put fresh coolant in.
The guage will go hotter then go back to normal every time the thermostat opens to let cooled water into the engine block which is normal. Time for concern is when the guage goes hot and stays there along with bubbling sounds and coolant overflow onto the ground. Which you probably already know.

Good job of tying the heater to the antifreeze overflow.

This is a guess. Replace the radiator cap and the hose connecting the radiator to the coolant reservoir. Then fill the radiator, engine, and heater hoses completely with antifreeze solution.

When the engine heats up, the coolant expands. Excess coolant is directed to the reservoir. When the engine cools, coolant is supposed to be sucked back into the coolant system. If either the radiator cap or the overflow hose has a tiny leak, air will be sucked in instead of the antifreeze returning

Yes, it should. Heat expansion pushes coolant through the hose into the reservoir. When coolant cools, it will siphon back into the radiator until radiator is full.

check to make sure the coolant is running freely into and out of the radiator. you can do this by squeezing the inlet and outlet hoses when the engine is cold, so you dont burn your hand.
also while the engine is cold, open the reserve/overflow cap outside the radiator, usually next to the side wall. with the cap off, one by one squeeze each cooling system hose, and see if it backs or forces coolant into or out of the overflow reservoir. if coolant comes out of the top inlet hole when squeezing a hose, the thermostat is probably stuck closed, if the coolant in the reservoir bubbles from below, you probably have a clog in the engine ports where the coolant passes by the head to cool it off. if you have ever put only water in the radiator instead of the proper mixture of coolant to water. there could be some mineral or calcium deposits clogging things.

Check ur radiator cap! Mostly when the engines become hot, coolant goes thru the coolant reservoir and comes back to the radiator when it cools down. Damage radiator caplet the coolant goes thru the reservoir but can't siphon back the coolant to radiator , thus always overflows the reservoir and the radiator dries out from its coolant! Check also if there is LEAKS in the bypass hoses and CAP PLUGS! Hope that might help u out!

Looks like bypass hose or engine coolant plug just got leak! look at ur coolant reservoir, it might overflowing when ur engine heats up and its dripping towards the engine! Look and search all the hoses in the side of the engine and reservoir! If its the bypass hose, there will be a difficulty in removing and replacing it, but u could fix it! taah!

TO CHANGE RADIATOR FIRST YOU TURN OFF RADIO FIRST TO KEEP FROM LOSING RADIO CODE.DISCONNECT NEGATIVE BATTERY CABLE.RAISE FRONT OF VECHICLE SUPPORT ON JACK STANDS.REMOVE THE LOWER SPLASH SHIELDS.NOW YOU NEED TO DRAIN THE COOLING SYSTEM.CATCH COOLANT IN A LARGE DRAIN PAN.REUSE COOLANT IF ITS FAIRLY NEW.IF COOLANT VERY OLD CHANGE IT.PUT OLD COOLANT IN SOME EMPTY CONTAINER TAKE TO A GARAGE OR WHOEVER DISPOSE IT.DONT POUR ON GROUND.HARMFUL TO THE ENVIRONMENT.MOVE THE AIR INTAKE DUCT PASSES OVER THE TOP RADIATOR HOSE.NOW WHEN ALL COOLANT DRAIN OUT.LOOSEN UPPER AND LOWER RADIATOR HOSE CLAMPS.THEN DETACH THE RADIATOR HOSES FROM THE FITTINGS.IF THEY ARE STUCK GRASP EACH HOSE NEAR THE END WITH A PAIR OF ADJUSTABLE PLIERS AND TWIST IT TO BREAK THE SEAL THEN PULL IT OFF REMOVE SMALL COOLANT SURGE LINES FROM TOP OF RADIATOR THAT GOES TO THE OVER FLOW RESERVOIR..DISCONNECT COOLING FAN ELECTRICAL CONNECTOR.THEN REMOVE THE COOLING FAN.REMOVE DISCONNECT AUTOMATIC TRANSMISSION COOLER LINES GET READY TO CATCH TRANSMISSION FLUID THEN PLUG LINES. NOW UNSCREW THE FOUR BOLTS TWO ON EACH SIDE OF THE RADIATOR THAT ATTACH RADIATOR TO THE AIR CONDITIONER CONDENSOR CAREFULLY TIP TOP OF THE RADIATOR SLIGHTLY TOWARDS THE ENGINE.REMOVE THE UPPER RADIATOR SEAL AND LIFT RADIATOR FROM THE ENGINE.NOW IS THE TIME TO REPLACE THE UPPER AND LOWER RADIATOR HOSES WITH NEW ONES SINCE ALL COOLANT REMOVE I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.NOW WHEN YOU GET READY TO INSTALL NEW RADIATOR USE SHEETS OF CARD BOARD PROTECT RADIATOR FINS AND CORES FROM DAMAGE WHILE SITTING RADIATOR BACK IN PLACE.ONCE YOU GET UPPER AND LOWER HOSES IN PLACE ALSO PLACE SMALL SURGE HOSES FROM THE OVER FLOW RESERVOIR TO RADIATOR NEW THERMOSTAT AND TRANSMISSION COOLER LINES ALL HOOK UP. START POURING ANTIFREEZE IN THE RADIATOR OR OVERFLOW RESERVOIR IF RADIATOR DONT HAVE RADIATOR CAP ON IT.POUR A FULL GALLON ANTIFREEZE AND A HALF MORE IF LONG AS THE COOLANT STAYS ON THE COLD LEVEL MARK ON OVERFLOW RESERVOIR DONT OVER FILL.IF YOU POUR ANTIFREEZE IN RADIATOR KEEP POURING ANTIFREEZE UNTIL LEVEL STOP DROPPING AND LEVEL OFF AT RADIATOR TOP.START ENGINE CHECK FOR LEAKS. LET ENGINE RUN UNTIL IT WARM UP TOP RADIATOR HOSE GET HOT.WATCH COOLANT LEVEL IN RADIATOR OR COOLANT OVERFLOW RESERVOIR WHEN THERMOSTAT OPENS COOLANT LEVEL WILL DROP.ONCE YOU HAVE ENOUGH COOLANT IN THE SYSTEM COOLANT LEVEL WILL STOP DROPPING.THEN YOU READY TO GO.LET ENGINE SIT A LITTLE WHILE CHECK COOLANT LEVEL AGAIN.COOLANT LEVEL IN THE OVER FLOW RESERVOIR SHOULD BE AT HOT MARK FOR HOT ENGINE AND WHEN ENGINE COLD COOLANT LEVEL SHOULD BE AT THE COLD MARK.IF POUR ANTIFREEZE IN THE RADIATOR COOLANT LEVEL SHOULD BE AT TOP OF RADIATOR BELOW PRESSURE CAP.

Probably from the overflow hose reservoir next to the radiator. When a car is ran it heats up and the coolant expands into the reservoir and some may go out the overflow hose. When it cools down there will be coolant in the white plastic reservoir and the engine will **** that up back into the engine until it fills up and the process will start over again. Just make sure the reservoir has fluid in it.

you should have a coolant reservoir that the overflow hose runs to, the vehicle pulls coolant out of the reservoir as needed, as well as pushes it back in, could also be a stuck thermostat or a weak radiator cap, if you replace the cap make sure you replace it with one of the same pressure rating.

That will be your over float goes no where but down, there should be another hose that goes to the radiator.