97mitsubishi..3000gt overheating what would cause it to overheat,even though there's plenty of coolant in the overflow container/

If your 1998 Cutlass is overheating and the heater is blowing out cold air, and you are also noticing that coolant is leaking out, there are a few possible causes. Here are some things to check:

Check for a coolant leak: Start by checking the engine and radiator for any visible signs of a coolant leak. It's possible that a hose or other part of the cooling system may be damaged or loose, causing coolant to leak out.

Check the radiator: If the radiator is not working properly, it can cause the engine to overheat. Check to make sure the radiator is not clogged or damaged.

Check the water pump: The water pump circulates the coolant through the engine. If it's not working properly, coolant may not be flowing through the system correctly, causing the engine to overheat.

Check the cooling fan: The cooling fan helps to keep the engine cool by pulling air through the radiator. If it's not working properly, the engine may overheat.

Check the thermostat: Even though you recently replaced the thermostat, it's possible that it's not working correctly. A faulty thermostat can cause the engine to overheat.

It's important to address any issues with the cooling system as soon as possible, as overheating can cause serious damage to the engine. If you are not comfortable diagnosing and repairing the issue yourself, it's recommended to take your car to a qualified mechanic.

The high pressure in your cooling system could be caused by several factors including:

Overheating engine: If the engine is running hot, it will cause the coolant to expand and increase pressure in the system.
Malfunctioning radiator cap: A faulty radiator cap can cause pressure to build up in the system and force coolant out of the overflow container.
Blocked coolant passages: If the coolant passages are clogged with debris or rust, it can cause the coolant to get trapped and increase pressure in the system.
Air pockets in the system: Air pockets can develop in the system, causing pressure imbalances and coolant to be pushed out of the overflow container.
If you are experiencing high pressure in your cooling system, it is recommended to have a professional diagnose and fix the issue to prevent damage to your engine and cooling system components.

CAR OVERHEATING FIRST CHECK FOR LOW COOLANT IN THE RADIATOR COOLANT OVERFLOW JUG.IF COOLANT LEVEL IN OVERFLOW JUG LOW REFILL ADD COOLANT BACK TO THE FULL COLD MARK.PUT RADAITOR CAP ON COOLANT OVERFLOW JUG START ENGINE LET IT IDLE UNTIL IT OPERATING TEMPERATURE.MAKE SURE TOP RADIATOR HOSE GETTING HOT WHILE ENGINE WARM UP.IF TOP RADIATOR HOSE DONT GET HOT WHILE ENGINE IDLING YOUR THERMOSTAT COULD BE STUCK CLOSE CAUSING CAR TO OVERHEAT.IF TOP HOSE IS GETTING HOT.CHECK FOR COOLANT LEAKS CHECK TOP RADIATOR HOSE AND BOTTOM RADIATOR HOSE FOR LEAKS.CHECK FOR LEAKS AT THE RADIATOR CORES AND PLASTIC SIDE CONTAINERS.IF ALL IS GOOD ENGINE OVERHEATING WHILE IN A LONG TRAFFIC LINE, COOLANT FANS NOT COMING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR BLOWN COOLING FAN FUSE OR RELAY.COULD HAVE PCM FAULT.MAKE COOLING FAN ELECTRICAL CONNECTORS AND WIRING NOT DAMAGE OR BROKEN.

First you need to check and make sure that your water pump is working and circulating the coolant. If it is, then pull your oil dip stick and look closely for any sign of water/coolant on the dipstick. And then look for an oily film on the coolant. If you see either or both of these conditions, then you need to check for either a blown head gasket or a cracked block.

And no a heater core would not have that much effect on whether your car overheated.

Sounds like the head gasket is blown and pushing the coolant out of the radiator. Here is an article that will help you find out the real cause, though.
How to diagnose an overheating engine
Hope it helps!

Hello and welcome to FixYa! If you have overheating problem, it can lead to multipleissues. You may be running on low coolant that's why the vehicle overheats. Ifthat's the case, please add coolant and make sure that it sits on the rightlevel, too much coolant can cause overheating too for coolant will overflow. The vehicle may have a faulty or worn out radiator blowermotor that's why it overheats. If that's the case then you will need a blowermotor replacement to resolve the issue. If the radiator is clogged with dirt and rusts this issueoccurs too. The coolant doesn't flow normally on the cooling system if it'sclogged. If that's the case, I strongly suggest that you have the radiatorflushed to drain out dirt and rusts. If you think that the radiator served youenough then it's better to have it replaced. Please do check the radiator hoses, If you have worn outhoses it can cause coolant leakage which can result to overheating. A tiny holeis good enough for the vehicle to overheat. A faulty thermostat sensor can cause the issue too. If youhave worn out thermostat, the fan may not trigger that's why the fan won't workwhen under stressed conditions. A blown radiator blower fuse can cause thisissue too so I suggest that you check the radiator blower fuse and replace itwhen necessary. What causes the radiator blower fan fuse to blow? It's becauseof a failing radiator blower motor, If that's the case have the radiator blowerfan motor replaced. If the fluid in radiator doesn't circulate then it meansthat you have a blown head gasket or a faulty water pump. I suggest that you gofor the water pump replacement first specially if you think that it's near theend of it's service life. Usually, water pops out the radiator when engine isreved (a sign of faulty water pump and possible blown head gasket). Hope you find this information helpful enough and thank youfor using FixYa! Have a good one!

Whenever you overheat once, then the thermostat must also be replaced. It is operated by the expansion of a contained wax pellet, and overheating causes permanent loss of wax.
However, you may also have caused a head gasket leak now from heat warpage. If the thermostat does not help, then borrow a cooling system pressure checker from a place like Autozone, and see of it holds pressure for 5 minutes after pumping it slightly above cap rating. Then start engine and see if it is steady or oscillating from 1 cylinder leakage.

Oil in the coolant caused by blown head gasket or cracked head. This will also cause overheating. :o(

Have you changed the water pump ?

If the head gasket goes water is allowed to seep into the cylinders and then out of the exhaust.

Once the level has dropped enough the car overheats

Or the water is pressurised in the radiator from the compression of the engine and it is forced out of the overflow leading to coolant loss and overheating