[hutch58]

My 98 V6 has a problem running hot. The car is driven daily by my wife who has a 40 mile (1 way) to work. She told me one morning that it took forever for the heat to start working each morning. I figured it was the thermostat and planned to replace it that w/e. However, before the w/e came the Stang ran hot on her...or at least that is what the temp gauge indicated. She was able to limp it home; stopping to let it cool and parked it. I checked the radiator and there was plenty of water so I started the car and watched the temp. After 15-20 minutes they temp gauge hadn't budged so I opted to give it a drive. After about 10 minutes of driving, the temp shot up and I pulled over. Playing around with the heater during this time, it did not seem to affect the temp until I turned on the heater which went from hot then cool; back and forth. Once the it cooled down, I drove home and replaced the thermostat and retested. Basically the same result. There is no indication the water pump is an issue so I'm leaning toward the heater core.

Is there a way to test the heater core? Any other suggestions? The Stang has roughly 200k miles (two speedo replacements) and has been a very good car. However, with 200k, things are starting to wear out. Front end appears to need some major repair; struts and ball joints (upper/lower) need to be replaced.

How expensive and difficult is it to replace a heater core? Can anyone either provide or point me to step-by-step (idiot proof) instructions to test and replace heater core if needed?

Thanks and Merry CHRISTmas!!!

[ESG-642T]

air in cooling system...

or head gaskets, if it overheated 8.5/10 head gaskets.

[6ER THEN I 8ER!]

Changing Heater Core on 96-98 Mustang

[stephen]

I can't imagine the heater core would cause overheating.

The heater not working correctly is usually due to low coolant levels. Since the heater circuit is at the highest part of the cooling system it will not work if the coolant is below
the top of the radiator. You will need to figure out where the coolant is leaking. A coolant system pressure tester will help with that. The first thing to do would be to remove the bleeder plug on the metal line coming out of the water pump and fill the system from there as well as at the radiator cap. That might fix the problem. If it fixes it temporarily then you should look for an external leak and fix that. If there are no external leaks but it keeps losing coolant there may be a head gasket problem.