Heater Core causing OVERheating?

If you unplug the connector on the temp sendin unit right beside the thermostat the fan will come on on high all the time(will at least it does on my car) I keep mine unplugged in the summer.

Zero_chance said:

On the fan connector, the black is the ground and the other two are low and high speed settings. You should be able to test the actual fan op that way. If its bad then you know what to replace. If it turns on hooked directly to power and ground, then the CCRM has gone south. It controls fan speeds as well as a few other PCM operations. Theres non serviceable relays inside of the CCRM, likely solid state though Ive never actually taken one part to confirm.

Click to expand...

make sure you don't put power to hi and low at the same time. fubar for sure

running hot

i have nothing on 5.0 . this is from 03 but should be enough to read on electric fans...SECTION 303-03A: Engine Cooling 2003 Mustang Workshop Manual
DESCRIPTION AND OPERATION Procedure revision date: 11/12/2002

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Engine Cooling Printable View (14 KB)
CAUTION: Vehicle cooling systems are filled with Motorcraft Premium Gold Engine Coolant VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Always fill the cooling system with the same coolant that is present in the system. Do not mix coolant types.

NOTE: The addition of Motorcraft Cooling System Stop Leak Pellets, VC-6, darkens Motorcraft Premium Gold Engine Coolant from yellow to golden tan.

The 4.6L cooling system components include the:

block heater
engine coolant temperature (ECT) sensor
fan blade, fan motor and fan shroud assembly
radiator
pressure relief cap
radiator draincock
coolant pump
coolant thermostat
oil filter adapter
radiator overflow hose
upper radiator hose
lower radiator hose
The radiator overflow hose circulates the coolant.

The coolant thermostat:

controls the engine coolant temperature.
allows for quicker engine warm-up.
The degas bottle/coolant expansion tank:

provides a location for service fill.
contains coolant expansion and system pressurization.
provides air separation during operation.
replenishes the engine coolant to the system.
The engine coolant flows:

from the lower radiator hose to the coolant pump.
from the coolant pump to the engine block and the cylinder heads.
The 3.8L cooling system components include the:

block heater
engine coolant temperature (ECT) sensor
fan blade, fan motor and fan shroud assembly
radiator
radiator cap
radiator draincock
coolant pump
coolant thermostat
oil filter adapter
radiator overflow hose
coolant expansion tank
upper radiator hose
lower radiator hose
The fan blade draws air through the radiator to help cool the engine coolant.

The fan motor:

operates only when the ignition switch is in the RUN position.
will not operate with the switch in the OFF position.
The engine coolant:

flows through the radiator tubes and is cooled by passing air over the cooling fins.
is then circulated from the radiator outlet tank through the coolant pump and into the cylinder block to complete the circuit.
A closed coolant thermostat returns the engine coolant to the coolant pump. An open coolant thermostat allows the engine coolant to flow to the radiator.

CAUTION: Engine coolant provides freeze protection, boil protection, cooling efficiency, and corrosion protection to the engine and cooling components. In order to obtain these protections, the engine coolant must be maintained at the correct concentration and fluid level in the degas bottle (4.6L) or coolant expansion tank (3.8L).

When adding engine coolant, use a 50/50 mixture of engine coolant and deionized water.

To maintain the integrity of the coolant and the cooling system:

NOTE: The addition of Motorcraft Cooling System Stop Leak Pellets, VC-6, darkens Motorcraft Premium Gold Engine Coolant from yellow to golden tan.

Add Motorcraft Premium Gold Engine Coolant VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Use the same coolant that is present in the cooling system. Do not mix coolant types.
Do not add/mix orange-colored Motorcraft Speciality Orange Engine Coolant VC-2 or equivalent meeting Ford specification WSS-M97B44-D. Mixing coolants may degrade the coolant's corrosion protection.
Do not add alcohol, methanol, or brine, or any engine coolants mixed with alcohol or methanol antifreeze. These can cause engine damage from overheating or freezing.
Do not mix with recycled coolant unless it meets the requirements of Ford specification WSS-M97B51-A1. Not all coolant recycling processes meet these Ford specifications. Use of such coolants can harm the engine and cooling system components.
The coolant temperature sensor (4.6L) or cylinder head temperature sensor (3.8L) provides a signal to the temperature gauge.

The optional block heater:

electrical heating element is installed in the core plug opening.
uses a standard 110V electrical supply
keeps the engine coolant warm during cold weather.


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Fan Control
The PCM monitors certain parameters (such as engine coolant temperature, vehicle speed, A/C on/off status, A/C pressure, etc) to determine engine cooling fan needs.

For Variable Speed Electric Fan(s):

The PCM controls the fan speed and operation using a duty cycle output on the Fan Control - Variable (FCV) circuit. The fan controller (located at or integral to the engine cooling fan assembly) receives the FCV command and operates the cooling fan at the speed requested (by varying the power applied to the fan motor).

Same general idea with the newer stlye setup but controlled a little differently. As for unplugging the temp sensor, that still relies on the PCM seeing that input and then directing the CCRM to turn the fan on. The only definite way to check the fan would be to get a jumper wire, hook a ground to the black wire of the connector on the fan side, not the harness side, and then get a single power wire and touch it to either of the other two wires (but not both simulataneously like pointed out). If it comes on, fans good.

dont take this litely

my 03 cobra cracked a head over this problem.. i dont know the style of your fan but on mine all of the fan blades are connected by a plastic ring...the ring cracked and when fan starts to spin the fan blade gets jambed and fan wasnt spinning even though the fan worked

heat

thats great....as to smell..maybe give it a week of burning hot ,,and check to see if the door (outside air)is closing?

the smell

yea if your heatercore has not been getting hot for awile thier could be a buildup of who knows on it,,,,i do believe it should always be as hot as the radiator..which if you spill antifrezze on it it has to burn off? just a thought

maximos said:

What are the major signs of a bad heater core? I've suspected for quite some time that mine is going south because it started to smell like exhaust whenever I turned on the heat. Lately it's been exceptionally cold in Columbus, OH and my car has been running very hot almost to the point of overheating. The only way I can get the temperature to go back down is to turn the heat on and off until warm air comes out and takes heat out of the engine bay. Has anybody else experienced anything similar to what I've said?

It's important to mention that I installed a Mishimoto radiator and a new OEM fan about three months ago. I can't imagine that the radiator or the fan has gone bad already. I have a small coolant leak on the driver's side in the front as well. I suspect that it's just a cracked hose though. I haven't been able to investigate it due to weather.

If anyone has experienced this or knows a solution, please let me know.

Click to expand...

My heater core just went on me. You will experience fluid leaking from the lower firewall on the passenger side. There is an A/C condensation weep hole which doubles as an exit for coolant when the core ruptures. If you are losing coolant or smelling coolant it needs to be addressed. You can bypass the core for now, but if that is not the problem I would definitely replace the thermostat and the radiator cap because you could be overheating from a closed or partially closed thermostat and overheating will damage the seal on your radiator cap. Both are cheap and easy to replace. Attached photo is how i bypassed my core. Easy fix with a heater hose connector 3/4" to 5/8" and you use the 2 hose clamps present or buy 2 new ones. good luck!!

i noticed after i was halfway done typing .....figured to post it because itll

hmm good idea just connecting those hoses together and bypassing. I might do that the coolant smell is horrible.