Ok fellow Car Techs...

[Sweeper]

1992 Ford Mustang 2.3L

Problem: Temp guage reading very low and warm air out vents (not hot)

Customer complaint: Heater not working properly.

Parts replaced:

1) Thermostat
2) Flush, clean, fill radiator x2
3) Replace radiator
4) Replace thermostat
5) Flush Heater core (seperate) from engine to check for proper flow. No restriction noted.

RESULT: Still, warm air from vents, (vent door functioning properly), and engine gauge temp very low. Car will not get to proper temp area. The gauge just shows N O R M A L top to bottom. The N being the top of the gauge and the L being the bottom. The needle never rises above the A. Mixture of Anitfreeze is correct. Vent door functions perfectly. Heater knob works also. Car never reaches proper temp to open Thermostat to allow for flow. First time I have run into a situation where an engine will run cool enought to keep the Thermostat closed or let it open just barely.

Help if you can.

[Cruez]

There are quite a few new cars that need to be topped off other than filling the radiator...

There very well could be a air pocket inside the block or intake (depends on the car).

Check also to make sure your fan (if electric) is not running all the time... makes it take a lot longer to warm up.... (or the clutch fan, if its mechanical)

[RedFury]

Best way to determine what is going on....

Grab ahold of the radiator hoses and see what the temp difference is. The upper radiator hose should be hot enough that you can only hold onto it for a few seconds. The heater core hoses should be similar...you should only be able to hold onto one of them for a short period. If they are both cool enough that you can hold onto them barehanded and not get uncomfortable, then you've got a serious problem going on. The only thing that I know of that can keep and engine running cool, other than the lack of a thermostat, is an overly rich condition, as the excess fuel will cool the cylinders.

It is possible that you may have a partially plugged heater core, depending on how the core is mounted ( above , below, or parallel to the input/output lines ). If the core "hangs" by the pipes, then you could have sediment buildup, and the antifreeze is just running across the top and out the other sided.

[Sweet]

tha 92 mustang has a thermostat dat can be put in backwards unless u pay attention to tha arrows on the top and bottom..... Unless the thermostat is positioned correctly, the heater will never engage, as ther is a sensor that runs to tha unboard computer that controls the thermal and electrical actions... connect the lower computer harness to a diagnostic machine such is found in a machine shop, and test for the output of the float vaulve, the float throat, and the control feature in the onboard compl. under the seat... do not disclude the throatle cont. switch on the injection controller on the inboard fuel control valve, located under the hood........

[Ed_S]

Similar (if not identical) situation on my son's '93 Mustang convertible - 2.3L auto. Car simply won't warm up properly in cold weather. In our case, I'm sure it's related to an A/C problem - the compressor clutch is shot & the belt's gone. Since that belt drives only the compressor, Jeff's chosen to leave it go - he's pretty independent about the car & won't let me pay for his parts. Says "who needs air in a convertible anyway?" I'm kinda proud of his independence, so why force the issue? But - since the compressor also runs when the defrost is on he's got no defroster!!
Besides that, the car generally runs cold - guage never goes up much, never did, even in summer. Can't find anything wrong other than the above.

[sweeper2]

this is probably dumb, and you probably already have done it, but have you unhooked the fan to see if the car overheats or gets hotter....and as said above, make sure the hoses are putting out or receiving enough flow. Also make sure it's not normal for this car to run this way, might be normal operating temp. also have you ran the inside blower on low and then high and compare temps with a readout?...just some thoughts.....good luck

and....May The Force Be With You

Worst case scenario . . . blown head gasket.

Have you had the system pressure tested? We had a Taurus that had a cracked coolant resevoir, only ~$30 to fix it.

[Sweeper]

Car was pressure tested and tested "OK".... it was left on overnight and the next day it had dropped. Checked for leaks in heater core and engine, none were found. Coolant in resevoir still full. We have gone over this car and come up with nothing. The difference between the temps going in to the heater core and coming out are about 15 degrees difference with the fan on "HIGH" inside. Which Mitchell OnDemand deems normal. Upper and lower hoses are about the same. Fan is electric and comes on at 190 degrees which means it "rarely" comes on, but, verified that it works. Cars runs excellent also. No misfires, no rich/lean conditions. Just not enough heat. Coming from the vents at 55MPH the temps read around 130F. My Ford Ranger reads close to 200F and we tested a 96 Chevy S-10 and it ran 160/150F from the vents. So the max temp out of the vents is 130F and at 55MPH the engine gauge shows a temp near the bottom.

[whitebeard21]

I suspect a plugged heater core. A heater core can become plugged both internally and externally. Also vacuum controlled water flow valves can become stuck.
Take both hoses loose at the block and hook a garden hose up to the discharge side (largest hose) just hold the two hoses together as you dont want to put a full 40-60 psi on the heater core. Tie the other hose to something so it is pointing away from you because when it blows the gook out it will whip around and drown you in crud. External blockages (low air flow or funny noise) can only be fixed by removing the blower and vacuuming the leaves out and ocasionally you have to remove the heater or ac core ( depending on which is downstream first in the airflow) and Vacuum/blow the ground up leaves out of the fins.
this is a generic fix I have used on various makes of cars and trucks. I just had to remove my ac core and clean the leaves out to get my air flow back to normal. I am now looking for a nice piece of 1/8 stainless steel screen to fasten over the outside air intake on on all of my vehicles. I have an oak tree in the front yard that can cover the intake and windshield in only a day.

[nunyadam]

what temp is the thermostat opening at?
you can always throw it in a pan and cook it to see.
if everything else checks out put a hotter thermostat in.