Heating System woes

[IronTooth]

2000 Explorer XLT, 212k odometer, 4.0 OHV engine, 4WD

Symptoms:

1) Loss of heating efficiency from heating system - over a couple of months - to the point where there is virtually no heat coming into the vehicle at all, even at maximum temperature setting. #Until recently, I was thinking that it was my imagination, coupled with colder weather, but about two weeks ago, over a period of a couple of days, lost heat entirely.

2) Loss of coolant.


Additional Information:

A. When climate control (heat/air/defrost) is set to heater, and regardless of the temperature setting:

#- Coolant loss is accelerated, about 1 quart a week (figure 250-300 miles per week);

#- Engine temperature gauge will run slightly lower than normal, and shortly after acceleration, it will deflect slowly a couple of times about half way down toward the 'C' mark and back up again;

#- when stopping at a traffic light after sustained speeds over 40mph, and immediately after turning the engine OFF, there will often be a fairly loud, but diminishing bumping or thumping noise from the front of the vehicle (BUMP, Bump, bump...) at about 1.5 second intervals;

#- Coolant does not drain back to the radiator from the overflow tank.

B. When the climate control switch is set to 'OFF':

#- Coolant loss stops or is minimal, and coolant is drawn back into the radiator from the overflow tank;

#- #The engine temperature gauge, after initial warm-up, is steady at the 'normal' level for #this vehicle (centered on the icon), regardless of engine load;

#- I will sometimes hear a burble sound after the engine is turned off, which I am interpreting as the sound of coolant being drawn back into the radiator.

I see no obvious leaks in the engine compartment, especially not around the heater hoses or connections. #

There is no obvious (to me) odor of engine coolant when the heater is on, and no obvious unusual wet spots on the rugs. #I have not tried to look under the rugs for stains, though, so can't rule out a heater core leak.

Oddly, just about the time that I lost all heat, the engine threw a P0171 code.

Thanks for any thoughts for a cause or recommendations for further troubleshooting...

 

[mp223]

1) Loss of heating efficiency from heating system - over a couple of months - to the point where there is virtually no heat coming into the vehicle at all, even at maximum temperature setting. #Until recently, I was thinking that it was my imagination, coupled with colder weather, but about two weeks ago, over a period of a couple of days, lost heat entirely.

Your heater core may be plugged, heat your car up, turn the heater on full blast for a few minutes, then feel the inlet and outlet tube of the heater core, if the inlet and outlet is hot, things should be working as normal, and your issue may be the blend door. If the inlet is hot and the outlet is cold, your heater core is probably plugged. If your inlet and outlet are both cold, you problem is upstream. Check your heater control valve, it controls the amount of coolant flowing through your heater core.

2) Loss of coolant.

Check your heater control valve for leaks and cracks, check your hoses and check the bottom of the radiator for leaks. There is a black plastic cover that tends to pool with coolant when there is a leak from the radiator.

Since coolant loss is accelerated when using the heat, my first guess would be to replace the heater control valve (~$20) and inspect the hoses attached to it.

#- Engine temperature gauge will run slightly lower than normal, and shortly after acceleration, it will deflect slowly a couple of times about half way down toward the 'C' mark and back up again;

Change your thermostat. You also may have air in your system and need to burp it. Air could also explain why you have no heat- the heater core has air in it.