sensor question

im one of many on this forum thats had trouble with the heater on the taurus. is there any possibility that some sensor could control the heater temp in any way? the reason im asking is, dispite all my backflushings and various attempts to restore my heat, its never worked. when its 70 outside, the heat works! when its cold, it dont! and my car surges a little if i dont let it warm up much on a really cold morning. just thinking maybe some connection. maybe im retarted

What year, what engine & how many miles? What have you done to correct the problem thus far? Change thermostat? Did you back flush the heater core and is there sufficent flow? Are the doors in the air passages opening and closing properly? After you've done everything else last resort is new water pump because the blades have a way of wearing way down.

Surges - Sounds like the MAF, mass flow air sensor, might need cleaning and dump in a can of Sea Foam available at auto parts stores. http://www.seafoamsales.com/motorTuneUp.htm

its a 98 taurus lx 140k mi. 6cyl auto. ive done a half dozen backflushes, 3 thermostats,both coolant sensors, waterpump, 4 radiator flushes, even had my head gaskets replaced during this time. blend door has full travel and all controls on the dash a in good working order. car never overheats.

I got'cha fine fordfool. Well, it sounds as if you've covered all the bases and surprisingly enough this is not the first time we have see your delima where you're about ready to throw up your hands and run screaming down the street. But don't abandon ship just yet because we have seen where they never ran hot but no heat and it ended up being the water pump blades worn down to nubs. Looking at them you'd think they were hardly capable of pumping any water a'tall, but apparently they pump enough to keep the engine cool, but not enough flow to push it through the heater core.

I wish I could tell you there was some way to test the water pump flow but with the age and miles on your Taurus about the only way to tell is pull the pump off and look at the blades. Take it to an auto parts store and ask to see a new/rebuilt pump and compare your blades to the new pump then you'll know for sure. I don't know about the 94's, but take the water hose off the pump and see if you can stick your fringer far enough in to feel the blades and compare them to a new pump and that way you don't have to take it off.

Only other thing I can come up with is if there's an air bubble in the heater core or you have the hoses to the heater core hooked up backwards.

ive replaced the waterpump already. the fins were worn amost all the way down, but now its new. the heatercore connections are factory.

'Fraid I ran out of ideas and unless there is a big bubble in the core I'm stumped. Park it on the steepest hill you can find front end high and race the engine a few times and if it is air bound that should blow the bubble to the highest point out the reservoir tank.

The IN hose should go to the bottom of the core fitting and the OUT hose to the top. If you have them reversed the core never fills up with coolant so never gets hot. When it fills from the bottom it pushes out the air through the top and thus the core fills with hot water and you should have heat. Are both of the heater core hoses hot?

Have a luncheon to attend so must run for now and I'll continue to think on it.

both hoses are hot. thanks for your input. if you have any other ideas, they would be greatly appriciated.

If both hoses for the heater core are hot, you are getting flow through the heater core. It seems the next place to focus is on the blend door in the cabin. Do you notice any change in temperature from the vents when you change the temp setting dial from full hot to full cold?

-Rod

yes, there is a noticable change. i removed the cover on the blend door and the door has full range of travel when changed back and forth.

Oh, well that's your problem! You removed the cover so the air doesn't need to go through the heater core!

Just kidding, with the cover remove and the engine warmed up, was the heater core warm to the touch?

Does the airflow seem comparable between full cold and full hot (according to the temp dial setting)?

I'll pull up the HVAC diagrams in the service manual and see if something jumps out as a likely cause.

-Rod

Okay, according to the factory service manual there is a blend door air temp variable resistor that controls the amount that the blend door opens or closes depending on air temperature. However, you mention that with the cover removed, you can see the blend door move completely in both directions, so the blend door thermistor must not be the issue.

Also, it appears that all air in the ventilation system flows from the blower motor through the evaporator core. Then air is either diverted through or around the heater core. If the inlet and outlet of the heater core is getting hot, the blend door works fine, and the blower motor is moving good air, the issue almost has to be a blocked heater core. Is there maybe a napkin stuck to the blend door side of the heater core?

-Rod