I'll be factual and fast:

1. 2005 Tribute, 13,000 miles (yes, 13k), pristine condition all around.
2. Bought from an elderly gentleman whom let the coolant reservoir run dry.
3. Zero heat.
4. Engine heats up normally, no over/under heating issues.
5. Pulled off return hose from heater core and nothing but air.
6. Forward and back flushed core, installed new thermostat, refilled system.
7. I then had heat, not great, but it was better than warm. I figured maybe there was a little air in the system that would work itself out.

All of that was last spring; it's now winter and 10 degrees outside.
1. No under/over heating issues; engine warms and temp needle doesn't budge from normal. Reservoir has proper fluid.
2. At idle, I get lukewarm air. Driving, I get very warm air. On the highway, I get hot air.

Ok, I know, you're going to say "WATER PUMP"...but this is what I don't get..

1. It's 10 degrees outside.
2. Car is operating temp.
3. Heat is on low fan setting (recycle inside air) blowing lukewarm air.
4. I grab the heater core input hose, right where it enters the cabin, and I can just barely keep hold because it's HOT!
5. I grab the exit hose and it feels like the same temp as the air coming out the vents.

Where is the heat going? This is just nuts...

If the water pump wasn't pushing water, or slow to push, why is the core input hose, right where it enters the core, so HOT? There's a good 5 feet of hose between the engine and where the hose enters the core; there's got to be a decent amount of water flowing to keep that hose hot the whole length in 10 degree weather.

The wifes' car has a flamethrower for a heater; even at idle in 10 degree weather it will cook you. I grabbed the core hoses in her car and the input was no hotter than mine but the out was much hotter even though it's dumping tons of heat into the cabin.

Someone Save Me

 

Get under the dash & locate the temperature flap actuator, watch to see its movement while some turns the heater dial from hot to cold & back. It may not be moving its full travel.

 

Thanks for the advice and I will check.

I have some additional info; I used a "no Touch" laser pointer thermometer to take some temps.

1. Came home from driving the car, so it was at operating temp and had decent heat while driving.
2. Parked the car and let it idle with fan on low recycle.
3. Outside air temp is about 20 degrees.
4. Hose surface temp where it goes into the core is 168 degrees.
5. Hose surface temp where it comes out of the core is 71 degrees.
6. Air coming out of the cabin vent is 62 degrees.

So, I'm losing 97 degrees between the input and output of the core, yet the air temp blowing out the dash is only 62 degrees.

The temp in the cabin is in the 40's, so I'm seeing a ~20 increase in air temp across the core...where is the other ~70 degrees of heat going?

At 5' from the engine the input hose, on the outside, is 168 in 20 degree weather, then the water inside the hose has got to be 200 or so; wouldn't you think.

I have hot water going in, 97 degree cooler water coming out, yet the vents blow cold air at idle...nuts.

 

Sounds like you have a partially blocked heater core to me.

The laws of thermodynamics don't mean you can add and subtract temps in that way but it does sound like not enough energy is coming out in the air from the heater, that means not enough is going into the heater core in the water. In simple terms energy is temp x flow so if temp is good (your high input water temp), then flow must be low.

Try a back flush of the core but I think you will have to replace it, the very low mileage has probably allowed sludge to form and settle in the core, then age has turned it solid.

 

I forward and back flushed the core; at low pressure, the water poured right through it and not a single bit of any dirt/sludge in the bucket.

My mind is cloudy with frustration; just hoping someone has dealt with this problem and would give a "for sure" answer.

I spoke with a Mazda mechanic today and he said that even when all is 100% correct, these 05 Tributes heat poorly at idle. The idle is sub 1000rpm by design as a slow running engine uses less fuel at idle...and it also produces less waste heat...which is what heats the cabin...so no/poor heat at idle makes sense.

Looking at, and thinking through, the plumbing today, the hose comes out of core to a T. A small hose off the T runs to the throttle bottle (to heat it up) and them comes back out of the throttle body and into another T. Both T's have a much smaller flow through hole than the hose that comes out of the core to force water through the throttle body.

I wonder if between the throttle body and the 2 T's it's obstructed? That would cut the flow into and out of the core. I may just disconnect the throttle body bypass to eliminate the T's and put a straight hose in to see what happens.

 

I wasn't aware of the TB loop but for sure you have poor flow through the core.

 

Without knowing the actual flow rate of the heater system, those temps don't tell us everything.

If there is normal flow rate and you're dropping that much heat from inlet to outlet, then the heat from the core is being lost somewhere (unlikely).

If you're showing that much drop in temp at the outlet with little cabin heat, you don't have enough flow through the core. Either the core is plugged and the water is trickling through, or it's still air bound from the earlier drain flush. A weak water pump impeller is another possibility.

There's probably a youtube video that shows proper procedure for burping the Tribute (check Escape as well).

John