No heat- just blowing cool air

[vannaksao]

I've looked for threads that might help, but I either can't find one that answers all of my questions, or the issue is half accurate. I'm going to try and make this as short and detailed as possible.

I was driving to work the other day (going up I-95 on Monday at 7am), kind of sitting in traffic- approx 30-40mph, stop and go. Woohooo! All of the sudden, I kind of feel my car bog, and it feels like I lose oil pressure. I step on the pedal, but the car barely moves, and it barely revs. I look down at my temp gauge and the tach is past the bar and hovering above the H! So in a panic, I turn up the blower (dial shows 4 fans), and max the temp to 90 degrees. It helps out a little- I see the temp start to drop a little. Also, luckily, the traffic starts to disappear and we start to move again. Now I'm going about 80mph with the fan and temp as high as they can go, and tach comes back down a little lower than halfway, where it should be. THEN, while I'm still driving, the hot air thats blowing turns into cool air. The temp is at 90, but the air is super cool. I get to work, shut off the car, and go inside.

I got home- changed the oil and filter, flushed and added new coolant. No radiator leaks. Seems like the water pump is working- I had the radiator cap open, with the car running, and it seemed like coolant was moving. But maybe its going bad?

1. The car only starts to overheat when its NOT moving. When it just sits in park/stopped, eventually the tach starts to climb. When the car is moving, the tach stays in the middle, but SOMETIMES it was climb just a LITTLE, about halfway- maybe a pinch above that.

2. The blower is working, but 90 degrees is more like 65-70.

3. SEL is on because of P0507. I'll have to perform the Idle Air relearning.

I'm thinking maybe I have a T-stat thats on its way out? Bad cooling fan? Waterpump? Heater Core? Any advice would be great.

Thanks ,
Vannak

[ARKQX33V6]

Coolant temp sensor will modify idle so will A/C will idle faster, but hi heat when not moving may be a plugged or partial plugged radiator. The coolant pump will move or cycle coolant around the circuit but if it is worn, shot or not in good shape the volume of coolant it moves will be low and cause hi heat. The T stat may be out as to its working shape and does not respond until excessive heat.

You must verify the stat, the pump and the radiator. The stat and pump will require work but a simple way of testing the rad: use of an infra red temp sensor, barring that a hand gingerly feeling the rad top, bottom and middle.

With the rad having a different temperature big enough for you to feel may be a plugged rad. A difference of 15 F at a 200 F range may be difficult to sense, but an infra red scanner can do it very easily.

Running you fans and with the heater on will cool the system a bit but the interior rad is small compared to the cooling rad.

You need to also verify the refrigerant A/C and make sure the A/C delivers cold air with the mixer chamber in A/C with no heat from the cooling system

[vannaksao]

I was able to decipher about 40% of what you were saying.

"Coolant temp sensor will modify idle so will A/C will idle faster,". Are you just implying that my idle will adjust according to what the coolant temp sensor tells it to do- just like running my a/c? I'm aware of this, and understand what you're saying, but I don't think this has any direct correlation to what my issue is.

"hi heat" - You meant "Overheating" right?
"plugged" - You meant "clogged" right?

The radiator is good. I just bought it last year, and just tested it for cloggs and leaks.

"Running you fans and with the heater on will cool the system a bit but the interior rad is small compared to the cooling rad." - I'm not sure what you're trying to get at. My a/c works fine, it's just the heat that is not working properly.

I just went out to my car, on my break, and I started the car. It ran from 12:15 -12:45, and did NOT overheat. The temp gauge didnt even go up to half. I guess this is a good thing. Maybe it's the t-stat that is starting to fail. But still, NO heat. Put it on 90 again and the air was as cool as the Pink Panther.

[ARKQX33V6]

Inside the car is a rad that is used to heat the interior. a no heat condition when you call for heat can be:
the conduits are blocked going to and/or from this inside rad or heat exchanger.
The directional valve is broken or its actuator is broken.
The 90 degree setting of the heater control may be broken or mal-adjusted
The digital control has lost its Digital to analog conversion within the controller.

Yes it is good that the car could run idling and not overheat, but the heat indicator, temp indicator should be at the normal range in about 10 minutes of start up

Your main rad in front of the car is your main heat exchanger to control the amount of heat in the form of BTU required to cool the engine, the rad gets about 230 F and is cooled with ambient air. This coolant then flows to the rad inside the cabin of the car, where it has a modulating valve to use more or less coolant that is at operating temperature to heat or provide cooler non A/C air for your comfort. A/C air from the A/C rad condenser and inside the car rad, evaporator allows cold A/C air to mixand mingle with the controlled amount of hot air.

With the A/C on and the heater on hot and cold air can mix to produce dry air for windshield demisting. The A/C gets easily overwhelmed by the heater and will produce a greater hot air than cold when mixing because there is a greater amount of BTU in the heated air than in the colder A/C air.

But if I understand your problem is not enough heat. If that still is the case:
Verify the main rad is at operating temp
Verify the internal rad for comfort air is not blocked and that coolant does flow to it and from it.
Verify the comfort level controller on the dash is working, also that the A/C is truly shut off with the controls off. Try the heater control at different temperatures from low to high in gentle steps, this controller may be stuck at a fixed no heat temperature from the passed Summer.

DO NOT FORCE ANY CONTROLS but do set them and take a thermometer and place in the ducts to see if you get any temperature change as you change the settings and be slow about the changes as the truck senses what you are asking in the settings and provides the digital to analog conversion to cause the analog controller to do what you want.

You may find that everything is as it should be but the heat if off from a summer time lack of use in heating.

Your other concerns are answered by your present no over heat condition.

[vannaksao]

Just checked the FSM. Per page HA-144, T-stat could be an issue. That would also explain the overheating. I'm gonna swap it out, and see what happens. Thank you ARK, I'll keep everyone posted.

[ARKQX33V6]

With the stat out stick it in water with a thermometer and start heating the whole thing up on the stove and watch the thermo opening for open movement. Record the temp it starts moving. This will help you decide if its good or bad.

If the motor is at temperature and you're not getting heat look to
heat controller
Electrical control devices
Blocked heater core for interior heating
Blocked passage ways to and from heater core

[vannaksao]

Just changed the t-stat. (drive belts too, just because I was already down there)

Took it for a couple of test runs. No more overheating! The real test will be the drive, in traffic, to and from work this week coming up. Still no heat though. Gonna check the heater core and controller, etc...

[ARKQX33V6]

Do the obvious checks first
Knowing how things work will help in diagnosing
When all things that are obvious fail, check into the details
as an example: coolant flow to the interior heat exchanger can be obstructed by:
crushed main coolant lines, plugged radiator (inside the cabin) these would be the obvious. But the not so obvious are the controller and the output valve being controlled. So you need to look at the details. Does the control work if so does it control the out put which in turn controls the input to the actuator. Now does the actuator work.

In simpler times we used a cable that we pulled or pushed to get more or less heat from the interior heat exchanger. But now with solid state and digital controls the control may be on/off or digital but that control operates a valve that opens more or less as the output from the control gives a greater reading to the input of the valve itself. Digital along with analog.

The digital controller can also be at fault...power supply, useful on power to off power, bus connections etc.

The more complex a controller the easier it seems to us to be able to do the job, until it fails

[vannaksao]

When I got home from work today, I tightened the new belts. They were squeeking a little, so I adjusted them according to specs in the FSM.

After all that engine starting and stopping, I decided to try the heat again. This time.....

we got HEAT!!! Maybe during my last attempt I didnt give the engine enought time to heat up? Maybe taking the Air Relief Plug of the Heater Pipe did the trick. When I did, a bunch of air, and some liquid (like someone squeezing a water bottle with only a few drop of water left in it) came out.

Anyway, problem solved. The VC/V Bypass/V is next on the list, along with a new fuel filter.

Thanks ARK.

Vannak