Heater in car is crapping out.

[Cheeseybacon]

Question for you automotively inclined folks. I've noticed over the past few days that the output from the heater in my car is beginning to slip. It was especially bad this morning and I haven't had to time to look at it yet, but I figured I'd ask here first to get an idea what to investigate first.

The only time my car's heater really produces heat in any kind of "normal" quantity is when I'm really working the engine hard in the upper RPMs, the moment I upshift into high gear and start cruising at a lower RPM the heat production ceases almost immediately. It also takes much much longer than before to get any heat at all out of the thing, even after the engine has very much been warmed up for quite some time.

Anyone have any idea what is the likely culprit?

[RUDY850]

could be the thermostat is sticking. Not opening up the whole way

[bogey1]

could be the thermostat is sticking. Not opening up the whole way

before you get a thermostat, try tapping on the housing with a hammer, lightly. sometimes that makes them open up..

[medicjz]

A few questions that may help find the problem...

1. What type of Vehicle?
2. Have you noted any type of "film" on the inside of the windshield when you turn the heat on?
3. Have you noticed that air does not blow out of where the selector is marked that it should be blowing out?
4. When was the last time you had the collent system flushed and possible had thermometers(sp?) changed?

What you may need to do is take a piece of cardboard and block a small area of you radiator, this decreases surface area to cool the antifreeze, which in turn makes the heat work better. Use caution with this however due to it can lead to over heating when at idle or when seasons change and you fail to remove the cardboard.

[BradC]

A few questions that may help find the problem...

1. What type of Vehicle?
2. Have you noted any type of "film" on the inside of the windshield when you turn the heat on?
3. Have you noticed that air does not blow out of where the selector is marked that it should be blowing out?
4. When was the last time you had the collent system flushed and possible had thermometers(sp?) changed?

What you may need to do is take a piece of cardboard and block a small area of you radiator, this decreases surface area to cool the antifreeze, which in turn makes the heat work better. Use caution with this however due to it can lead to over heating when at idle or when seasons change and you fail to remove the cardboard.

Agreed...more info. Make/model, etc, etc...

[Cheeseybacon]

A few questions that may help find the problem...

1. What type of Vehicle?

It's a 1995 Honda Civic. It has just over 200,000 miles on it now. It's beginning to burn some oil but otherwise runs it really well. It sure would be nice to get another 100,000 out of it.

2. Have you noted any type of "film" on the inside of the windshield when you turn the heat on?

Haha, film on the windshield? You should see how filthy, smeary and nasty my windshield is! I haven't cleaned it in many months, posssibly years, so yes, there's film, but it could be from anything.

3. Have you noticed that air does not blow out of where the selector is marked that it should be blowing out?

Nope, airflow is not a problem and always seems to come out of the vents that are selected. My problem is the air that is coming out suddenly goes from hot to cold.

4. When was the last time you had the collent system flushed and possible had thermometers(sp?) changed?

The headgasket blew at 136,000 miles. I took that opportunity to replace the thermostat and the water pump while I was in there. Obviously fresh coolant was put in at the time with the new headgasket, but it hasn't been changed since then. Think my coolant is to blame?

[BradC]

When the headgasket shit out, was the cooling system flushed? There could be an oil film on the inside of the heater core diminishing heat-transfer, but that wouldn't be an intermitten issue...

I would check the t-stat...

Heater switch could be f'ed too...

Does it ever smell like coolant?

[Michele]

Thermostat, heater core?

[Zef_66]

Regardless of make, model, years, miles, etc.

If the vehicle is over 5 years old or over 100k miles, then I would suggest that you change the t-stat and do a coolant flush and refill with new coolant. You coolant can get deposits in it over time, and these can build up in your heater core. This will reduce the amount of heat transfered through the heater core. And a t-stat can wear out over time and get weak.

Also, have your charging system checked. If your charging system is not up to par, your blower motor may not be running at full potential, thus not as much heat coming out.

Again, just some general guidelines. But make, model, etc does help.

Edit: Sorry it took too long for me to read and post my response. Take it FWIW.

[Hawk]

This is an easy one to diagnose.

Most likely cause of suddenly hot then cold and hot at high RPM's cold at low rpm's:

1- Check fluid level - take off the cap and see where the level is, if low add antifreeze, if it looks like a normal level, run the car until the therm opens and see if the level drops, if it does, add antifreeze till full, put cap back on - Find and repair leak!

2 - Check water pump belt, tighten or replace if needed.

3- With the car warmed up find the 2 hoses leading to the firewall and the heater core. Turn on the heater and feel both hoses if one is hot and the other is cold the coolant is not flowing. Check to see if you have a valve with a vacuum hose on one of the heater hoses. Feel the hose before and after the valve if the engine side is hot and the other side is cold replace or repair valve (may only be bad vacuum line to valve). If both sides are hot then you have a bad/clogged heater core. To try an fix it, remove both hoses and run a garden hose into one of the hoses to see if water will flow, if no flow or little flow, flush the core both directions until clear and reassemble.

A bad or leaking heater core will steam your windshield and cause a god awful smell.

Let me know your results,
Hawk,