Heat never hot!!!

2001 4 cyl 2.3

Last night was the first night in months its gotten a bit cold. Imagine my surprise that I turned the selector to heat, and received NO HEAT.

Did a bit of research today and found this to be a somewhat common problem to this engine, although the solutions range from the strange thermostat\all in one\ too expensive housing, the water pump, to a clogged heater core.

Just got done putting a large amount of money in this thing's suspension so I'm looking to try to fix this one myself.

I noticed last night that the heat would change from lukewarm to cold consistently in a matter of minutes, with the temp gauge changing from a little hot to normal at the same rate.

This morning I did some testing and while I could never get the temp gauge to waiver from normal, I never got warm air out of the heat setting.

I've posted some pics of the cooling system with some general layout questions as well as questions about the layout coming off of the upper radiator hose to the heater core.

I noticed that once at operating temp, some hoses seemed to be cooler than they should be going to the heater core.
(Please see pics)

Any ideas off hand? (I'll post some pics of further investigation in a bit.)

Thanks for any help....

If it is a thermostat issue the dash board gauge will show cooler engine temp.
T-stats tend to fail Open, so engine never heats up.

There are three types of heater systems.
1. two hoses from water pump and intake manifold to heater core, coolant is always flowing thru these hoses, the Blend door inside controls the heat coming out.
The heater core in this setup is part of the cooling system, if blocked or partially clogged temp gauge will show random spikes in temp, not overheating but heating up past normal then down to normal.

2. two hoses from water pump and intake manifold to heater core, but 1 hose has a valve on it, the valve can either be vacuum or cable operated, this valve controls the flow of coolant thru the heater core, so controls it's temp.
This will have a separate by-pass hose.

3. by-pass system, it has 4 hoses, 2 from heater core, 2 from engine.
This will have the same type of valve setup as #2 but is also part of the cooling system in that the by-pass is required for water pump circulation.

Looks like you have #3 and it is vacuum operated.

The by-pass will have 4 hose connections and a valve, try to manually operate the valve.
If valve is sticky or stuck then hot coolant won't flow fast enough to keep the core hot when heater fan is on, so you would get some heat at first then it would cool off.

RonD said:

The by-pass will have 4 hose connections and a valve, try to manually operate the valve.
If valve is sticky or stuck then hot coolant won't flow fast enough to keep the core hot when heater fan is on, so you would get some heat at first then it would cool off.

Click to expand...

Based on your info, I'm leaning more toward the valve or water pump more than the Tstat at this point.

How do I manually operate the valve?

Should the valve have vacuum when the heater is on or off?

How much vacuum should operate the valve?


Thanks for the help.

In relation to your picture...

"This" is the heater bypass valve. The line on it goes to the intake, via a solenoid controlled by the HVAC head I believe.

It is quite common for them to get stuck closed during the summer months, which would roughly produce the current listed status of the heater hoses in your picture. The two coming from the engine are hot, the two going to the core are cold because they are out of the loop. This is probably the source of your lack of heat. If it was me I would just go get some barb fittings and clamps and bypass it. It's just there to shut off flow to the heater while the air conditioning is on.

Also, for future reference - I figure I may as well address your pictures. The first picture is of your HCV (heater control valve). The grey vacuum line comes off of it and connects to the HVAC harness below the heater box on the passenger side. If you pull the passenger side carpet, or more likely rubber mat, you will see 2 vacuum lines coming trough. I would assume that your valve is blocked as well considering you're listing two of the lines as 'cold.' The new switches are fairly cheap (I think I paid $20 or $30 for mine at O'Reilly) and very easy to replace. I wouldn't think you have a vacuum leak or anything that because you haven't described a defrost lock at all.
In your second picture, you are looking at the thermostat housing but with the engine heating up normally, this isn't your problem so don't worry about it right now.
And finally, the third picture is the water pump pulley. I also do not think your water pump is causing the problem. There may be a slight chance that it is but I personally would not pursue this as a cause.

Best of luck.

Rangurr

Thanks to all for your replies...

OK update.

I have taken a closer look at the heater bypass valve and vacuum hose.

Based on what I can tell the vacuum switch and armature are working normally....
Vacuum present when A/C is on and the armature is pulled up.
Vacuum not present when heat on and the armature is pulled down due to the spring.

The only possibilities I can see of the heater bypass valve being bad is if there is an obstruction somewhere in the unit or the internal "door" has somehow broken loose or malfunctioned.

Anyway, something else I noticed.... When I turn the heater on and select the "Vent toward occupant" option, I will get "somewhat" lukewarm air, but when I select "defrost" the air gets almost cold. Select it back to vent, slowly warms to lukewarm.... very, very, weird.

I will go ahead and replace the bypass valve during the week due to the ease of the replacement, but if it does not solve the problem, the only other thing I can think of is water pump or heater core, of which I am receiving none of the standard symptoms for either being bad.

What are the easiest ways to check for blockages in the heater core or a low output from the water pump?

Also, where is the weep hole on the water pump? Is there one?

Thanks for all the help!

I suppose it could be worth your time to try and back-flush your heater core. Pull the two hoses and replace with some decent length pieces of hose. Then use a garden hose to flush the core, switching back and forth between the two hoses. If anything is resisting flow, you should be able to work it out using this method. If you are unable to restore un-blocked flow, it's time for a new heater core... That job is never fun -_-
There is a weep hole on your water pump, it's located on the lower side behind the pulley.

Simple test is to "open" the by-pass valve allowing warm coolant to flow thru the heater core, feel the IN hose it should start getting warmer when valve opens, then OUT hose will start to warm up if core is passing warm coolant.
Make sure Blower is off, turn Heat to HOT, heater hoses should start to heat up very fast if coolant is flowing.
Engine warmed up and running of course

Finding out which hose is IN and which is OUT is important if you want to backflush the heater core.

If the IN and OUT hose both warm up then your problem is at the "Blend Door" inside the dash, the blend door moves to direct heat inside and to selected vents.

Sorry for the long pause guys... work has interfered with my "truck" stuff.

Anyway, via the last post, the heater bypass valve seems to work correct and the heater works "sporadically", but more not work than work.

I can turn the heater control to on, the vacuum will cease on the bypass valve (or I can just unplug the vacuum tube) and it will remain Ice cold for 5 minutes, then start to warm up for one minute, then go ice cold again.

So the bypass valve IS working, and the heater core DOES seem to work when it gets hot coolant.

The Temp gauge varies from from running a little hot when the air is cold, and then the temp gauge goes back to normal temporarily when I start to get warm air.... until it goes cold again.

Are we thinking the water pump or the thermostat assembly being the culprit here?

Is it worth the 20 bucks to replace the bypass valve anyway?

i bet the t-stat is stuck open. if the t-stat was stuck closed or the water pump wasnt pumping, you'd be overheating. t-stat is also the cheapest place to start.

Gargamel said:

Sorry for the long pause guys... work has interfered with my "truck" stuff.

Anyway, via the last post, the heater bypass valve seems to work correct and the heater works "sporadically", but more not work than work.

I can turn the heater control to on, the vacuum will cease on the bypass valve (or I can just unplug the vacuum tube) and it will remain Ice cold for 5 minutes, then start to warm up for one minute, then go ice cold again.

So the bypass valve IS working, and the heater core DOES seem to work when it gets hot coolant.

The Temp gauge varies from from running a little hot when the air is cold, and then the temp gauge goes back to normal temporarily when I start to get warm air.... until it goes cold again.

Are we thinking the water pump or the thermostat assembly being the culprit here?

Is it worth the 20 bucks to replace the bypass valve anyway?

Click to expand...

Yes, could be thermostat but that wouldn't account for up and down temp gauge, stuck open would be steady...cold.

It really reads like there is air in the system, by-pass is usually one of the higher points in the cooling system, so a natural air trap.
Air can block coolant flow, an air lock, this would cause the temp gauge to rise a bit and then changes in RPM can break the air lock so heater gets warm as coolant flows and temp gauge goes down.
Then it repeats.
A loose by-pass valve can act the same, blocking flow like an air lock, then opening again, so up and down temp.

With engine cold I would remove rad cap then disconnect the highest heater hose, fill it with coolant or distill water, both ends, if its not full already, if there is no sign of an air bubble then you may need to pull out the by-pass and inspect it better, make sure valve is not loose.
Then reconnect trying to keep air out.

Now remove the Overflow hose from the rad cap opening, blow into it to make sure tank end isn't clogged up, debris in the tank can settle at the bottom and block coolant from returning to rad, so air can get sucked in instead.
If blowing in the hose feels hard, get out the garden hose and flush out the overflow tank, watch what drains out the hose.
Check the overflow hose for cracks/leaks as well, air is easier to suck back in than coolant.

If it all checks out, put overflow hose back in place, top up rad if needed, replace cap.

Start engine, and feel heater hoses, they should start to warm up right away.
But Upper Rad hose should not, upper rad hose should not get warm/hot until engine coolant gets up to 200 degrees, usually from 5 to 8 minutes.
If it warms up sooner the t-stat is indeed open.