temp gauge doesn't register, no heat

[AMC lifer]

The temp. gauge appears to have quit working, or at least doesn't register any temp. The heater output is almost nil. However, it does put out heat after approx 1/2 hour of running.  This is during 50 -60 degree weather.  I have replaced the thermostat twice as I thought I got a bad one. I did discover that the lower radiator hose was leaking.

These hoses have been replaced:
     Upper & lower radiator hoses - mushy on the engine side.  No current leaks after replacement. Upper get hot as it
        should, don't know about the lower hose, I did not check.
     3/4" hose from the water pump to the heater valve - no leaks but doesn't get real warm.
     5/8" hose from engine to thermostat housing - does get hot as it should.

The heater hose at the back of the engine also get hot as it should.

The antifreeze is at normal level.

What could be the issue?

blocked heater core?
bad water pump?
bad heater control valve?

Does the Temp sensor have to be operational for heat to get to the heater?

[mudkicker715]

At the back ds near firewall is a stud/post a single wire might have fallen off of.

[Hawk258]

Sounds like you have a clog in your heater core And either the sending unit is bad or the gauge just quit. and or what he said ^^^^^

[Jurjen]

You can try grouding the wire from the sending unit, it should give full read out.

Was the heat OK before you worked on the cooling system?
If so, some air maybe trapped near the heater matrix.
You could try cracking one of the heater hoses near the firewall (with a warm and running engine).
Eagles with an A/C also have a heater valve near the fire wall, that may be stuck too, but is mormally stuck in the full open position.
A clogged heater matrix is a common problem on the Eagle.
Normally it needs to be replaced.
Prepare yourself for a day full of blood and adventure.

[AMC lifer]

Thanks for the information. Since we are just now into the season for the need of the heater again, I don't know how long it hasn't been putting out heat. It did work last spring when I needed it.

I have replaced the heater the heater valve several years ago when it began to leak.

Jurjen, I am assuming when you say heater matrix you are talking about the heater core.

Mudkicker, thanks for letting me know the location of the temp sening unit.

Why don't I find these things out when it is nice weather instead of cool fal weather. I don't have a place to do the work except outside in the backyard

[Hawk258]

AMCer, You bring up an interesting point, we don't think about certain things till we need them.

[Jurjen]

Yes, I mean heater core, our UK friends use "heater matrix" for the same thing.
Maybe it is just air, you can just try and burp the system.
I should put out a lot of heat, even when it is freezing I have to adjust it near the "cold" setting.

[ammachine390]

I would try back flushing the heater core. Take off the two hoses, and run your garden hose to into the outlet. I did this once, and used a milk jug to catch the coolant that came out. After about a day, all the sediment in the coolant settled, and the heater worked a lot better. The next year, I had to do it again though, so you may think about a total cooling system flush.

[AMC lifer]

An update on the progress? 

After replacing the bothradiator hoses & several heater hoses & the thermostat twice, I do get SOME heat, it does take longer than it should though.  The temp guage still does not work.

Considering the weather, & the lack of an indoor area to work, I have decided to take it to my favorite mechanic & have him get it going if possible. I noticed a dribble of antifreeze on the grould at the front end after the car was shut off. It could be that I didn't get the upper part of the lower hose tight enough or it could be a water pump leak. Normally I could do this but I will pay someone instead of standing out in 45 degree weather with a 25 mile per hour wind blowing.  That is for the forcast in my area.  The next week looks like it could get cooler & snow. I definitly want heat/defrost then. I will post any findings after he works on it. unless it is something more major (engine wise).

[Hawk258]

when you refilled your coolant did you put the car on ramps so the radiator tips up? Sometimes air gets trapped in the system and causes issues. Also I might suggest checking the water pump and thermostat as if the thermostat is stuck open the water won't warm and cool properly.

[jim]

Did you check the wire on the sending unit that mudkicker mentioned?  I sometimes knock mine off when messing around in that area.  It's somewhat hard to see with all that tangle of hoses and wires in the way.  That's very often the cause when the gauge does not move at all.

[AMC lifer]

No, the car was on level ground at all times.

I would try to flush out the heater core, but one little problem, no outside water hookups.  As I stateed earlier, I only have the outside backyard to work in.  Considering the age of our cars, I would not doubt if there is much gunk built up. I wish they would have taken a lesson from Jeep & put the core under the hood.  Heck my old '78 Ford LDT had the core under the hood.  five screws to remove a cover & the core lifted out.  It took longer to drain the radiator than it did to remove that core.  I'm sure my mechanic will try a flush first rather than tackle a removal.  It takes less time.

Yes I did see the stud at the rear of the engine with the wire on it. I took the wire off & put it back on as it did feel as if it were not on tight. Current weather outside is 50* with a wind of 20-25 with gusts of 30 mph.  No wind block available, much dust/dirt blowing around.

The car goes to the shop on 11/9/11 so I wil find out what is going on then.

[Hawk258]

Well, Glad to hear you are taking her in for a doctors visit, Good luck.

 As for "Gunk" most of our older cars weren't designed to deal with the anti-freeze they have today, I recommend a regular flushing, and I am not 100% but I have seen many comments to the effect when people are complaining about overheating on pre-85 vehicles, Though keep in mind this is also untested by me. Though, I would not be surprised either way if it was true or not. Though I think I will play devils advocate and Say it might be a "Bit" expensive, but in the long run Probably in our best interests as I am sure we don't want to test that theory and find it is true. though, I am sure if you are planning a 4.0 H.O. Upgrade, and need an excuse.

 but that's just my 2 cents.

[carnuck]

Don't use the red antifreeze in your Eagle! It accelerates breakdown and even GM lost millions in the lawsuit over it causing damage!
http://www.stuevesiegel.com/CM/Results/NATIONWIDE-SETTLEMENT-REACHED-IN-GM-DEX-COOL-CLASS-ACTION-LAWSUIT.asp

[BenM]

After dealing with gunk in the coolant on my cars, I switched back to the old-fashioned Green coolant. The "All Makes, All Models" extended life coolant always formed gunk in my overflow tank. The OAT coolants are harder on lead solder and more likely to cavitate, as well as forming gunk in overflows. The green stuff never does that.

I never go two years without doing something so it doesn't bother me.

You could also try flushing your cooling system with vinegar to remove mineral deposits. Don't leave it in too long, it will eventually start attacking metal, just add some, run it, and then flush. I was recently reminded about vinegar looking at de-rusting preparations over the weekend.