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Discussion Starter #1
Need a bit of help narrowing the issue here. My '95 Bird has been running trouble-free for years now, and yesterday morning was a bit chilly outside so I cranked the thermostat up to 85 to warm things up. All I got was cold air. For reference my commute is 20 highway miles, plenty of time for the engine to get fully warm. The other unusual thing I noticed is that the temp gauge does not show the car as fully heating up. Under normal circumstances the temp gauge stops to rest on the right side of the "N" in 'NORM'. The past two days driving into work the needle doesn't make it to the left side of the "N". I know these are idiot gauges, but the temp gauge is always more accurate/responsive than the oil gauge, etc.

One other thing I'm aware of is I do have a slow coolant leak that's been ongoing for a while, but my work schedule (traveling a LOT) hasn't allowed me to get it on a lift yet to pinpoint the leak.

I can think of a couple things that could be wrong here, but need some guidance to narrow down the real culprit.

Possible issues:

1) heater core shot
2) blend door actuator shot/stuck
3) faulty thermostat
4) faulty engine temp/coolant sensor(s)

Any advice on what I need to look for to trace this no-heat issue is greatly appreciated.

Thanks,

Jon
 

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You listed everything except the most obvious. The fluid level in the radiator. Too low, no heat. If your level is right and you have the right blend of antifreeze then you should get some heat, barring the other things you listed. If you have the auto system. Set it to manual. Stop car, turn off ignition.Wait 10 seconds or so, fire it up drive a few hundred yards, turn the fan speed swithc to about halfway and see if it doesn't blow warm air through the vents, If it does, then move the switch to floor or whatever. I went through everything you're going through when I lived in Florida on cold days. And, yes, it does get damn cold sometimes even in Sarasota. Now, living in Maine....burrrr!
 

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I would start by checking the coolant level and, if that's O.K., then try replacing the thermostat next. I don't think that a faulty engine temp sensor would affect whether or not you're getting heat from your heater, but it could definitely affect how the gauge is reading (I'm talking about the sensor for the gauge; the other sensor is for the engine control computer).

Good luck!

Dennis
 

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Discussion Starter #4
Thanks for the quick replies guys. Should have stated in the first post that coolant is full and is a 50/50 blend with water. Due to the slow leak I check and top off approx. once per week.

Will be sure to set thermo to manual, and failing that I suppose thermostat is the next (and fortunately cheapest) next step.
 

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You just need to feel your heater hoses and see if they are hot with the engine warmed up. That will let you know if you have a circulation problem. If it is hot, then yes you should start looking towards the blend door actuator/control switch problem. If the hoses never/take forever get hot and the level is good for sure, your thermostat may be stuck open.
-Rob
 

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Due to the slow leak I check and top off approx. once per week.
There is very likely an air bubble in the crossover in the manifold.

No water flow, no sensor action.

Since the eec uses one of these, it will cause problems sooner or later.

Check the rear of the intake at cylinders 7 & 8; that's where my slow leak was.
 

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Discussion Starter #8
a bad head gasket will suck coolant out and leave you with air.
Yes, but there'd be other signs than just what I'm seeing here I'd expect. Plus I've got a 4.6. If it was the 3.8 I'd be worried.
 

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First thing I'd do is check the thermostat - since you say the temp gauge stays low and you're not getting much heat.

Also check the lines to the core like Grog suggested. At least that way you'll know if it's the same temperature as the engine.

As far as air bubbles, my only experience with one was accompanied by the temp. gauge climbing slowly up to operating temperature, then climbing up near 3/4 rather quickly, then suddenly dropping back down to operating temperature. My inference is steam under pressure in the crossover took longer than pure coolant to get the thermostat opened.
 

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Raoul Duke
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Run a diagnostic (search) on the SATC system to see if there is a fault with the blend door. Mine acted up two winters ago and gave me only cold air. It eventually fixed itself and I have heat again, but I'm waiting for it to fail entirely.
 

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Discussion Starter #12
Thanks for the responses so far guys. I've finally got a day off tomorrow and am going to run out and get a new thermostat asap. Will update after installation.
 
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