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Discussion Starter · #1 ·
Hey. i'm shooting this question out there for anybody who's had this problem before. i have a 1988 5.0 stang and my situation is as follows. I had absolutely NO heat in my car at all. heater blows at full speed but blows out ICE cold air. no defrost. nothing. pain in the ass getting to work in the morning. Well, my first thought was the thermostat. I replaced the thermostat and low and behold, i have nice hot heat after the car warms up. Well, then i realized that i have hot heat until i start to go to work heading on I-20 going about 70 or 80 and the heat drops down to ice cold again. when i get into town and slow down, the heat returns. Only when i do highway speeds does the heat drop down to ice. what causes this? I also have a slight leak at the water pump. (bearing's shot, i think) could it be the restrictor in the heater core hose going bad? (if that's possible). caused by air in the system from water pump leak? blend door? (the cable looks fine from behind glovebox. any checks i can do or things i can check out? it would be GREATLY appreciated! thanks again!!

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What is the engine coolant temp./gauge doing during all of this? Are there any other drivability issues?
 

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Discussion Starter · #3 ·
not that i'm aware of. engine temp appears to be fine. sits about the half way point between cold and hot. no MAJOR symptoms i'm aware of. just leaking coolant out of the pump a little. a slight bucking when going uphill in 5th gear. But that's unrelated. i chaulk that up to POS Borg-Warner T5 Tranny. i'm thinking maybe no restrictor in heater core inlet hose??? the only time i feel it is when i'm going highway speeds. maybe? not sure..someone told me when the water pump is leaking, it causes air pockets in the coolant system and there could be air trapped in the heater core but i doubt that due to the fact that i have nice heat once i warm up and am driving around town. thanks though. i wish i could fix it b/c most of my driving is on the highway going 70-90. thanks again.
 

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Discussion Starter · #4 ·
anybody had this problem before? is it a missing restrictor in the heater core hose???
 

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How fast is the engine turning over during highway driving? Versus average speed driving around town?
 

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having no restrictor wouldn't hurt the heat, it just builds pressure in the core and will bust it quicker....sounds like you might have a clog?

possibly a break in the line somewhere and air is being introduced causing steam and air pockets in the core?
 

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My car behaves a a similar manner, warming up over the first five minutes of driving (with corresponding heat and temp gauge needle at about 3/8) then the air from the heater cools off a ton. My theory is that the heat comes on as the engines warms up, with lots of warm air from the vent, then the thermostat opens and cools the engine down with more water passing through the radiator. This effectively kills the heat coming into the interior until enough heat builds in the system to heat up the fluid in both the engine and the radiator. Basically, when the thermostat opens, it allows the fluid to cool too much to provide good heat. Sounds to me like this is what's happening when you get good airflow across your rad on the highway. Only solution I can think of is to block off part of the rad like truckers do (?). WOuldn't hurt to try it as long as you keep an eye on the gauge! -Boozer
 

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My guess is that one of the flaps is stuck partially open that regulates fresh outside air vs recirculated air. At low speeds the heater can handle it, once you hit the highway there's just too much air being forced in to heat.

Check and make sure all your vacuum doors are opening/closing.
 

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when my 93 was losing coolant and the radiator level dropped a ways my car did the same thing no heat just cold air, after the leaking heater core was replaced end of problem
 

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I think DOKTOR (appropriate it seems) has offered up what may be the problem. Mfalcon - mine doesn't act the way yours does.
 

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I would suggest that you check the condition of your engine coolant. You mention that your water pump is leaking. When you fill the system back up...Do you add antifreeze & water or just water?

It could be possibe that as you drive at highway speeds the coolant in the radiator will freeze causing the coolant flow through the engine to be reduced or eliminated.

I had a simial situation when it was very cold and had the same symptoms except the engine also overheated after about five min.

Just a thought...Hope you get the problem resolved!
 

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Runin1320 suggests a problem that is common when the coolant mixture is less than 50% antifreeze/water and happens more than you might think.
 

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You have to be quite low on antifreeze - I intentionally run about 35% antifreeze/65% water, and mines protected to -10F (checked with specific gravity tester). And, if the water were gonna freeze, it would have frozen in the radiator before he ever started to drive. "Wind chill" effect is only an issue for humans experiencing cold temps and wind; a radiator won't cool a fluid to any lower a temperature than the ambient temperature flowing over it - no matter how fast the air's moving across it.
 

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Equal concerns for me are not only the freezing/slushing of the coolant but, the anti-rust/corrosion inhibiting qualities of having a 50% mix.

True - antifreeze does not lose it capability of protecting against freeze up's but, it DOES LOSE is effectiviness to prevent rust/corrosion.

True - VERY FEW people change their coolant when it needs to be. If they did there would be FEW radiators, heater cores and frost plugs replaced.

False - The amount of air moving across the radiator is not important in cooling and how fast it cools. If this were true - then you would not need a fan? As a matter of fact: Electric fans are used increasingly because many times they are not needed when travelling at speeds over 35 MPH.

Believe it or not.
 

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Discussion Starter · #15 ·
thanks for the help

Thanks everybody for the help! I gotta give it up for all the other fox-body stang DAILY drivers like myself. thanks guys. i'll check it out.
 

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bronzesink - you misquoted and misunderstood me. I didn't say the amount of air moving across the radiator is not important in how fast it cools or the amount of cooling (the amount of heat transferred). It clearly is. I said you can't cool a fluid in a radiator to a lower temperature than the ambient temp of the air moving across it. One of the previous posters mentioned that once the car was moving lots of air across the radiator perhaps it was getting cooler and then would freeze. If it's 20F degrees outside, the water/coolant in the radiator won't go below 20F degrees whether the car's sitting still or moving at 100 mph. You will remove heat more quickly if more air's moving across the radiator, but no matter how much/how quickly the air's moving, you won't cool it below the ambient temp. So, if it was cold enough to freeze it, it would likely have frozen the night before while sitting still - before ever being started up.
 

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Michael: Yes I did - i apologize.

Have run across a few that had a low % mix - parked in a garage where the temp was warmer - took the vehicle out on a morning, when the temp had dropped well below freezing, (usually one of the first of the season), and froze/slushed the radiator causing the engine to overheat.
 

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Yup - I can see that happening. Guess I've lived in mild enough climates most of my life that you've got to try pretty hard to freeze one up. Course, I've been blessed with (and perhaps taking for granted) garages for a number of years. The only time I had to worry about it was a race car years back where, of course, it was illegal to run antifreeze (they don't take kindly to the slippery stuff spilling on the track). So I'd have to remember to charge it up for a couple of months in the winter. But it was Houston -- not much of a winter.
 

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I had this exact problem, take your glove box out and yuo will locate a cable it is the one on the lower left of the hear box, now while lookign at it reach up and move the heat knob on yoru dash from cold to hot, see any movement? you may either have a broken cable or if it is the same as my case the cable came off the adjuster clip. to put it back on pop the adjuster clip off of the heater core door lever and install it back onto the cable, there should be 1" of cable sticking past the edge of the adjuster clip. the haynes and chiltons manueks both show this. It's a 10 minute fix. your glove box is held in by 2 screws at the bottom edge.
 

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Instead of replacing coolant I thought you can just replenish the corrosion inhibition additives (and cavitation protection additives for diesels)... Makes more sense than junking antifreeze.
 
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