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Sudden blend door failure?

Melon

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00 5.0, no heat. Gut says blend door. Brain says otherwise because I never heard gears clicking like I did in my 94 Thunderbird. I had good heat, then it sat for a while (tierod end and I was an idiot) back together and barely had heat and then just cold air. At the same time, discovered a leak in the radiator so replaced with a new one, hoping low coolant was the culprit, but I don't think that's the cause. I didn't flush the system at the time, but is on my to do list sooner than later.

Is the blend door that weak and go out that quick? I saw a video from 1A Auto and it looks easy and straightforward to change. I also need to feel the heater core hoses next time I'm near it and let it run again. Am I missing anything else?
 


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Gary Crist

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A stuck open thermostat will cause your problem (had that problem on my 91).
One of those infrared temp readers would be nice.
Also, after it is warmed up, check the temp of the upper
radiator 1st. If it is only warm, then the engine will never get enough hot
water to you.
 




Melon

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That may explain why one end of the upper radiator hose was warm and the other side was cold? The temp gauge was showing normal - take that for what its worth :) if I remember right, I think the radiator side was cool and engine side was warm.
 








Melon

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Thank you :)

Glad I didn't follow my gut on that one. Looks like I'm stopping by the parts store for a thermostat. And then kicking myself for not changing it while I was changing the radiator :)
 




Turdle

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Also, take a close look at the coolant bypass valve position. Run ac on cold, look at bypass valve, turn on heat and floor vent then take note again of position of valve. Also take note of blend door noises as the blend door will only move when the temperature is adjusted.
You might also check the vacuum which powers the bypass valve. Sometimes the feed line will get melted shut, or, cut in 2.
Low coolant level will result in no heat


I might be off base, however, If the temp gauge was in the middle of normal, it does not sound to me like a stuck open thermostat. Stuck open it would barely move off the bottom.
 




Melon

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I assume the bypass valve is inline with the heater core hoses? I'll try flipping the temperature and listen for the door as well. While low coolant may have originally contributed to it, I don't think it's the root cause.
 




Melon

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What about if theres still air in the system? On my Thunderbird, there's a bleeder valve for it. I don't recall seeing one on the Explorer?
 




Turdle

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If you can, park on an uphill incline or raise the front of explorer enough to get the radiator cap higher than the heater core , run engine until hot and allow to cool. While cooling any air should bubble into the reservoir. I do not recommend removing a radiator cap when hot, but after a while pressure should be down enough to release the pressure by twisting it a tad. bubbles will flow into the overflow . Once pressure is released refill radiator. top off reservoir and repeat until no bubbles are observed.

Also, the overflow reservoir must be clean clean. The tube to the radiator is on the bottom so any debris will act as a one way valve which will block coolant flow back into radiator.
Pressure from radiator will overcome this blockage and allow coolant into the reservoir. Over time the radiator level could go down if this blockage occurs.
 




Melon

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I've got a pair of ramps that should do the trick.

Just run the engine up to operating temp and then let it cool with the nose in the air? For some reason, I was expecting something more involved. The hardest part will be watching for bubbles. Thank you :)
 




Turdle

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I forgot to mention turning the HVAC on floor, temp to hi . Feel for hot heater core hoses also.
 




Melon

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Remember when I said I was sure it was full. I was wrong :) I looked up radiator capacity (because of course I think of this when I'm no where close to the vehicle) and it says it takes almost 4 gallons.

Does the radiator really hold that much? I didn't think I drained 4 gallons out when I changed the radiator.
 








koda2000

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The total coolant capacity may be around 4.0 gals (I haven't looked it up), but that includes the engine block, heater core and hoses. There's no way to drain the 100% of the coolant out of the engine block or heater core so you'd never get all the old coolant out. IIRC after flushing I put in about a gal of concentrated anti-freeze and fill the radiator with a water to achieve a 50/50 mix, which (after mixing) is good to around -34 degrees according to my anti-freeze tester. So 2-2.5 gals on a refill seems about right.

When you get a leak anywhere in the cooling system you can't go by looking at the coolant level in expansion tank because the coolant will not be drawn from the expansion tank if the system has a place to suck air from. When cool, check your coolant level in the radiator to know for sure if you've lost coolant. Also, the hose from the radiator to the expansion tank can become clogged and then the radiator can't draw from the tank.

Your description of "sudden blend door failure" makes me scratch my head. If your blend door stops working/breaks that would not make it an "intermittent" problem. If the gears in the blend door actuator strip (a fairly common problem) that would be the only time you'd hear a clunking noise along with loss of temp control. If the blend door actuator's electric motor stops working you would loose heat control with no noise, if the blend door itself breaks (another common issue) it will happen "suddenly". All of these things would be sudden and not be intermittent. If your heater control valve fails it can also stop hot water from flowing through the heater core.

You say you were wrong about having low coolant. If you're loosing coolant the first place you may notice a problem is a loss of interior heat because hot water stops flowing to the heater core. You may also see that your temp gauge registers colder than normal because the gauge's sender is no longer submerged in coolant.
 




Melon

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I had a feeling the 4 gallons was overall capacity and not just the radiator. I'm going to get another gallon and see how far it gets me. I haven't been going off the level in the tank, each time I've been popping the cap itself.

For the blend door, I never heard any clicking to make me think stripped gears. The blend door actuator failed on my Thunderbird and that clicked for a long time before completing failing. I currently have no heat whatsoever.

My plan for Sunday is to top off the radiator and get it up to operating temperature. Once there, I'm going to change the temp on the climate control from cold to hot and listen for the door. And while I'm there, I'm going to check the heater control valve as well. And after it cools, verify the level again.
 




koda2000

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I had a feeling the 4 gallons was overall capacity and not just the radiator. I'm going to get another gallon and see how far it gets me. I haven't been going off the level in the tank, each time I've been popping the cap itself.

For the blend door, I never heard any clicking to make me think stripped gears. The blend door actuator failed on my Thunderbird and that clicked for a long time before completing failing. I currently have no heat whatsoever.

My plan for Sunday is to top off the radiator and get it up to operating temperature. Once there, I'm going to change the temp on the climate control from cold to hot and listen for the door. And while I'm there, I'm going to check the heater control valve as well. And after it cools, verify the level again.

Once warmed up, with the temp turned up to max, check the difference between in and out hoses to the heater core. They should both be hot/warm if water is flowing through the heater core. If both hoses are hot and you're still not getting any heat in the cabin, either the blend door is broken, or the actuator is not working. With the engine off key on, if you vary the temp setting you should be able to hear the actuator working and feel it working if you place your fingers on it. To prove the blend door is broken, I have taken the actuator apart, removed the crescent shaped gear, inserted it into the heater box and moved the blend door open/closed by hand. If the door is broken the crescent gear will just spin.
 




Melon

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I believe the culprit is the little electric motor inside the actuator. I removed the actuator and took out the moon shaped gear. The blend door moves freely with gear shaft in its spot.

I was going to take it back out and leave it in the glove box for the time being - you know, for Mother Nature temperature swings in March - and it slipped and fell back behind everything and who knows where it went. Thankfully it's on hot side so I should be good to go.

Thank you for the suggestions along the way. Its great being able to bounce ideas around.
 




koda2000

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Sharing wisdom is the whole purpose of this forum. I installed a Dorman blend door actuator in my 2001 EB about a year ago. I don't like Dorman stuff, but for around $4, using some Amazon points I had, I figured I'd give it a try. It was a bit fiddly to install, but it's still working okay. Someone here suggested taking the guts out of the Dorman unit and installing them in the broken OE actuator.

Do you have the manual or EATC HVAC controls? The actuators look the same but are different under the cover and are not interchangeable. If you have the EATC controls you will probably need to reset the EATC module, by running the EATC self test (Google it) before the replacement actuator will work.

I know what it's like loosing things (like screws) in the black-hole behind the heater box.
BTW - don't bother trying to get the rear mounting screw back in. It's very hard to do and not necessary. I believe the replacement Dorman actuators come mounted to a snap-on plastic base, but I removed the base and reinstalled the actuator with 2 screws. I think someone here said you can just snap the base onto the heater box and be done, but IDK.
 




RickOTR

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The radiator on my Sport takes 19L or about 2.25 gallons. Just flushed it yesterday along with replacing all the Rad and heater hoses...

When my blend door broke I just bought the door from Ford for about $20 and just unsnapped the old one and snapped the new one in place instead of cutting up the plenum. Had the take out the evaporator core though to install it. Still easier than replacing the whole plenum.
 


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Melon

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I have the manual controls, I've never been a real fan of EATCs. I forget the brand, but its $30 from RockAuto. And I already wasn't planning to put the back bolt back in. It was "fun" getting it out, I'd rather not have to put it back in :) the hardest part will be lining up the shaft, so to speak.
 




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