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DOHC - 2.3L Duratec / Mazda L Engines Discussions and Topics specific to the Duratec 4 cylinder engines

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  #1  
Old 11-09-2015
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No heat in the cab when the engine is warmed up

hey guys for the past couple of months I've been living with no heater but now that its starting to get cold and the windows fog up i need my heater to work. even if the engine is completely warmed up it still just blows cold air. I've done a little research and it seems like it could be a number of different things and I'm not sure how to narrow it down. I talked to a guy at pep boys and he said that it could be the fan thats stuck or broken. apparently this fan is inside the dash and i'll probably have to remove the dash if i want to fix it. personally, i doubt it could be this fan since the vent and ac still blows air. he also said to check my fuses. all my fuses looked fine. i'd really like to fix this since football seasons over i need a project lol any help or advice would be much appreciated thanks!!!!
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Old 11-09-2015
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In the engine compartment, on passenger side, there will be 2 hoses going into the firewall, they attach to the heater core inside cab and warm engine coolant should flow thru the core when Heat is selected on the temp control

After engine is warmed up, turn heat to HOT inside and leave engine running, feel both hoses, see if one is warm and the other cold or both cold.

Follow the hoses back towards the engine, you will find a valve with 2 or 4 hoses connected, this is the heat control valve, it is activated by vacuum, but you can often move the valve arm using your finger.
Try moving it then feel if the hoses are warming up.
If it won't move pull off vacuum hose and see if vacuum is present, if so then valve is probably broken, try moving it again, it should not be hard to move at all.

If valve moves and hoses get warm then make sure vacuum is good, should hold finger tight, if no vacuum then could be a few things, check back if thats the case.

If valve and vacuum seem OK and one hose warms up a bit but the others stays cold then you could have a clogged heater core.

You can Back Flush heater core to try and get it cleaned out.
Google: back flush heater core

Lots of videos and pics of how to do it, it isn't model specific, they all work the same way.

Last edited by RonD; 11-09-2015 at 11:05 PM.
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Old 11-10-2015
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look up blend door on here lots of posts about it
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Old 11-11-2015
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I am having issues as well, I have flushed my heater core, but the only issue that I am having, is that when I disconnected the inlet hose to the heater control valve and thurned the engine on and had the heat set to hot, I had no fluid actually come out of the hose. SO I am wondering why I am not getting any fluid to my heater core.
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Old 11-11-2015
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Valve is bad or hose could be blocked
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Old 11-14-2015
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Quote:
Originally Posted by thatoneguy93 View Post
I am having issues as well, I have flushed my heater core, but the only issue that I am having, is that when I disconnected the inlet hose to the heater control valve and thurned the engine on and had the heat set to hot, I had no fluid actually come out of the hose. SO I am wondering why I am not getting any fluid to my heater core.
The 4 port valve is vacuum controlled. Vacuum is applied in the MAX A/C and OFF positions. When vacuum is applied the valve closes off the heater core and diverts fluid back to the engine.

Are you low on fluid?

To check the valve look at the metal arm opposite of where the vacuum line connects to the valve and have someone turn the vehicle from OFF to VENT. You should see the arm move.



To check the blend door drop the glove box and locate the blend door actuator on top of the HVAC box. you will need a "mirror on a stick". There is a 1/4" square hole on the top. move the blend **** form cold to hot to cold and see fi this square hole rotates. If not its your blend door actuator.

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Old 11-16-2015
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ok so I've come to the conclusion that its not the vacuum (works just fine) and the two hoses get hot. so its gotta be the blend door. but the blend door is behind the stereo right? if I'm understanding this right then the blend door is behind the stereo and the actuator is behind the glove box? MORE PICS! thanks!
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Old 11-16-2015
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Originally Posted by Bazman2008Ranger View Post
ok so I've come to the conclusion that its not the vacuum (works just fine) and the two hoses get hot. so its gotta be the blend door. but the blend door is behind the stereo right? if I'm understanding this right then the blend door is behind the stereo and the actuator is behind the glove box? MORE PICS! thanks!
Blend door actuator is on top of the HVAC box behind the glove box. Inside the black box below it is the blend door. The blend door is sealed in the box.

The white box in front of his ring finger is the actuator.


This is what the blend door looks like. You will never be able to see this unless you dremel the box open.

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Old 11-17-2015
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ok so getting to the blend door isn't as hard as i thought it would be. i'll see if i can get to it this weekend maybe and then i'll let you guys know
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Old 11-18-2015
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If you have passenger side air bag make sure you unhook the battery at least 30 minutes prior to working in that area.
Air bags are powered by capacitor backup, they can store a charge for approx. 30 minutes after battery power is disconnected.
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Old 01-21-2016
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hello, I replaced my t-stat on my duratec cause my temp Gauge was pegged on cold and I had just barley warm air with max heat selected. Mine didn't have the sensor on it so it was only 28$ After I got everything put back together I refilled the pressure tank and the engine didn't want to take the antifreeze it eventually sucked some in I had to drive around with the cap loose before I could put anymore in , I finally put as much in it as I took out but the level was low when I started and the pressure tank is full right now so I'm assuming I still have some air pockets in my system ?? My gauge reads right where it should now a little under half but when I'm just idling my heat goes cold/warm when I'm on the gas it's hot. I pulled the vac hose off the valve under the hood with my heat on high and felt no vaccum I remember pulling it off before playing under the hood and felt suction. Any recommendations ?
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Old 01-21-2016
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Originally Posted by 04Duratec View Post
hello, I replaced my t-stat on my duratec cause my temp Gauge was pegged on cold and I had just barley warm air with max heat selected. Mine didn't have the sensor on it so it was only 28$ After I got everything put back together I refilled the pressure tank and the engine didn't want to take the antifreeze it eventually sucked some in I had to drive around with the cap loose before I could put anymore in , I finally put as much in it as I took out but the level was low when I started and the pressure tank is full right now so I'm assuming I still have some air pockets in my system ?? My gauge reads right where it should now a little under half but when I'm just idling my heat goes cold/warm when I'm on the gas it's hot. I pulled the vac hose off the valve under the hood with my heat on high and felt no vaccum I remember pulling it off before playing under the hood and felt suction. Any recommendations ?
Post this in a new thread so more people can see it
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Old 01-21-2016
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Quote:
Originally Posted by 04Duratec View Post
hello, I replaced my t-stat on my duratec cause my temp Gauge was pegged on cold and I had just barley warm air with max heat selected. Mine didn't have the sensor on it so it was only 28$ After I got everything put back together I refilled the pressure tank and the engine didn't want to take the antifreeze it eventually sucked some in I had to drive around with the cap loose before I could put anymore in , I finally put as much in it as I took out but the level was low when I started and the pressure tank is full right now so I'm assuming I still have some air pockets in my system ?? My gauge reads right where it should now a little under half but when I'm just idling my heat goes cold/warm when I'm on the gas it's hot. I pulled the vac hose off the valve under the hood with my heat on high and felt no vaccum I remember pulling it off before playing under the hood and felt suction. Any recommendations ?
You will only get vacuum at MAX A/C and OFF. When vacuum is applied the valve shuts the heater core off. So when you have it on heat and you don't feel vacuum this is normal.

Just draining from radiator is partial drain.
Draining from radiator and removing thermostat housing hose is full drain.

Here is the procedure for partial drain:
1. Ensure draincock is closed.
2. Fill reservoir to 15 mm above max fill level.
3. Install Cap
4. Start engine and hold at 2,500 RPMS for 8 minutes until the thermostat opens.
5. Maintain 2,500 RPMS for additional 3 minutes.
6. Increase speed to 4,000 and hold for 5 SECONDS.
7. Drop engine speed to 2,500 and hole for 3 minutes.
8. Stop and check for leaks.

For full drain:
1. Draincock closed.
2. Fill to max fill level.
3. Start engine and run for 10 seconds at 2,500 rpm to prime heater circuit then turn engine off.
4. Add coolant to 15 mm above fill line.
5. Do steps 3 through 8 in first section.
6. Repeat 4000 rpms for 5 seconds and 2,500 rpms for 3 minutes.
7. Stop and check for leaks.
8. Verifiy level after 20 minutes of cooling. Top off to max fill line.
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