No heat at idle when warming up.

[SilvererSHO]

I'm assuming the heater core draws coolant after it goes through the turbos and that's why you get heat in only a couple of minutes on our Ecoboosts?  Over the past week I've noticed that I get heat if the engine is revving above about 1200 or so RPM but then if I'm stopped at a light it blows cold while idling.  I take off from the light and I again have warm air blowing after 2-3 seconds.  I've put it in neutral at the light and revved it up slightly and get heat too.  It only does this when the engine isn't fully warmed up and it seems like it acts normal after (I assume) the thermostat starts opening up.  Is this normal?  If so, what is causing this?  Coolant level is fine.  Could add 8-10 ounces is all.

[markssho]

I'm assuming the heater core draws coolant after it goes through the turbos and that's why you get heat in only a couple of minutes on our Ecoboosts?  Over the past week I've noticed that I get heat if the engine is revving above about 1200 or so RPM but then if I'm stopped at a light it blows cold while idling.  I take off from the light and I again have warm air blowing after 2-3 seconds.  I've put it in neutral at the light and revved it up slightly and get heat too.  It only does this when the engine isn't fully warmed up and it seems like it acts normal after (I assume) the thermostat starts opening up.  Is this normal?  If so, what is causing this?  Coolant level is fine.  Could add 8-10 ounces is all.

Lots of threads about this, common issue. Just top off the antifreeze level. Fill it slightly above the full mark.

Sent from my XT1094 using Tapatalk

[ncole]

I'm assuming the heater core draws coolant after it goes through the turbos and that's why you get heat in only a couple of minutes on our Ecoboosts?  Over the past week I've noticed that I get heat if the engine is revving above about 1200 or so RPM but then if I'm stopped at a light it blows cold while idling.  I take off from the light and I again have warm air blowing after 2-3 seconds.  I've put it in neutral at the light and revved it up slightly and get heat too.  It only does this when the engine isn't fully warmed up and it seems like it acts normal after (I assume) the thermostat starts opening up.  Is this normal?  If so, what is causing this?  Coolant level is fine.  Could add 8-10 ounces is all.

Lots of threads about this, common issue. Just top off the antifreeze level. Fill it slightly above the full mark.

Sent from my XT1094 using Tapatalk

I also don't really get good heat blowing when I remote start and let it warm up. I am wondering if an odd phenomenon  I noticed this weekend could be attributed to needing coolant added as well.  I have a 160° T-stat.  In the summer, it would run upper 170's on the interstate cruising.  Now, it runs upper 180's on the interstate.  However, I ran the car in fourth gear on the interstate and it immediately drops the coolant level to the upper 170's.  Put it  back in 6th and it goes right back up.  I assumed that is because the pump is simply turning more revolutions and able to pump fresh coolant faster to keep up, even though I am creating more heat energy.  I can't imagine the design calls for 4000 rpm in order for the coolant system to keep up.  Could this be solved by topping it off?  I did just have the coolant system flushed and filled by a Ford dealer (it was running this warm before they worked on it, and I never tried that little experiment) Or, is this a sign of some future failure in the water pump.  The dealer knowing I had the 160° T-stat of course says to replace with OEM and see, surely that's the problem.  I don't think so, but it could be?

[TSS]

I'm assuming the heater core draws coolant after it goes through the turbos and that's why you get heat in only a couple of minutes on our Ecoboosts?  Over the past week I've noticed that I get heat if the engine is revving above about 1200 or so RPM but then if I'm stopped at a light it blows cold while idling.  I take off from the light and I again have warm air blowing after 2-3 seconds.  I've put it in neutral at the light and revved it up slightly and get heat too.  It only does this when the engine isn't fully warmed up and it seems like it acts normal after (I assume) the thermostat starts opening up.  Is this normal?  If so, what is causing this?  Coolant level is fine.  Could add 8-10 ounces is all.

Lots of threads about this, common issue. Just top off the antifreeze level. Fill it slightly above the full mark.

Sent from my XT1094 using Tapatalk

You beat me to it! Yeah you would be surprised how coolant being just a little bit low can affect things like that in these cars.

[ZSHO]

Agreed! I have always added a bit of extra coolant for good measures preferably right above the TOP FILL LINE right before a cold morning startup.

Climate and Coolant mixture for reference!  Z

http://www.fortau.com/engine_coolant_check-163.html

http://www.motorcraft.com/servlet/BlobServer/engine-cooling-system-chart.pdf?
blobtable=DFYBlob&blobheader=application/pdf&blobwhere=1249081817307&blobcol=urlblob&blobkey=id

https://www.fcsdchemicalsandlubricants.com/Main/quickref/coolantsEN.pdf

[SilvererSHO]

Well adding about a pint did the trick.  Anyone know why being just a bit low causes this?  Weird....

[TopherSho]

Agreed! I have always added a bit of extra coolant for good measures preferably right above the TOP FILL LINE right before a cold morning startup.

Climate and Coolant mixture for reference!  Z

http://www.fortau.com/engine_coolant_check-163.html

http://www.motorcraft.com/servlet/BlobServer/engine-cooling-system-chart.pdf?
blobtable=DFYBlob&blobheader=application/pdf&blobwhere=1249081817307&blobcol=urlblob&blobkey=id

https://www.fcsdchemicalsandlubricants.com/Main/quickref/coolantsEN.pdf

Z is right on,  I also found that bleeding it over the span of a week also helps.

when you park it for the night or long term park it on a ramp or good incline so the bottle is elevated equal to or above the block.  Then wait about 15 minutes and pop the hood and barely crack the water cap... juuuust enough until it hisses.  then close it back up.

rinse repeat.  it will slowly dray any air in the system out over time.

[SHOdded]

Been a long time since this thread was updated, but there is a good reason to do so now

Over on shoforum, they have had situations where there is low heat at low rpm but full heat when the engine is revved.
https://shoforum.com/index.php?threads/heat-goes-down-at-red-light.140327/
Thank you to shokev for making the YT video on this topic.

Why would topping off coolant make sense?

Because ... a hose is actually leaking!  That's right, a radiator hose leak has caused the low heat issue.  May not be the case for everyone, but worth a check.