Watching this closely having the same issue on my 2014 with 145k miles. Just changes the thermostat didn’t fix the issue. Been reading it could be the blend door actuator.

 

mine did that too. check the coolant level. mine was way low. filled it and it worked again. unfortunately there is no indicator for low coolant. another brilliant feature of the explorer

 

Yeah when we swapped the thermostat we drained the coolant then filled it back up so it’s fine, been reading about it more and it could be a clogged or faulty heater core, or the blend door actuator. I have a buddy that’s a master tech that’s going to help me trouble shoot it. Will post update once we fix it.

 

Keep a close eye on coolant level. Losing coolant might be first sign of failing coolant pump. Brilliant design of your engine has an internal coolant pump. When primary seal gives out, coolant will leak out a weep hole and leave small puddle under car. Once secondary seal fails, coolant leaks into engine, mixes with oil, and destroys the engine.

 

I have been looking and I don’t see signs of it leaking. My buddy that’s a master auto tech has been helping me trouble shoot, going to try purging any air, and then if that doesn’t work try flushing the heater core and then last resort replace the pump.

thanks for replying though!

 

my leak was actually from the (2) coolant hoses behind the rear drivers side wheel! The hoses are held on with clamps that had rusted off. I replaced with stainless steel hose clamps.

 

I’d be very interested to know what you have come up with. I have 2017 Explorer 3.5 v6 and have the same issue. It only take a small increase in RPM to get all kinds of heat. I just had the water pump replaced that was leaking and it still has the heat issue

 

No coolant loss. I topped the coolant off a few weeks ago and it hasn’t dropped since, still having the issue with my heat. I think when it gets warm I’m going to flush the heater core and change the thermostat and flush the cooling system.

 

You have to follow a very specific process for filing/bleeding the cooling system, otherwise you'll have air trapped in it. It's in the service manual or you can find it on you tube.

 

I believe you just need to use a vacuum filler for cooling systems

 

Had to replace my water pump, pain in the ass but fixed the problem, took us about 8 hrs but my buddy is a certified auto tech and had all the tools needed.

 

I have the same issue with same year and engine. Water pump was leaking so it got changed. No change in the heat issue. I agree..just a very small increase in RPM gives full heat