2020 Explorer Platinum with intermittent cabin heat

[mx270a]

I have a 2020 Ford Explorer Platinum with intermittent heat in the cabin. Sometimes it will blow hot air in the cabin while moving, but when the car is parked, no heat. Sometimes it has heat while parked, but will go cold when moving. Other times it will work for an entire trip, or not work at all for a day or two. It seems random when it will blow warm air. Sometimes it will work for 30 seconds, then cold air again.

I believe the issue is related to not circulating coolant to the heater cores. When the issue occurs, I can verify that the pipes going to the heater cores are not hot.

I have flushed the heater cores backwards and forwards. There doesn’t seem to be anything blocking the flow.

I have tested the diverter valve in the heater core circuit. The resistance on the coil looks normal at 16 ohms. There is voltage on the wire harness. With 12v DC applied directly to the coil, I can hear and feel the valve spool moving.

I suspected the issue might be the auxiliary coolant pump for the heater core circuit, but didn’t have a way to test it. So I bought another pump and plugged it in, and can verify that it does spin, so I know the wire harness is sending power. I then swapped the pumps to see if there was any debris inside the original pump to stop it from working. No change with the new pump.

This vehicle was built in June 2019, so it’s one of the early builds of the 2020 model year. Currently has 36K miles on it. Also worth mentioning is this vehicle had been in an accident by a prior owner, damage to the left front wheel, quarter panel, and driver’s door. The cabin heat has not worked normally since I’ve owned the vehicle, so it’s possible the issue is somehow related to the repair. Everything else works normally on it. I took it to a dealer last winter but of course it was working normally that day and they could not reproduce the issue.

I’m out of ideas on how to troubleshoot this issue. Where do I go from here?

 

[Rick]

Unfortunately I don't have an answer for you, but I did learn something. I had no idea there was an auxilary coolant pump. Where is it located?

 

[mx270a]

The electric aux coolant pump is located on the passenger side near the front right wheel. It's low in the engine bay. You can see it from above, but replacement is from below. Attached is a picture.

The diverter valve is on the driver's side and is accessible from above.

 

[peterk9]

Welcome to the Forum.
I thought it might be a sticking thermostat, but upon further investigation found that some modern cars now use a coolant control valve regulated by the engine computer.

Peter

 

[mx270a]

I too wondered if the engine thermostat could have any effect on this, but the coolant temperature gauge on the dash holds steady once the engine gets up to temp.

 

[MNgopher]

I too wondered if the engine thermostat could have any effect on this, but the coolant temperature gauge on the dash holds steady once the engine gets up to temp.

The engine guage is severely "dampened" electronically. Check engine temps using a scan tool to reveal what actual temps are.

My F150 (I know, not the Explorer, but I have not watched it as closely here) shows a similar guage position from 165F to 220 F as an example.

We have noted that the Explorer struggles a bit more building and keeping heat in very cold weather (like below -10F) that the one it replaced. Is that the difference between a small 4 cylinder and the V8 in the old one? Or a function of the coolant / transmission fluid heat exchanger trying to keep the transmission fluid hot? (The V8 was has a traditional cooler with a thermostat, but now way to add heat other than what the transmission created itself...)

 

[mx270a]

Last night I decided to collect some data on what the engine coolant temperature actually is. I connected a laptop with FORscan and went for a drive on the highway. Outside temperature was about 15°F. Operating temperature on my engine leveled off at 83-85°C (181-185°F). I also monitored the aux coolant pump status and the coolant bypass valve. I noticed a trend that when the bypass valve is 'OFF', I get heat in the cabin. When the bypass valve is 'ON', no heat. It is set to on most of the time.

So I went under the hood and unplugged the cable going to the bypass valve. Heat has been working great since then with several start/stop cycles, some idling, and about 30 miles of driving.

Now I'm wondering how this system is supposed to work? Is the computer controlling the bypass valve backwards, or did the bypass valve get assembled backwards?

 

[mx270a]

Issue resolved - two coolant hoses were connected incorrectly.

The coolant bypass valve is for the transmission heater/cooler. This valve is open when unpowered. Coolant is supposed to flow out a port at the top front of the engine on the passenger side, down to the valve, then back to the transmission.

As for the heater core circuit, coolant comes out of the top back of the engine, through the heater core(s), to the electric pump on the passenger side, and is then supposed to go to a hose with a T that connects to the reservoir and back to the pump inlet.

In my case, the aux pump outlet was connected to the inlet of the valve, which is powered closed most of the time in the winter. Thus the valve was blocking coolant from flowing through the heater core circuit.

Also, the purpose of the electric water pump is for engines with auto start/stop so it can keep hot coolant flowing to the heater core(s) while the engine is off at a red light.