Heat only when accelerating

[dlvommen96]

Hello everyone,

My vents blow air on all speeds and to all locations. Sitting at idle I have no hot air coming through the vents, when accelerating I get warm to hot air. Has anyone experienced this before?

Thank you in advance

2001 Ford Ranger Edge 4.0 automatic

 

[DILLARD000]

Likely a bad thermostat or air in the heater loop or a plugged core.

 

[dlvommen96]

I've been driving it around and it hasn't gotten hot. It seems like it accurately reads the temp.

 

[Uncle Gump]

So... sitting at a light it blows cold air. Take off from light it blow same amount of air but warm?

 

[dlvommen96]

Correct.

 

[RonD]

Odd one

When you are driving and warm air is coming out the vents, turn the TEMP knob to COLD to see if air gets cold, and then back to HOT to get it back to warmer air
This is operating an ELECTRIC motor on the Blend Door in the cab vent system


After warm up and idling, feel both heater hoses, both should be hot, same as upper radiator hose hot, hotter in fact

If hoses are not hot
In the engine bay is the heater core bypass valve, has 4 hoses and a Vacuum valve
Unplug the vacuum hose, engine still running
See if the hoses start to get hotter
Bypass valve should have no vacuum present unless MAX AC is selected

 

[rubydist]

The heater system is a partial bypass of the cooling system as provided by the water pump. When you mash on the gas, the engine is running significantly faster, therefore the water pump is moving more coolant through the system - therefore more coolant is flowing through the heater core. So, that suggests that you have one or more of the following problems: water pump vanes are worn, hoses/lines to heater core are partly plugged up, heater core is partly plugged up. I had a F150 a few years ago with pretty much this problem, the lines to the heater core were nearly plugged, so not enough coolant was circulating to the heater core.

 

[dlvommen96]

Thank you guys. I'll check the vacuum lines tomorrow. Do you guys have any tips on flushing the heater core? I've seen it done with a pressure washer, is that the only way to do it?

 

[Eddo Rogue]

I flushed mine with a regular hose. Then spliced in a bleeder valve tube I got from fleabay. I had a temp gauge fluctuation issue, which did get solved.

 

[RonD]

Heater hoses at the firewall should be reversed every 2 years or so, this back flushes the heater core while driving, helping it last longer

Once heater core is partially blocked, it will just get worse over time
Coolant has anti-corrosive chemicals that continuously coat the metal parts of cooling system as it circulates
If a passage in heater core(or radiator) gets blocked then no circulation and no anti-corrosive protection, so corrosion gets worse and blockage gets worse

CLR or Vinegar can help clean up this corrosion.................in some cases, but it has to get to the corrosion, lol
You can remove the heater hoses AT the BYPASS VALVE
Point 1 hose down and BLOW into the other hose to try and get as much coolant out as you can
Use CLR or vinegar mixed with hot water, the hotter the better
Pour it into the heater core
Let it sit for 20min and then flush it out with garden hose
REPEAT

Then REVERSE it, point other hose down at the ground and fill with CLR/hot water from the other direction
And flush, REPEAT

Do it until nothing foreign seems to be coming out when flushing, your call


I would not use air compressor or pressure sprayer, this system is designed to hold 16psi pressure, so you WILL blow off parts if you use HIGH pressure, especially if there is corrosion in the heater core that has weakened the metal tubes
You will end up with a coolant leak into the cab from the heater core, if a tube breaks from the HIGH pressure

 

[dlvommen96]

Hello everyone,

I flushed the heater core with a garden hose, I have to say, the heater core really did not show any pressure or resistance, everything flushed out fine and smoothly. Still having the same problem. I checked the vacuum lines and didn't see or feel anything wrong.

I think the next step I should take is replace the vacuum lines and double check the radiator hoses.

Is it possible to have some type of clog in the radiator? If so do I just try to flush it the same way I did the heater core?

 

[RonD]

Clogged heater core can flow just fine, but its only flowing thru top of the core so lower core has no flow so no heat

After engine warm up and at idle, and have blower/fan off
Feel the 4 heater hoses at the bypass

Hot coolant comes from the lower intake, by thermostat housing, on one hose to the bypass, should be the hottest hose of the 4 on the bypass
If the bypass is "open" that hot coolant flows thru and TO the heater core, so those 2 hoses should be the same temp, hot, if not then bypass is diverting some of the flow

The other hose on the firewall is the return hose, it runs to the bypass, it should be hot as well if blower/fan is off
4th hose on bypass runs to the water pump, it recirculates the coolant that just passed thru the heater core
It should also be hot since no heat was being pulled out by the fan blowing air thru the heater core

If the bypass valve is failing then hoses to firewall will be cooler, hot coolant is being diverted back to water pump
As RPMs increase enough hot coolant is making it to heater to get some heat

 

[DILLARD000]

Which HeaterValve is on this 2001 4.0L: 4wayHeaterValve or 2wayHeaterValve?
2way is usually factory mounted under Alternator in HeaterCore return line to Pump.

 

[dlvommen96]

Which HeaterValve is on this 2001 4.0L: 4wayHeaterValve or 2wayHeaterValve?
2way is usually factory mounted under Alternator in HeaterCore return line to Pump.

View attachment 72942

I have the bottom one

 

[dlvommen96]

The two way