No Heat and no flow to the heater core

[MtrJunkie]

Hi all,

I'm new to explorer forums. I've only been wrenching on cars for about a year and a half...so I've got a lot to learn, but loving it!

I have a '99 Explorer Eddie Bauer 4.0 SOHC that I was given. Previous owner blew a headgasket and hydro-locked it. Since I got it, I have a rebuilt engine put in, and have done a few other things to get it road worthy (fuel pump, new IAC, Ball joints, etc.)

My question is around the heater. Its still warm enough here in TX but I thought I would test everything and I notice the air is not heating up.

To diagnose I pulled the upper and lower heater hoses and tested flow thru the core. It is ok. Then I started up the motor and noticed that there is almost no flow going to the core...what little flow there is, is coming from the port that is supposed to be the outbound from the heater core...but it is merely a trickle.

Replacing the WP was my next thought, but I am wondering, is coolant supposed to flow to the heater core always, or is there a valve that restricts it?

Oh, and last, there is currently no thermostat. I took it out over the weekend because it was bad. Will replace but would like to diagnose only one thing at a time.

Thanks in advance for any help. And I'm excited about being here.

 

[Turdle]

Yes there is a heater core bypass valve right in line on the inlet side of the heater core. It should have a small grey vacuum line on it.

It could also be an air bubble in the coolant system. try raising the front of the vehicle so the rad cap is higher than the heater core, and burp the system several times.

A "full" cooling system will spill out when the rad cap is opened, on a level surface.

 

[MtrJunkie]

Thanks, Turdle,

I put the front on ramps and "burped it". That may have helped. I tested it under load (@ 2500rpm) and the heater reached 135 F while RPMs were up. As soon as I let off, it starts a quick drop back to 85 (it's 70F outside right now). So if that is normal, then we are good...but it is obvious I am getting no real flow to the HC under idle speeds. Perhaps the heater bypass vacuum has a leak?

I think another problem is that either something is wrong with the climate control panel, or I am unfamiliar with the operation. while set on "Automatic" and temperature raised to "90", the A/C compressor actually kicks in. I would expect "Automatic" to either heat or cool, depending on the temp setting you choose. The heater only works on "Floor".

 

[nativetennessean]

When mine did that

For another reason, I unhooked the battery cables to clean them and when I finished and hooked them back up I suddenly had heat again. Worked for me.