No heat

[Treleaven]

My cousin has a 1994 Mazda B4000 with a 4.0L which should be the same as a 1994 Ford Ranger, and similar to the 1994 Ford Explorer I am assuming so that is why I am posting here. Because I know you guys know this issue because I had to address it on my 1997 Explorer.

Anyways, he has no heat in his cab. I changed this thermostat, and I changed the temp sender to the gauge which fixed his engine feeling overly hot and his transmission to switch gears properly.

We have looked high and low on the internet for answers but I cannot figure out what the problem is. His heat will sporadically come on and work perfectly but most times it is just blowing cold air. The hoses leading into the cab are both cold at all times unless the heat is working in the cab and then they get hot. To me, it would seem that something is clogged in the hose, but if it comes on now and then (once ever 4 days for 10 minutes) would it not be getting unclogged?

We are in serious need of your help as snow is a week away.

 

[Kevin Barry]

Have you checked to see if the blend door is stuck?

 

[Treleaven]

We ruled out the blend door as the heat sometimes works while it is set to heat all of the time so no settings get changed and it will crank hot air.

Also, the feed and return hoses leading into the cab are both cold leading me to presume that the heat isn't even getting to the cab.

Thank you for the suggestion though and please correct me if my presumptions are wrong.

 

[Kevin Barry]

I am most familiar with second generation Explorer's but here is where I would look:

1) Make sure the blend door is operating. Simply listen behind the glove box as you dial the switch between settings (i.e. floor, face, defrost, etc.)

2) Ensure the rotary switch is in fact properly connected that regulates the temperature.

3) Based on two cool hoses in/out it may be the heater core itself is clogged. What was/is the condition of the coolant when you removed the thermostat? Has your friend ever smelled a sweet smell in the cab when the heat was on?

4) Air bubble in the lines. But should burp itself out after driving.

 

[huntman58]

On the 94's there is a shut off vacuum valve in line on the heater hoses before they go into the fire wall. It is run from a vacuum switch on the temp controller inside the truck. It runs to the pass side and then comes threw the fire wall to the valve. this same vacuum line also runs the air door for recycled air or fresh air from out side and if you open and lower the glove box you can see it and check to see if it is also working ( moves down to cut off out side air and up to let in fresh air) .

How to check if it is the valve
Make sure the hoses are hot before the valve if they are then great.
Now see if they are after the valve.
If not the problem is the valve is not working.

How to fix if found not working
Two ways to take care of this one.
Trouble shoot it to see if it’s getting vacuum and opening the valve. If the valve is opening then there is an obstruction in the valve and it will have to be replaced. If no vacuum then trace it back tell you find the reason why and correct it.

The other option is to convert it like the 93 and earlier explorers. run the hoses right to the heater core with out the valve ( do not forget to block off the vacuum line so that you do not have a vacuum leak. You can plug it with a screw or bolt).
doing this will make the AC work a bit harder in the summer as hot water will flow threw it all the time.

That is the most likely reason for no heat in this case as you explained it and the two ways to fix it

 

[Treleaven]

Perfect, we will definitely check that out today to see if that will help us out. He did just have a bunch of young lads in a mechanics class in high school change the head gaskets before he bought it so maybe something happened there.

 

[Treleaven]

Update...we looked under the hood today and found no valve of any sort on the heater hoses running from the firewall to the engine.

But what we did find is that the heat started to work briefly, and that the feeder hose was getting very hot and the return hose was not hot at all.

Any ideas now?

 

[waskly]

is this a 3.0?

 

[Treleaven]

I can't believe I did not include the engine size... it is in fact a 4.0L

 

[waskly]

from the prior post sounds like the heater core is clogged, take both hoses off and run a hose through it, flush it...

also one the hoses should have a valve on it, coming from the water pump to the heater box. the inlet tho has the valve.

right side, more towards the front somewhere by cyl #1/2

 

[Treleaven]

I know you basically just gave me the best directions, but is there any chance you have a picture of it, or with the area circled? Also, would a clogged heater core still produce heat for several minutes now and then?

 

[huntman58]

A 94 should have the valve by the fire wall and the two pipes were the hoses connect to the heater core unless some one removed it already.

if that is the case as said the heater core is most likely blocked.

I just replaced mine with one from O'Reilly Auto Parts for a whole $23.00.

easy to pull also as all you have to do is take the two hoses off then in side remove the carpet formed cover under the glove box then remove 4 screws (two on each side ) that lets you take off the bottom cover then pull down and out the heater core. Install is reveres of removal.

One hint lay a towel down to soak up any spilled coolant as you remove it. With it out you can flush it good with water or compressed air or just replace it like I did.

 

[Treleaven]

Another question to add to the topic for you guys. The temperature gauge is not working on the truck. We replaced the temperature gauge sensor and it works but we believe that the wire that connects to the sensor is corroded. Can that wire be easily replaced or should we just pinch it on nice and tight after sand papering the **** out of it?

 

[huntman58]

Another question to add to the topic for you guys. The temperature gauge is not working on the truck. We replaced the temperature gauge sensor and it works but we believe that the wire that connects to the sensor is corroded. Can that wire be easily replaced or should we just pinch it on nice and tight after sand papering the **** out of it?

ground that wire if the gauge peg to the hot side its working if not it is the wire or the gauge you could trace it and find out if there is a break in it if your not getting any thing from it or I should say it will not peg the gauge or run a jumper from ground to the gauge wire close to the dash and see if it pegs it if it dose then chase that wire or run a new one in its place. another easy trick is called after market temp gauge and an a pillar pod gauge holder and with it you can add say a trany tem gauge if you have an auto or a real oil pressure gauge or even both.

By the way yes a heater core can give heat some times only if the plug is lose and moves around stopping it up here and there then working free for a bit .