I was driving around yesterday in my 1996 Toyota Tacoma (2.4L, 2WD, EXCAB) and the heat was working great. When I started my truck today and took off for work and the heat blew nothing but cold air at me.

Some points worth noting...

- Heat worked one day and was cold the other. The heat loss wasn't gradual, it just quit working.

- The coolant is full (the overflow is about 1/4 full when cold)

- There are no leaking fluids underneath the truck (which makes me think it probably isn't the heater core

Could anyone help me trouble shoot the problem or give me a list of things that are likely to be wrong so I can follow up on them myself. I would prefer not to take this to a mechanic if the problem isn't too severe.

 

I'm not as familiar with these newer engines as with old ones, but on older ones anyway, there's a valve which allows coolant to flow from the engine compartment in through the firewall and into your heater core, when you move the temp dial it opens and closes. That sometimes stops working.

It it hard to move the temp dial from cold to warm? Or does it move nice & smooth? Have you tried different settings? Is it cold on all of them (defrost, feet etc)?

That's all I can think of. I'd say heater core, but I don't think it would work one day and quit the other. It'd probably slowly stop putting out heat. Unless something really big somehow dislodged and clogged it. Kinda doubtful.

 

It it easy to move the heat dial from cold to warm. Cold blows no matter what setting I set it to.
I'll check up on the value you are talking about.

 

Heater control valve is what it's called. But for me, if it's stuck, I've always been able to tell because I can't move the dial back & forth.

 

Actually I lied. The heater knob won't move all the way to the left (towards cold)

 

Well it's worth checking then. With my old truck the valve was right against the firewall in the engine compartment, so with two people, you could have one move the dial back & forth while the other watched to see if the valve was opening & closing. But I feel like on these trucks it's probably up under the dash somewhere, which might make it pretty hard to get at. Not sure...

I'd definitely look into what it takes to get at that thing. Maybe there's a way to get in there and see if something is blocking it or if it's not working. Something might be binding the cable, or the valve itself might be stuck somehow. But you'd think it wouldn't move all the way to warm, not cold...

Anyway. Might not be your problem but probably worth looking into.