Mysterious heater issue with 1998 Tacoma

Hi guys. I've got a 1998 Tacoma with a poorly functioning heater. It puts out about 135 degree air from the bottom vents, cooler air from the others. In cold weather, it's not adequate. I'm out of options and ideas. Can anyone offer advice?

1) I've flushed the heater core: it seemed fine.

2) The heater valve mounted to the firewall is new, and is open.

3) I've replaced the thermostat, which did seem to improve things (before that, the air temp was slightly cooler than the 135 F. air described above).

4) The engine temp always runs slightly below the middle point of the normal range on the gauge. I've checked the coolant temp with the engine running and its about 190 F.

5) The engine warms up in what seems a normal span of time, does not appear to run cold nor overheat (so the water pump appears to be okay).

6) Coolant is in good condition, level is fine, and seems to be circulating. I don't think air in the system is a problem.

Any ideas? Is it simply that this particular year of Tacoma has an inadequate heater design?

Thanks for any help/info you may be able to offer!

 

Sounds like an air-control flap is not working. You may have to take the dash apart to visually see what is not working.
When you turn the air-control dial (on the right), do you feel (and hear) some resistance indicating that the cables and 'flappers' are moving as they should?

 

^^
I think that your water-related checks all check out okay, so it must be an air-related problem.

 

Agreed on flap door being not open all the way.

 

Rick and others,

Thank you for your information. The outside air door does operate, I've checked that. When I'm running the heat, I leave it closed and use the re-circulate position, which helps increase the air temp. Also, the fan and blower wheel operate well. I pulled the fan and cleaned the blower wheel.

Perhaps you're onto something with the temp. control knob and some other door in the system that is malfunctioning.

The temp. control knob on the dash is broken. I've disconnected the cable to the heat/coolant valve mounted on the firewall, so I simply manually keep the valve open for heating. Does the heat control selector on the dash also operate another door in the air system that is perhaps positioned wrong? The airflow seems to be fairly strong, but the cab is not getting enough heat. Also, the temp. control knob is positioned about half way between heat and cool. But, as I said, the heat/coolant valve on the firewall is completely in the open position.

Thanks again everyone!

 

Maybe this is the problem. So, this temp. control knob also operates some kind of internal flap/door in the air system? The knob on my Tacoma, as it happens, is broken and stuck at the halfway point, although the heat/coolant valve on the firewall is in the full open position with the cable disconnected.

 

Well . . . you guys were on the right track. I had no idea that the temp. control knob also moved an interior air door. I went out to the truck, and pushed the cable at the firewall associated with the temp. control knob all the way in, and, presto! Lots of hot air now!

Thanks everyone!

Next, I'll have to replace the temp. control knob. Surely the center section of the dash comes out, without having to pull the whole dash?