Heating question

I start my 91 early to let it get to temp, get all the fluids circulated properly and heat up the inside as well. This is where the question comes in. My temp gauge will read 210 and I will not be blowing hot or warm air while i am parked. As soon as i get in and start driving, the air becomes warm/hot. Any deas on why this is occurring? I noticed it the last week or two when I decided to let it warm up before going anywhere.
Thanks in advance for ideas.

heater control valve may not be opening(vacuum) until the rpm's are increased.

why warm it up so long? it really is a waste of gas.

Heater control valve actually operated opens when there is a lack of vacuum.

However I was running an AutoZone thermostat. Although running just slightly under 210, I was barely getting any heat at all.

I've had great luck with Stant and OEM Dealership thermostats.

Worth a try, easy to replace.

89xj said:

heater control valve may not be opening(vacuum) until the rpm's are increased.

why warm it up so long? it really is a waste of gas.

Click to expand...

A couple reasons for the warmup- I have an engine knock i do not wish to exacerbate, I have a 3 year old I take to school in the AM, and it was zero degrees. At work I do not have a lengthy ritual, but this usually only takes me five minutes or so.

I replaced the HCV when I replaced the hose leading into it the plastic broke and left me no choice. I scoured the bone yard and could not fine ANY that were the same as mine, it is all plastic, so I had to go to JEEP and make sure I had the correct one.

Sounds like the vacuum line broke or popped off of the vacuum cannister behind the passengers side front bumper. You aren't getting enough vacuum to the heater pots at idle to open them.
The small black vacuum line from the vacuum reservoir to/through the firewall, supplies the vacuum for the flap pots and the vacuum for the water valve (through the heater controls).
If it isn't the main vacuum line or a cracked vacuum reservoir, it may be the vacuum plug on top of the HVAC controls, I've popped it loose messing with the radio and wiring before.
The main vacuum line (3/8" or so thick) from the intake across the firewall, atop the passengers side wheel well, under the battery tray to the reservoir behind the bumper, has a tendency to rot under the battery tray from acid spew. Or it can just get old and crack.

My $ is on a plugged heater core. It is possible to backflush it, and that's how I saved myself a heater core job actually.

I'll check the easy option first and check vacuum lines as it is below freezing still. Thanks for the ideas!

The heater core valve is open when there is no vacuum applied to it.

make sure you dont have any air pockets in the cooling sys