no heat

My 2002 Taurus is having heat issues. If I do city driving the engine will eventually come up to operating temp. However, if after it comes up to temp, I hop on the highway, the temp goes down almost to the point of not registering. Also, if I get on the highway right away, the engine does not come up to operating temp. I do get some warm air out of the vents but nothing compared to what it used to be. I tried a new thermostat. I also had it checked for leaks. I was told that I had good pressure in the system, and that there was no leaks. This all happened out of the blue.
Any ideas?

You should check for air trapped in the system and make sure the vacuum system for the HVAC system is good. I'm assuming you have the manual Heat/Vent/AC controls rather than the electronic automatic climate control.

Others have also experienced similar issues caused by broken impellers on the water pump. If you don't find any air in the cooling system and the vacuum system seems good, you may consider pulling the water pump and checking the condition of the impeller.

-Rod

HI David,
I work part time for a mechanic while I have no formal training myself. Yesterday we were addressing the same exact problem on a '99 Sable. My mechanic said he'd had a '97 in over the past year also with teh smae issue, and instructed me to first do a cutout of one of the pipes/hoses to the heater core to alleviate airpockets as shorod said. My mechanic said he'd called Four Seasons and they said this was the proper thing to do for that. It also apparently did the trick for the '97. Anyhow, it's just a matter of taking out the roughly 6 inch rubber hose that runs horizontally against the firewall. You'll see it's the piece in the "y" pipe. I then capped off each end fitting with a rubber cap sold in the "HELP" section at O'Reillys. Used a hose clamp as well for each.

Anyhow, this wasnt the trick really for us, as we found that the real issue is that both fans are coming on and staying on. In the Haynes manual it says to address both/either the coolant temp sensor(grey not orange) and/or fan relays. These can be found in the fuse box on top of the radiator. The owners manual shows it to be #23, a fatter relay about an inch sqaure. There's exactly 3 of this type there, and we also replaced the one to the far right....so after replacing these 2 and the CTS we still have continuously running fans. Hmm? So were both just scratching our heads. So Im here searching the forum for a final conclusion. More later.