Heater Temp Swings

This is a weird one. I have a 1988 Buick LeSabre. It has a new radiator. 146,000 miles. Coolant is full and ok. When sitting still I have more than ample heat from the heater. However the moment I start moving it starts blowing cold air. Given the temperatures right now here in the northeast I sure would like to get this fixed fast. Anyone have any ideas as to where to start looking?

Thermostat stuck open?

OK, I'll start with that and let you know.

I'd also check to make sure all the air was bled out of the system.

Hey j09ln03,

Did you ever get your heater working ? Mine does the same thing...hot passenger, COLD driver [in all positions...heat, defrost, vent...]. It's fine when idling, the car heats up, but as soon as you dirve, COLD on driver's side!

rsvp asap!

My 90 Lesabre does the same exact thing. Its warm when sitting, but gets cool when moving. An Auto Tech told me its how the thin radiator is right infront of the vents and as soon as cold air goes thru it, it becomes alot colder. I keep it on defrost as someone told me, and i get little heat, just enough to keep the cabin warm and untill I find a better solution, thats great enough for me

Hey Buicks=OldGuyCar.
Try checking vacuum lines to the firewall to see if they are cracked or loose.
As for SarcasticE's post, I have a 90 LeSabre custom and my thermostat stuck open twice (don't use one of those failsafe things, they're the ones that stuck open!!!)I put a regular 190 thermostat in and it's perfect.
As for the thin rad core theory...I don't think so.Mine gives me lots of heat at minus 30c.