89 MGM No Heat Problems

I have a 1989 Grand Marquis. We have replaced the Thermostat, water pump, and radiator cap so far. We have flushed the entire system also. Before the system flush, one side of heater core was hot, and the other luke warm, now both are hot. BUT, still having heater problems! Sometimes I have luke warm heat, but most of the time, cold heat. We have tried putting something in front of the radiator... still no change. I was told that the inner core temp was only running 140 degrees. When car sits and idles for 20 minutes or so, heat is better, but as soon as you start to drive it, cold! Any other ideas for me to try??? I really like this car... rides great, and looks good! But living here in Iowa.... heat is a must! HELP ME PLEASE! Thanks

I had a similar problem a long time ago. Believe it or not it was caused by too much anti-freeze. We put straight anti-freeze in it and it cooled so good we couldn't get any heat out of it. I put a temp gage in the dash and it would only come up to temp after idling for quite a while. As soon as you started moving the temp dropped about 70 degrees. We finally drained the anti-freeze and put in a 50/50 mix. Problem solved.

Thanks for the idea.... but, already have only 50/50 in it! thanks again!