Classic/Antique Car Repair: location and difficulty of replacing heater core on a 1970 cadillac deville, radiator repair shop, vacuum hoses

Question
1970 cadillac deville - 12,221 actual miles - Comfortron system works properly when set on highest temp setting or lowest temp setting - heat - any setting other than these will result in fogging of the interior windows and of course that great smell of anti-freeze.  I am assuming from past vehicles that the heater core is the culprit but am not seeing any leakage outside of or inside  the vehicle. I am anxious to fix problem before leaking starts and ruins carpet inside.  Am I overlooking some other issue that could be causing this?? Am I correct in assuming that this is a monster job if it IS the heater core??  Fluids have recently been changed (not flushed) after the cadillac had been in a 24 year coma.  Do you access the core from the inside of the car or the outside?  Thanks for your help!

Answer
You are probably right in guessing that it is the heater core, but you should check around in the area when you are removing the heater core to see if some other item is leaking when the heater is on.  It is possible for the heater control water valve or some of the connections from it to the core to leak.

The heater core comes out from the engine side, but you do have to remove the servo wiring, vacuum storage tank and master switch, plus control cables and vacuum hoses to get at it. Be sure to mark all those items so you don't have a problem getting them hooked up right again.

The air modulator assembly has to come out next, then the heater core is accessible.

If you have a good radiator repair shop in your area, they can order new core material from their supplier and re-use your old end caps and fittings to make a new core for you.

This job is not fun, and it's hard on the back, but you can do it if you take your time and have good tools and good light to work in.

It sounds like a wonderful car to drive - I had a 70 Coupe deVille for quite a while - one of the best road cars I ever owned!  Mine had 46,000 miles when I sold it.

Dick


In thinking about this later, I realized I should have added that if you are SURE there was no coolant leakage when the heat was set to maximum, the problem isn't the core itself, it must be in the heater water control valve - and it only leaks when it is partly on, not all the way on or all the way off.  Since you get to that the same way, you should check that first, maybe you won't have to have the heater re-cored.

Dick