I got such a good response on my motor mounts i thought i would throw this one out to everyone. I keep blowing the heater core. I need heat (just to defrost the windows) so i would like to keep it. Any thoughts. Thanks for the help.
What temp is your engine running at? Also, I would make sure to flush out the whole cooling system as an ubstruction could cause extra stress on the core. Maybe you could try putting a restricter somewhere in your heater lines and see what happens. I remember having a heater core blow from just changing out a crusty radiator to a new high flowing one. It was neat, there was green steam shooting out of the defrosters and filling the whole driver compartment up. Not fun.
If you are replacing heater cores that often make sure you go to the Kragen, Pep Boys or whatever the big chain auto store is and get the lifetime warranty. This way you can save money while you investigate the problem.
I'd make sure the pressures in the cooling system are ok (squeeze the cooling hose as it goes into the radiator at operating temp), but I think this would not likely cause metal to fatigue repeatedly, maybe one core can have a weak spot but not 2 or 3. My best guess is that the heater core is not installed properly. Make sure that when it's in it can not vibrate, shake, have a loose part hit against it, or be tweaked in any way. You can get that sticky 3/8" thick and 1/2" wide roles of rubber tape to help support it. Make sure nothing is rubbing on it as it passes through the firewall.
If it is a huge problem you could just bypass it. If you need defrost you can just cut a potato in half in rub in on the inside windows, that will prevent it from fogging up for a few hours.
the temp is running between 210 and 220 I had the radiator flushed the first 2 times and as far as i could tell it was in securly with no vibration. i had the entire system flush one time. I will either try getting a new radiator or a restrictor or both. Thanks for the help.