That number is all over the board depending on how the coolant has been maintained, whether the core is grounded or not, and the quality of the core. I'd expect 5-7 years would be on the short end; I just replaced the original heater core in mine after 21 years of service. I'd guess that's on the long end. The only other two I've got experience with - my first car was 55 Chevy and I had to change the core in it in '72 - 17 years. My wife's 67 Datsun 411 had to have a core in 74 - 7 years. Grounding them really helps longevity as galvanic corrosion is the cause of most heater core failures and a ground strap puts a stop to that.
I'm looking at changing my core as preventitive maintenence. The rest (every piece) of my cooling system will be new, so I might as well go for this, too. I'd also rather have the core replaced before it goes out, and prevent leaking coolant in my car. After reviewing the steps, I'm wondering if I should just wait until it goes out! It wouldn't be so bad, but I have extra wires running through the dash to work around, also.
Insane?? ahhh Yeah! Heater core install takes all frecking day to do and you have to completly rip your whole dash out to do it..I would wait until it goes out and since summer will be here in a few months, I would by-pass it until fall..thats what I would do..
Go for it - when they go out they usually give little warning, and getting the smell of antifreeze out of the padding and the carpet is next to impossible. Besides, putting it off til fall just means you'll be forced to do it then.
My heater core lasted 15 years, I really don't see the point in replacing it if you don't have to. If you are bored and want to take out the dash for no reason more power to you.
I helped a friend of mine change his out. It wasn't a hard job you just need to set apart the better part of a day for it. My heater core is still going , and I don't plan on touching it till I have to. I do see your point though, when mine does go out I am sure it won't be in the summer time where I can bypass it till I get a chance to fix it. It will break int he dead of winter. I have never heard of grounding it like Michael Yount suggested, but it makes perfect sense and I hope I remeber to do that when the time comes to swap mine out.