Heater Core - To bypass, or not to bypass, that is thy question


Founding Member
Dec 2, 2000
Lehigh Acres Fla.
As some of you may or may not remember, I had to replace my radiator. Car sitting for years and running it off and on just wasn't enough. All that slimey rust colored coolant killed the radiator. So now I have my new FRPP 2 core radiator. I flushed the system before I tossed the old rad out. I even scrubbed the overflow tank out good. It has been sitting for a couple months now. My question, should I bypass the heater core before I connect my new radiator? It wasn't leaking the last time I checked. But if I put my new rad in, I'm afraid garbage inside the heater core will come out and contaminate my new cooling investment. I'm not sure what I should do. How many of you southerners have done this?

One other thing.. I replaced all the coolant hoses on the front except for the upper which looks like new. I never had to remove the water neck or T-stat, but from what I remember, the ass end of the water neck where the upper hose goes in was nasty loaded with that rusty slime. I had to scrub that out. Is the T-stat going to be alright here? Is it worth trying to remove the water neck just to clean the gunk out? Dont want it getting stuck later. No leaks there the last time I ran it. But I know how those bolts get seized in there and snap. Heck, I can't even figure out what size the bolts are. 13mm is way too big with lots of slop. 12mm appears to not fit.. 1/2" fits but still has a bit of slop. That right bolt is a pain. They put every friggin thing in the way.

Suggestions... tips... ideas.. 2 cents.. welcome to everything right now. Thanks everyone in advance.
  • Sponsors (?)

Disconnect the heater core, go to autozone and buy a 6 foot lenght of heater core hose. Connect one end and point it down to ground and then take other end and connect garden hose to core and flush.....
Id just swap the heater core. Its probabbly already rusty and corroded. Its not as bad as everyone thinks to swap it either. I can have it out and in under 2 hours.
Id just swap the heater core. Its probabbly already rusty and corroded. Its not as bad as everyone thinks to swap it either. I can have it out and in under 2 hours.

You gotta be kiddin me! I'd rather tear an engine apart , remove the transmission and swap gears.... rather than attempt doing a heater core. I'm better off bypassing it if it's that bad. This isn't my DD, if it gets cold.. I'll just drive my DD if I need heat that bad. I've seen a couple dozen heater core jobs when I worked at the Ford dealer... Thats is NO cake job. 10 hours on average for heater core replacement.. not to mention sliced up hands .. pinched fingers and a LOT of headache. Not worth it IMO.
After having my Heater Core replaced twice I just bypassed it when it went again. Live in Central Florida so no worries for heat that often (except this year). But my Stang isn't my daily driver. Heater Core was bypassed years ago, no problems. '93 Coupe.

The way I see it, I'm better off bypassing it. Not worth the risk to my radiator to flush and re-use the original, and I'm not about to tear the dash out. I have never done that so I dont have a clue what I'm doing. Maybe some other time, perhaps. But not now. I want to get this thing done so I can drive it for a change, instead of sittin in my driveway eroding. If you wanna come down and do it, you're welcome to. Otherwise, I'm not touchin it.

Appreciate the feedback, as always, it is welcomed.