85 heater core replacement
Drifting
Joined: Dec 2004
Posts: 1,834
Likes: 2
From: Doylestown PA
It's a BIG pita!
But take your time and you will save big bucks by doing the job your self.
You will need a 7mm swivel socket to get to those stupid bolts at the fire wall. There will not be enough room for a universal joint and the 7mm socket.
But take your time and you will save big bucks by doing the job your self.
You will need a 7mm swivel socket to get to those stupid bolts at the fire wall. There will not be enough room for a universal joint and the 7mm socket.
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
This is about the only way unless you are small, really,really small. And to repeat the often said; Gm starts with a heater core and builds the car around it.
Team Owner
Joined: Jan 2003
Posts: 20,322
Likes: 249
From: Summerland B.C. Canada
This going by my fuzzy memory 
Disconnect battery
remove seat
remove passenger foot-well panel
remove ecm
remove diagonal dash brace
remove duct work from HVAC housing
disconnect mixer door rod
remove perimeter screws from housing and wiggle it out
remove heater hoses from core
remove 2 screws holding core strap
remove core
Here are a few pics to shed some light. The top housing screws will drive you mad. I had the core re and re in an hour and a half, but spent another hour trying to install them damn screws. Less than a 3 hour job if those screws don't give you much grief.
Disconnect battery
remove seat
remove passenger foot-well panel
remove ecm
remove diagonal dash brace
remove duct work from HVAC housing
disconnect mixer door rod
remove perimeter screws from housing and wiggle it out
remove heater hoses from core
remove 2 screws holding core strap
remove core
Here are a few pics to shed some light. The top housing screws will drive you mad. I had the core re and re in an hour and a half, but spent another hour trying to install them damn screws. Less than a 3 hour job if those screws don't give you much grief.
Drifting
Joined: Dec 2004
Posts: 1,834
Likes: 2
From: Doylestown PA
remove perimeter screws from housing and wiggle it out
The top housing screws will drive you mad. I had the core re and re in an hour and a half, but spent another hour trying to install them damn screws. Less than a 3 hour job if those screws don't give you much grief.
The top housing screws will drive you mad. I had the core re and re in an hour and a half, but spent another hour trying to install them damn screws. Less than a 3 hour job if those screws don't give you much grief.
Good Luck!
Moderator Emeritus
Joined: Jun 2002
Posts: 46,133
Likes: 111
From: Maryville Tn
CI 5 thru 12 Veteran
St. Jude Donor '09 thru '23
NCM Sinkhole Donor
That's how I did my '85. It wasn't that bad (but I'm not that big). I think the original post (removing the seat to do it from underneath the dash) was posted by RonsRed88. I think you'll find his post very helpful. 
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Intermediate
Joined: May 2008
Posts: 38
Likes: 1
From: Yuba City CA
C4 heater core
I just did this. Previous message will work. If you don't mind standing on your head, this will also work. Take out the hard top so you feet have somewhere to go. Your cat will want to sit on you while you do this.
Step 1. Disconnect battery and heater hose from under hood
Step 2. Take out the passenger side panel under dash
Step 3. Remove ecm (unhook battery before you do this)
Step 4. Unbolt diagonal brace from dash and swing out of way.
Step 5. Pull or remove ducting to get out of the way.
Step 6. Remove screws from housing (feel for the top screws)
Step 7. Take out heater core strap and carefully remove old core
There is a seal around the heater core housing. This will be a pain in the neck to get back. I glued mine in with RTV to on side and let dry.
You will have to aim the core tubes through the dash. A helper makes this easy enough. I did this in under 4 hours.
Doug
Step 1. Disconnect battery and heater hose from under hood
Step 2. Take out the passenger side panel under dash
Step 3. Remove ecm (unhook battery before you do this)
Step 4. Unbolt diagonal brace from dash and swing out of way.
Step 5. Pull or remove ducting to get out of the way.
Step 6. Remove screws from housing (feel for the top screws)
Step 7. Take out heater core strap and carefully remove old core
There is a seal around the heater core housing. This will be a pain in the neck to get back. I glued mine in with RTV to on side and let dry.
You will have to aim the core tubes through the dash. A helper makes this easy enough. I did this in under 4 hours.
Doug