I have coolant leaking out of the floor heating ducts of the '90 765T, so it's time to perform deep-in-the-dash surgery and change the heater core. My Volvo tech asked if i had a Sawzall for the job!! Seriously, he said it's easier to cut into the air plenum box and extricate the core than do the extra dissasembly. He said to seal the "incision" up with duct tape and you're good to go. Any insight by fellow bricksters on completing this job is much appreciated. I've read the FAQ for the job. thanks.
chris in vermont

Update: I'm about six hours into this tear down, trying to extricate the heater core. This '90 765T has an later style console-dash than other 700s, so I'm navigating through the ducts and plugs Magellan style. I found the airbag wire coupling and disconnected that. Parts and fasteners are marked and lined up in sequence of removal. Now i'm down to the air diverter box, with flaps, that conceals the nefarious and failed heater core. I've removed 7 of 8 bolts that secure this plastic box. The final way is WAY up there, hard to reach. Hopefully the full dash does not have to be removed to access that. I can pry the box open and see the core. I have the quarry in view. Tonight: more contortions and expletives. Thanks for the advice so far.
chris in vermont
244,765,r100rs, r80rt, etc.

Please post your experiences with disassembling the dash up to this point. I, for one, will need to do this job soon (once I find a replacement dash)

FWIW, I just grabbbed a decent looking heater box today at the junkyard from an '89 740. Thre were way more than 7-8 screws holding that diverter box together. More like 10-12. Keep looking for some on the right side where the wireing harness runs. I found two holding clips screwed in for the cable, plus. there are a ouple tucked up in the corner. I used feel more than sight to locate each one. Feel along the edges of the box and you'll get them all.

Once inside, you'll have four more screws. These hold a metal band on ecah side of the core. The bolts are top and bottom of these bands and deeply recessed. Iused a 7mm socket on a driver extension to do everything. Again patience and feel is needed to lock onto these four screw heads.

Once these bands are off, the heater core will come loose. Now undo the two heater hoses from the in-out pipes at the firewall and the core will slide out, with a slight pull to the right.

BTW, the bottom pipe had the hose running to the engine block, while the upper pipe had the hose running through the heat control valve. (In case you get disoriented) I doubt it matters to the heater core which way the coolant flows.
--
"Can't understand why people abort Volvos, either"

Night Two of Life Under the Dashboard of the '90 765T. In our last report, I had burrowed in as far as the diverter box which holds the failed heater core. All 7mm screws, except one near-impossible to reach at top of box, were removed. It was 2 am. i went to bed. Night Two: Once the instrument cluster was removed, and the defrost splitter tubing, there was better access to that impossible nut, way on top of the diverter box. That nut came off and I pried open the box, revealing the heater core. Working space is so tight, the diverter box and defrost splitter were pushed aside only, could not be removed, making just enough room to access the heater core. The core is retained on each end by a thin metal strap, vertical, with 7 mm screws top and bottom. I removed only the lower strap screws and could then remove the heater core. I was about 10 hours into the job at this point. I'm a novice.

I pressure tested the failed core. It spewed water from the lower right end cap, far away from the inlet-outlet nipples. As recommended, the new core was pressure tested prior to installation and it held fine. Getting the nipples through the rubber gasket at the firewall was tricky. More "Braille" work, like most of this job, part by sight, the rest by feel. The ideal worker here has long arms and small hands. I lubed the nipples with silicone grease and finally had an assistant sight the nipples from the engine compartment so i could line up the core to penetrate the firewall rubber gasket. A good shove had the nipples through the firewall. Onward to reassembly. Reapplied core retaining straps, then put diverter box back in. The footwell distribution box, under the diverter, was a real bear to force back into place. It took a pry bar and rubber mallet to persuade it home. It's midnight and i turned in. Tonight, complete reassembly, the hard work is done.

Lessons learned so far: Have a good assortment of handtools, particularly 1/4-inch sockets, various extensions and a universal knuckle attachment. Most nuts are 7mm, a few 8 mm and 10mm. Have TORX fittings handy, a putty knife to persuade stubborn ducts at junctions. I had no real instructions, so you study how parts are inconnected to minimize removal of extraneous parts. Still, I removed some panels unneccesarily. The dashboard and center radio panel remained in place, the relay panel was loosened for more working space. Have plenty of good lighting, a few stationary clamp lights, and then a flashlight or two. You're working in dark and confined quarters. Finally, keep a notebook to record step-by-step removal. I have ziplock baggies handy so all fasteners are bagged, marked and then taped to their panel. It's easy to take apart, harder to reassemble and make order of it all. FCP Groton is great, paid $110 for replacement core, ordered on Wednesday, delivered by UPS Thursday.
chris in vermont 244, 765T (in the operating room)

my problem was that I broke my evaporator connector. I did what the tech said to do for the heater core. Cut it out with a dremel diamond tip, then after replacing, applied RTV silicone around edges. It worked okay for the evap. Should work okay for the heater core!
jc

P.s. it would be helpful to go to junkyard and see what you have to do first!

Where exactly did you cut to remove the heater core?


I took out a core today at the junkyard where someone had already done the dirty work of removing the dash and ductwork, leaving me just the diverter box to unbolt to uncover the core.

It looked to me one still has to go through all the hard labor just to get into this diverter box area anyhow. So, what's the advantage of cutting when it's just a dozen more screws to remove?
--
"Can't understand why people abort Volvos, either"

Just curious: how often did you change your coolant? What do you think precipitated the heater core leak?

Steve,

I am guessing from your question that you are asking this due to your reliance on "that red stuff" -- DexCool coolant.

FWIW, I just did a coolant change on my '89 740tic, 119,000 miles, dirty green coolant, local radistor shop metal radiator, and knwn leaky heater box.

Discovered today, about 1K miles after the change over to DexCool (through flush) the radiator is leaking.

Didn't you say you had troubles with one radiator in the past?
What do you think caused that failure? Is there some incompatability with DexCool and the type of solder joints?
--
"Can't understand why people abort Volvos, either"

I have used Dexcool for ten years or so in about eight cars with zero problems, with one exception. I put a new Nissens all-metal brass/solder radiator in my 90 745 and replaced the Dexcool. Within a year, the radiator started leaking at some joints. I concluded that the Dexcool was not good for solder (and this was a lead solder radiator.) Others have noted that if you have an incipient leak, the Dexcool will find it and start leaking through it due to its lack of silicates. The latter in green coolants tend to precipitate out at leaks and plug them until they enlarge.

I have never experienced a heater core leak, probably because I change coolants regularly. The 90 745, at thirteen years old, is my test bed.

So, if I take this all metal rad to a shop and have him *brass* or *bronze* weld it to stop the small leak, I'd be on the right track?
--
"Can't understand why people abort Volvos, either"

This turbo wagon has 158K miles, with 38 k under my ownership. Coolant is green and did have a recent flush, unexpectedly, due to a heater valve failure. The heater core failed shortly after that, fortunately in summer when we don't need much heat in the north country. Wonder if the two events are connected? The car had 120K in Florida, so probably saw much hot service.

Eric from MN said watch out around the airbag. i've never messed with an airbag loaded dash/steering wheel and don't want any BIG surprises. Can anyone offer details on this point, particularly what to avoid? thanks.
chris in vermont 244, 765, r100rs, r80rt, etc.

To disable the airbag, just disconnect the battery ground cable and wait a few minutes for the capacitative charge to dissipate.

Ah the memories....uh nightmares. I did it the "hard" way, by taking apart the dash. I didn't really feel like cutting into my girl. Things I learned along the way:

1. If you don't label the screw, fastener, or other part, you'll forget where it goes.

1a. If you forget where it goes, just keep going, it will become obvious somewhere along the way. Once it becomes obvious, you will have to backtrack at least 2 steps to install it.

2. The green Volvo manuals are invaluable. The one that I thought was the correct one wasn't available anymore, so I bought the Canadian one. It was in French, but the pictures were very helpful. (So was the couple of semesters of French I took in college.) I found out later that the one I needed in English I had. It was labelled Body Fittings, Exterior or something like that. If you want/need it I can get you the book numbers. They are worth the money.

3. While you have the coolant drained, its a good change of pace to inspect/replace hoses, heater valves, radiators, etc.

4. Be gentle/careful/walkoneggshells around the airbag. (I didn't learn from personal experience; I didn't want to either.)

5. Pulling the distribution vent from under the climate control unit was the most annoying thing. I found that I needed to pull the foam rubber piece protecting the distribution vent from the tranny tunnel first. You'll understand when you get to it.

I know that there are other things to mention that I have (mercifully) forgotten about. Drop me a line if you have specific questions, or during the process get hung up on something.

Good luck!
-Eric
Vlad - '89 765t 175k - down for turbo work.
'72 BMW R75/5 - Alternate transportation