How to mod a Heatercore (Dual 120mm version)

This is the updated version with a little tweakage to the process...the original was done last year and things have been added and changed as needed.

For some time, I have been using 1971 Caprice heatercores when I wanted to use 2-4 120mm fans for some serious cooling power. The problems with that core (barbed fittings that are a royal pain to get out and odd shaped holes punched into the top tank) led me to search for a different core.

After scanning through tons of heatercore specs, I decided to give the heatercore for the 1977 Pontiac Bonneville (with a/c) a test run if the price was right. A quick call to autozone confirmed that it was a heatercore that they normally stock and with a great pricetag of $17.99 this one looked like a sure bet for replacing my caprice cores for future mods. (Note: AutoZone has since had an unusually high number of the b'ville cores with brass tanks instead of the copper ones - check all of your local auto stores for the best price and make them pull it out of the box before you buy it - the copper ones have a color much like that of a new penny - I will add pics and a better description of how to tell them apart a little later)

Quick run down of the specs:
10-3/4" X 5-5/8" X 2" w/o the tanks
about 12-1/2" X 5-5/8 X 2" with the tanks

To put the size into perspective, this is the '77 Bonneville core with two 120mm fans laying on top of it:

Almost perfect...

On to other good points of this core:
One of the best things about this core are the holes in the tanks for the fittings. They are not odd-shaped oval disasters like the ones that are punched into some cores. Instead, they are almost perfectly round and their size makes the switch over to barbed fittings much easier than you would expect.

Pic of the top tank with the factory tubes:

^nice round holes -- that are the same size.

As I mentioned earlier, the caprice cores that I had been using started causing problems as the tubes were barbed -- they are almost locked into the tanks and it is very hard to get them out without cutting, drilling and some torch work -- when they are gone, they leave nasty oval punchouts that are a PITA to seal up properly. Due to the barbs on the factory tubes, if you try to heat them up and yank them straight out, it will tear the brass on the tanks - another headache. I halfway expected the tubes on the '77 Bonneville to be barbed like those on the caprice cores but this is not the case -- a little torch work and some vise grips gets them right out.



^1st fitting came out cleanly with just a little solder residue left.
For those that have never taken a torch to one of the heatercores: you have to be careful with where you apply the heat. The top tank is held on with nothing but solder. If you overheat the tank, that sucker will come right off and it is very hard to get it back on without leaks.

To avoid overheating, I 1st filled the heatercore with cool water. Then I wrapped most of the top tank in soaking wet paper towels (check the above pic). Just to make sure I had everything covered, I then wrapped the core area with a insulating plumber's wrap -- several water soaked paper towels would work in place of the wrap. [This is overkill - if you are careful, filling the core with water is more than enough to protect the fins from the heat. Laying a few soaking wet paper towels on the top tank can help avoid some problems with leaks on the seams of the tank though]

Once you have the tank protected from excessive heat, apply heat with the torch directly to the tube where it enters the tank -- like this:

^If you look in the right hand side of the (fuzzy) pic, you can see vise grips locked onto the tube. Once the solder starts to melt, try moving the vise grips side to side a little - once all of the solder becomes liquid, a bit of side to side action and a straight pull with the vise grip will pull the tube out cleanly.

both tubes out with no problems:


On to the really nice bonus you get with this core -- the pre-drilled holes are perfect in size for a 3/8" -18 NPT tap. If you buy 3/8" NPT x 1/2" barbed fittings, this is a piece of cake. Just thread the existing holes like so:


Then screw in the barbed fittings. To make sure there are no leaks whatsoever, you can add some JB Weld to the threads and then let it dry or use the torch a little more and silver solder the fittings in place.

Before sealing the fittings in place it looks like this:


A tweak for better waterflow through the core:

If you look at the pic, you can see that the fittings are screwed in and they are ready to be soldered...but the ones that are in place have had the threaded section cut down (Dremel + high speed cutoff wheel) to prevent any flow restrictions.

On the far tank, one of the 3/8"npt x 1/2" barbed fittings in its original form is setting on top of the tank to demonstrate the possible problem -- when it is screwed all the way into the tank, it would be very close to the back wall of the tank -- in between the tanks you can see the section of thread that was cut off with the Dremel.

I just threaded the fittings in as far as they would go, marked em with a sharpie (sharpie mark still readily apparent on the threads of the fitting that is screwed into the 1st tank) and then cut them off leaving 3-4 full threads before the sharpie mark. That gives me a little more clearance and no concerns about overly restricting water flow.

To do this correctly, you have to screw the fittings into the tank and then mark them as each top tank is just a little different and that will change how much you have to cut off. If you cut the threads too short, you will have to run down to the auto parts store, buy some new ones and start over.

Tweakage for looks:
I cut 2 panels out of 22 gauge brass sheet and silver soldered them to the sides of the core - they are approximately 2" wide x 10.75" long. Once they were cut and propertly soldered to the core, I cleaned everything up and added primer and black paint to get this:

No more wavy sided look.

Pics of the finished '77 Bonneville core with the shroud I built and a couple of 120mm fans in place:



It has gaskets between the shroud and the core and gaskets between the fans and the shroud to make sure there is no air leakage. the gaskets are made from Vapco cork tape (basically the same stuff that chipcon calls "sealstring" in the prommie kits). Thin neoprene gaskets or the like also would have worked but i had a lot of cork tape left over from my last phase change build so I just used that.

It is fairly hard to tell in the pics, but the paint on the shroud and the core match up almost perfectly -- the angle makes them look like slightly different shades because of the metallic in the paint. When they are viewed from the same angle, they match.

Painting the core:

1. Scrub down the sides, the top tank and the bottom tank with cast aluminum wheel cleaner (basically acid) and a brass brush - rinse it off with lots of water and let it dry.
2. Lightly rough the sides and tanks with 400 grit wet/dry paper, once again, rinse with lots of water and dry off with lint free paper towels or terry cloth.
3. 2 mist coats of Duplicolor adhesion promoter as per can instuctions.
4. 2 coats of Duplicolor Hi-Build sandable primer, lightly sand between coats with 400 grit wet - if you sand thru the primer and hit metal, add another primer coat.
5. 2 coats Duplicolor Primer Sealer
6. 2-4 coats of Duplicolor Enamel paint
7. 2 coats Duplicolor clearcoat.

Let dry for about 5 days minimum if you go with the above painting scheme - putting it in out in direct sun light for a day or two will help speed up the drying. Just make sure you bring it in before it gets dark outside or the paint will likely get cloudy.

Another way to speed up the process.
1. steps 1-4 as above.
2. skip step 5 from above.
3. 2 coats of Duplicolor Truck and Van paint in whatever color you like.
4. 2 clear coats.

Bake the core in an oven at 125 deg F for 1-2 days.

100% copper core vs. Brass tanks & side panels

When you go to get the heatercore, make them pull it out of the box before you buy it. If you have already bought it and it is the wrong one, see if they will exchange it as most of the brass tanked cores are much more difficult to mod correctly.

How to tell the right one from the wrong one?
check the pic:


Both heatercores are for the same model - the '77 Bonneville with a/c.
The one on the left is clearly brass-sided with brass tanks where the one on the right has copper sides and tanks. I slipped up once and didnt check and that is how the brass one wound up in my collection.

Other ways to tell them apart -
The copper cores usually have the extra ridge that runs down the side of the core where the brass ones just have the flat ridges running side-to-side on the side panels.

The bottom tank on the copper core is usually a bit flatter and wider than the bottom tank on the brass core. The brass cores usually have a bottom tank that has a rectangular block like section on the bottom tank (check the pic). The copper tanks often have a much more rounded center section on the tank.

Both cores had the same markings on the box so definitely make them break open the box and check the core before you buy it. The tubes on the brass-sided ones I have seen are not as easy to mod as the copper ones. If there is an Advance auto store near you, check there - I haven't seen any of the brass sided ones from Advance as of yet.

My Nikon is temporarily out of service or I would have the shroud building section of this finished. The part to get the Nikon back in action should be here with in a week -- so the shroud building section is coming soon.

Side note: a properly built shroud adds more than a 40% increase in the cooling ability of a heatercore.

Bad_CEKTOP said:

Nice, I've seen this over at xtremesystems, the 77 Bonneville cores are $50 CDN here in Canada, when I get the chance to swing by a store I'm gonna pick one up.

Great guide.

Click to expand...

Thanks.

The other versions of this thread have gotten fairly messy over time so I thought it would be a good idea to consolidate it into one neat post that didn't require reading 4-5 pages to get all of the info. That and I updated the info as needed.

More info:
Soldering in the fittings. The solder used can make this process fairly simple or a pain in the arse. AutoZone carries an acid core solder that is great for heatcores. It is about $5 and it melts at a fairly low temp so you don't have to get the top tank super-hot to properly solder and seal the new fittings.

I normally use a bit more expensive version of silver solder for all the soldering I do but it is pretty much overkill for a heatercore. If anyone is interested in overkill, get Harris StayBrite8 and use it with Harris StayClean flux. It becomes liquid at 535F and it rated for around 11,000psi shear strength and 15,000psi on joints.

Torch for the heatercore mod:
Just about any propane torch will work. I used one of the Berzomatic torches that comes in the Plumber's Kit from WalMart for the first core I modded. That kit is still available with the same torch and it is around $20 with a tank of propane included.

Since then, I started using a BerzoMatic TS4000 torch and that is the one in the pics. It burns a bit hotter than the regular propane torch so it gets the job done a little more quickly. It will also work with MAPP gas so it occasionally gets put to use when I am building waterblocks or phase change evaporators.
pic of some serious heat:


pic of another modded '77 bonneville core in my bro's two room H2O system:

I deleted my post so it wouldn't split yours up
Thought's I'd get away with a repost later but you caught me.

quick question for ya. do you think you could convert it to single pass if you got more than 1 chamber for the top half and modded it. maybe even make it like a spilt loopso 2 in 2 out ?

oh and great work btw

Bad_CEKTOP said:

I deleted my post so it wouldn't split yours up
Thought's I'd get away with a repost later but you caught me.

Click to expand...

thorilan said:

quick question for ya. do you think you could convert it to single pass if you got more than 1 chamber for the top half and modded it. maybe even make it like a spilt loopso 2 in 2 out ?

oh and great work btw

Click to expand...

I have converted a couple of them - the first one I did the easy way -I just added a center-mounted exit fitting on the bottom tank. So that one had two inlets and one outlet. Surprisingly enough, that didn't really screw up the flow thru the core.

I recently got a hold of another core that is pretty much screwed for all practical purposes (fin damage) but the tanks are fine. So, I plan on using the tanks off of that one to make one core that is dual-chamber, single-pass and then I will use the bottom tank with another core to make one that is single-channel, single-pass. Basically, I am just going to switch the tanks so each core with have the same tank on top and bottom, then I'll mod the fittings as required.

It can't be any harder than brazing two '77 bonneville cores together like I did to make the monster-core:

that was about a 9.8 on the pain-in-the-arse scale....nothing quite like a core that will take eight 120mm fans though.

Excellent guide. Well written, clear and thorough.

pelikan said:

Excellent guide. Well written, clear and thorough.

Click to expand...

thanks.

Heat exchangers for watercooling have become a minor obsession for me.
I still pick up a different core or other rad now and then just to see what mods can be done to any particular model. Between core modding and building phase change, I manage to burn a good deal of time but it is always worth it - just when I think I have squeezed all I can get out of a core a new mod pops up that increases the performance. The heatercore mod for the '77 bonneville is the end result of a lot of tweaking and testing of different cores and as far as I can tell, it by far and away produces the most bang for the buck.

I have tested the '77 bonneville with various mods and shroud designs against most of the major commercial rads and it eats their lunch for a good deal less money. Besides, there is always a certain satisfaction in coming up with something yourself.

edit: there is a new core I am playing with that is just a little smaller than the '77 b'ville core that looks like it will perform within .5 C or so. It might even match it on most systems. More info on this one after I test it a bit more.

I will continue to build on this thread with the performance info gained from my modding exploits. Right now, it is just about the best, if not the best, heat exchanger you could ask for in a straight H2O loop -- but I think I can still make it a little better.

shroud building and flow mod info will becoming as soon as I finish it and get some solid test results.

sneak peak at the shroud:

that was a few hours on the CAD proggie...the results are better than I could have hoped for though.

Ive seen this somewhere before. Have you posted this guide on another forums?

Why do you think a copper core is better? Brass is much easyer to work with and brass cores still have copper finns so cooling ability is uneffected?

How did you braze the cores together without the solder melting and the core totaly disintigrating? i guss you must mean solder

Nice guide

slater..

slater3333uk said:

Ive seen this somewhere before. Have you posted this guide on another forums?

Why do you think a copper core is better? Brass is much easyer to work with and brass cores still have copper finns so cooling ability is uneffected?

How did you braze the cores together without the solder melting and the core totaly disintigrating? i guss you must mean solder

Nice guide

slater..

Click to expand...

there were various versions of this up in several forums - well, most of it anyway....some of the stuff in this thread is new.

The primary reason I suggest going with the copper core over the brass core involves the tubes on most of the brass tanked bonneville cores I have seen. They use a different method to lock the tubes into the top tank on the brass versions and it is really difficult to get them out without damaging the tanks. They are pretty much locked into the tank with a bit of a crimp and a barb - the last one I ran into like that took the torch, a dremel, a tubing cutter and a drill just to get the factory tubes out. If it weren't for that, I wouldn't have a problem with them.

the monster core...nope - I meant brazed That took alot of water, a good deal of heatsink paste and some very careful fluxing and heating. I built a jig of sorts to hold both cores in the right alignment out of weld steel and then I clamped everything in place and did the seam in 1/2" sections with safety-silv 45 and staysilv flux (2 more of my favorite products from Harris ) Once I had a solid attachment between the cores, I switched to staybrite 8 and resoldered the seams on the fins. Royal PITA material but it is leak-free.

nice guide, just one tip, when cutting the thread for the barbs, coat the tap with grease so that most of the swarf sticks to the tap and doesn't go into the core itself.

what temps are you getting with that huge 8 fan thing?? <-watercooling newb

Weapon - have you ever tested/tweaked a Fedco 2-342 (GDI 399090)?

ukdan said:

nice guide, just one tip, when cutting the thread for the barbs, coat the tap with grease so that most of the swarf sticks to the tap and doesn't go into the core itself.

Click to expand...

that's a good idea - I usually just flip the core over and blast it out with water after I'm done with it. seems to have the same end result. anyway, there usually isn't a whole lot of shavings left after the tapping as the holes are slightly larger than 9/16" which is the size normally used with a 3/8" NPT tap.

BlueMan said:

Weapon - have you ever tested/tweaked a Fedco 2-342 (GDI 399090)?

Click to expand...

I have one from a '70 on my bench right now. I am working on fittings that will get a little more flow out of it (hopefully). I also have one from another year model of bonneville that I am modding (a little smaller than the '77 b'ville but it will still take dual 120mm fans). As soon as I get all of them modded and shrouded, I plan to plug 'em into my current system to see how they compare to the latest version of the '77 bonneville core.

bah, hurry up lol I want to know which one, I hear great things about both.

Just so you know, weapon, I was able to attach my tubing to the pipes on the 2-342 without any kind of barbs - just boil the tubes and stretch them over. I imagine you can't get better flow than that!

well, there is one thing I don't like about the Fedco 2-342 (GDI 399090) - it has oval shaped punch outs for the tanks. That isn't that big of a deal to fix as I came up with a solution for that in the past. Anyone else's 2-342 have round holes where the tube enters the tank or are they all sporting the oval ones??

why fix it as opposed to just cutting off the pipes?
They pinch the inlet and outlet down to a narrow channel on both the inlet and outlet. If my damn nikon wasn't temporarily out of service, I'd post pics of the tank with the tubes removed so you could see the shape of the tubes where they enter the tanks - a little weapon moddage will get the flow on this one up a bit. I might have to do a brief how-to on modding this sucker.

anyway, I am going to put together a plexi shroud for it tonite and finish the inlet and outlet mods. I'll post pics when I get my nikon up and running.

EDIT: an old and somewhat crappy drill bit (9/16" honkin' bit) decided it had enough of my nonsense and broke at the shaft mid-core mod. Needless to say, scratch one Fedco 2-342. On the bright side, I will have some really cool pics of the guts of a heatercore when the nikon gets back in action as I went ahead and dissected this one with the dremel armed with a fiber reinforced cutoff wheel -- the number of layers of copper that are packed between the flow channels in these things is downright amazing. I'm still fairly shocked the bit snapped -- it must have already had a crack in it from drilling tops for waterblocks as there is no way the thin metal in a heatercore tank should have even slightly phased it.

of course, that bit was older than dust...

Anyway, I promptly called the local auto stores and found another 2-342 and it has been modded with 1/2" female theaded fittings (even if it ended up being a 40 minute round trip to get the core). After the slight setback, I only managed to get the top plate for the shroud cut but it is ready to have the side panels added. I cheated and used plexi b/c it is quicker and easier than the metal route. I am trying to decide if I am going to be lazy and just make a box style shroud or a nice, highspeed venturi design. Leaning towards the venturi at the moment.

side note: if you plan on having the shroud on the same side and the inlet and outlet on the 2-342, you will be a little cramped for space - the core area is 240mm long --- a dig thru my 120mm fan collection turned up 2 that are 238mm when stacked back-to-back. That doesn't leave much room for error as you only have about 1mm on either side of the fan cutouts. The inlet and outlet tubes are packed in there fairly tightly as well (especially if you add 1/2" threaded female fittings). If you mount the shroud on the opposite side, it would be much easier.

weapon, have you tried fitting the 77 B-ville core into a 5 1/2 bay? My bays are all railed and are 6" wide with about 1/8 inch internal indents for rails on each side. Just wondering how much clearance there will be, you have it down as 5 5/8.