Possibility of GMT-400 radiator swap for large 34x19 squarebody radiator?

[cal30_sniper]

Howdy Gents,

I figured I would post here before I attempt to blow a bunch of money on something that may not fit. First, a quick background on what I'm up to. I'm currently knee deep in an 8.1L swap on my '86 C20 Suburban (to mate with the NV4500 that already made it in there). Along with the 8.1 are a few performance upgrades, which I'm fairly confident are going to push my already struggling cooling system over the edge. I tow with this thing a lot, and I like to use the A/C, and I live in very hot places most of the time.

The truck was a factory 454, and has a couple-of-year-old Autozone CU730 radiator in it (replacement for the large 28x19" 4-core HD cooling radiator that came in my truck). I already have the brackets and shroud for the later 88-91 R/V 2500/3500 big block and 81-87 6.2L diesel truck radiator, which has a 34x19" core. The diesel radiators have larger radiator hose fittings, but the external dimensions appear to be the same. For reference, the common part numbers (Autozone/Spectra) are:
CU744 (big block gasoline radiator)
CU850 (6.2L diesel radiator with larger radiator hoses and engine oil cooler)

Now, the CU744 is still available in copper brass, but the CU850 is only available in aluminum/plastic now. I don't want another aluminum/plastic radiator, but I do like the idea of an internal engine oil cooler to match up with the 8.1L oil cooler ports. I also like the idea of a completely aluminum radiator, but I'm not touching one of the eBay jobs with a 10-foot pole. They have a reputation for leaking, and my truck gets used hard, both on and off road. I've run both BeCool and Griffin radiators in the past, and was highly impressed. Here's the problem, neither of them make a radiator for the larger 34" core fitment. My proposed solution? A GMT-400 radiator.

The core dimensions appear identical to the large squarebody radiator, and they both use the same saddle style mounts, same radiator hose location and size, and same size tanks/overall dimensions from what I can tell. There isn't a single specification I can point to on the big block GMT-400 radiator that isn't nearly identical to the large squarebody radiator.

Has anyone ever tried this conversion? Both BeCool and Griffin make 34x19" core radiators for the big block GMT-400, and both of them make options for an internal oil and transmission oil cooler. I don't need the trans cooler, but I could easily take out my power steering cooler from the front of the grill and port the hydroboost lines over there for better warming/cooling. I would really like to get the large 11x11" oil cooler out from the front of the engine and move it into the radiator, both for the better liquid to liquid heat exchange, and for quicker warm oil temps on my frequent short daily drives. I know a bunch of you also mess with GMT-400s, surely someone has looked into this before.

Please, just to reiterate, I'm not interested in the smaller 28x19" core squarebody or small-block GMT-400 radiators, just the big 34x19s like the factory diesel/late-big block squarebodys and big-block/diesel GMT-400s came with. For reference, some of the part numbers I found are below:

CU744 (Copper Brass Squarebody big-block radiator, 34-1/16 x 19-3/16 x 2-7/16" core)
CU850 (Aluminum/Plastic Squarebody diesel radiator, 34 x 19 x 2-1/4" core)
CU1696 (Aluminum/Plastic GMT-400 big block radiator, 34-1/16 x 19-7/16 x 2-3/16 core)
CU1521 (Aluminum/Plastic GMT-400 big block radiator 34 x 19-1/2 x 2-1/8 core)
BeCool 60069 (Aluminum GMT-400 big block radiator 32 x 17 x 2" core, has smaller core, but larger tanks that appear to result in the same overall size of 40" wide as the other radiators)
BeCool 66069 (same as 60069, but with internal oil and trans cooler)
Griffin 6-90197 (Aluminum 94-98 GMT-400 big block radiator 34" x 18.75" x 2.69" with oil and trans cooler)
Griffin 6-90198 (Aluminum 88-93 GMT-400 big block radiator) (I'm not sure why Griffin has two parts numbers with a year split, probably a different type of fitting somewhere)

The BeCool 66069 or Griffin 6-90197 looks like exactly what I'm looking for. I'm guessing that the dimensions are close enough that the GMT-400 radiators should work with minimal fitment woes. In fact, I'd be willing to bet that the main differences is the oil cooler and trans cooler hookups, which is why they aren't listed as direct fits for the earlier vehicles. Would anyone care to confirm, deny, or at least comment on that theory?

Thanks,

cal30sniper


(Pic for a little bit of motivation)

[cal30_sniper]

Well, no one replied, but I'm following up in case anyone else down the road is interested in doing something like this.

I ended up picking up a large GMT-400 radiator off of craigslist for $100 to test out. I drove over to pick it up assuming it was a 34x19" core since it was listed as from a 7.4L Vortec truck. However, the tape measure shows the core to be 34x20-5/8", which is the larger size found in the later 3500HD trucks with 7.4Ls (the 8.1L 3500HDs got even larger radiators). I figured at that point, I'd already driven that far, so I'd pick it up to test out and see how close it was to fitting.

The first attempt I used the diesel squarebody radiator brackets and shroud, along with the full rubber mounts top and bottom. It fit perfectly in width, but was understandably too tall to work as intended with the diesel fan shroud. However, with the lower rubber mounts removed, and the upper rubber mounts retained, the radiator was a near perfect fit. I think I'll run it this way, with some bicycle innertube and small rubber screw in stops at the bottom to hold it in place fore and aft, and keep the radiator from rubbing directly on the core support. I'll utilize the internal oil cooler for my 8.1, and port my hydroboost return over to the trans cooler on the passenger side. That way I can get rid of the extra coolers I've been running in front of the condenser and clean up my grill space a bit.

A 34x19 GMT-400 radiator would be a direct drop in. The 34x20-5/8 radiator requires some massaging, but also fits. Eventually I plan on ordering a nice all-aluminum unit, but I'll likely run this setup for a while and see how it works first.

[cal30_sniper]

Also of note, GMT-400s come with two different filler necks, one short, and one raised. Based on the fitment of this radiator (short neck), I would recommend using the raised filler neck if given the choice. The short filler neck fits, but the cap is pretty close to the brackets. A raised neck would make the cap easier to get on and off.