The single 16" SPAL 2049 on the car now has actually done a good job when driving around town, AC on or not. 75% sure that the issue now is the shroud it's mounted to...

 

Small update. I have a new aluminum shroud solution with flaps (8 of them!) ready to go into the car. I'll get the car back on ramps tonight (been cold around here the past few days) and will work to get the old shroud out and the new one in. We aren't supposed to get up into the 80's in temps again until mid-next week. I'm kinda hoping we get one more 90*F blast so I can really test the system again with the new shroud, but mid-80s should at least give a good idea if this is going to work or not.

Fingers crossed.

 

Well, the shroud I purchased with the flaps/holes already drilled and cut was a no go. The shroud was about .75" too tall and the mounting flanges wouldn't line up with my radiator. I tried a few other designs from some other brands and even ordered a different radiator to see if any of these shrouds would line up, but the radiators were either too short or all of the shrouds were too tall. I didn't lose any money on these things, only some time trying to match them up. I don't know how to weld and don't really have the space or tools for big time fabrication. I'm sure some flanges could have been welded to the top and bottom of the radiator to get an off the shelf shroud option to fit (like an Allstar Performance, Top Street Performance, or even a Summit Racing one), but that wasn't an option for me. A couple local speed and custom shops quoted me something north of $650 to essentially remake a shroud without louvers and with the flap provisions. No thanks.

I called Leadfoot Racing (shroud maker and Champion Rad distributor) and asked if they would be willing to make a shroud for the rad that didn't have the louvers and that had the flap cutouts. They sell other shroud designs that have the flap provisions. They also offer customization services for the Champion radiators that they sell. They are willing to hack up and customize a radiator for people (for a fee) but they weren't willing to change the design of the shroud that they supposedly make. ...right. Thanks guys.

Oh well. So I bit the bullet and modded my Ledfoot Racing shroud with the louvers. I measured my blank spaces and determined I had enough room for 4 flaps on either side of the fan. Each flap could cover two 1 7/16" holes easily and still have material left to support the flap and keep it from getting sucked inward. This is what I came up with...



I was a bit careless when I took the shroud out and the a-arm bolt put some scratches in the shroud. A scuffing with a scotch brite pad, some primer, and some DE1634, and this was the end result.



Same paint as most of the front engine parts and accessories so it should blend in nicely.

I'm giving the paint another day to fully cure (kinda cool and humid here) and I'll slip it back into the car with the flaps either tonight or tomorrow night. We're getting up to 75* on Friday and I'm off, so hopefully I'll learn something that afternoon.

 

Flaps mocked up. Paint wasn't quite cured enough for me last night (could still smell the solvents gassing off of it) so I let it sit one more day. It goes back in tonight.

 

Apologies for the delay, but I have good news. I am reasonably confident that the hex has been lifted from my '80's cooling system! I'll call off the witch doctor, medicine man, and priest that I had on stand-by. After getting my modded Ledfoot Racing shroud back into the car, I took the car out on Friday, November 17th for another test run. Ambient temps were around 78*. It wasn't a perfect test, but until we get another 85*+ day, it's what I've got. The water temp would settle to around 185* +/-3* while cruising at freeway speed. Perfectly acceptable with a 180* thermostat. A/C would bump that up by a degree or two, but it wouldn't keep creeping up. FINALLY! The fan also had no trouble pulling the temps back do to the "off" temperature of 190* when they would creep up at a light or in traffic. The flaps do hang open a little bit when the car is sitting on level ground because of the backwards rake of the radiator. My Spal "2049" (2,000ish CFM) will pull the flaps closed and suck air through the radiator without issue when it kicks on. The black paint on the shroud helps to camouflage the flaps and gives it a bit more of an "OEM" look under the hood. I dig it.




I've also driven it to work a few times in ambient temps below 55*F. Last Wednesday the 22nd and today, the 27th. The fan had even less trouble pulling the temps back down when stopped or in traffic thanks to the cooler air. On the freeway, the water temps will get sucked way down and will slowly cycle between 165*-173*. The 3-row Champion radiator is doing some work! The car has NEVER, and I mean NEVER, run this cool before in cold temps. Even with the old scaled-up radiator and factory fan setup, the coolest it would ever see in cold temps would be ~182*F. I'm taking this as evidence that the modded shroud with the flaps and holes is now allowing the new radiator to breathe properly. I still want to drive it again on a hot day to make sure the curse is gone, but I think we've got it!

I will update this thread in the future when I get another hot day to drive it.

Potential Conclusion: I traded a problem that created my symptom of hot weather freeway temp creep for another problem that created the same symptoms. I traded an inefficient scaled-up (bad) copper radiator and factory (good) shroud and fan setup for a new, efficient aluminum (good) radiator and flat shroud (bad) and electric fan setup. The old radiator couldn't shed the heat the engine was producing, and the new shroud was choking or stalling the airflow through the radiator at freeway speeds. Adding vent holes and flap covers to the shroud seems to have been the answer.

I know this has been a thread full of long, detailed, and probably excessively wordy posts, but I greatly appreciate anyone who took the time to read and offered help or advice to track down and solve the problem.

Friday the 17th was the day before my 36th birthday, so I drove the car over to In-N-Out for a treat (double-double animal style, extra grilled onions, no rabbit food, medium Dr. Pepper) and then to my favorite cigar lounge for a victory dance...

 

Thanks for following up with a successful conclusion!

I'm glad someone got the diagnosis right in post 8, and that the fix worked.

Tell the folks that sold you the baking sheet to change their design. Or sell your own baking sheets with flaps!

 

Fantastic!. Been down this route but never had a cooling problem with the electric. At the end of the day the dual fan electric setup on my 406 FI sb in my 81 from years ago didn't cool any better than the factory belt driven fan with an aluminum Rad.
Mt current stock L82 with an Aluminum Champion Rad. barely gets to 180*on a hot summer day.

 

I also run a Mark VIII on a generic aluminum radiator and have been for like 17 years (wow). It does not come with flaps or anything so I'm not sure how it works so well but it does. I replaced the motor on it once (cheap from rock auto) because I thought it had a problem but it turned out to be poor contact on the control fuse. Oh well--- I have a spare motor for the fan now. I've been quite happy with it overall but if I were to do it nowadays I'd probably get a C5 fan pair as mentioned earlier.
If anybody is looking for a single fan I would recommend the Mark VIII. You can see how it's built here from a post when I was replacing the electric motor. No flaps and a wide open support structure.....so not sure how they do it considering lots of fan assemblies have quite the shielded shroud.
https://www.corvetteforum.com/forums...post1600032492

 

VW used the flap solution in its early watercooled days.

 

I will never forget Duntov's comments.
It was a Car & Driver road test of new 1970s, an LT-1 and an auto LS5.
Duntov said the LS5 started to run hot with the A/C on at continuous 140mph speeds!
He had the fix on the shelf: "a shroud with flaps"
But the accountants nixed it!
I guess accountants don't drive Corvettes, or 140!! LOL

My bad...it was the 71 models...

 

My SPAL "2049" fan is powerful enough to pull the flaps closed when it engages. I've experienced no issues with the flaps hanging at the angle that they do. I don't know if the flaps will ever fatigue enough to a point where they can't be pulled back to the shroud. If they ever do, they are cheap and easy enough to replace.