1/2" to 3/4" was the original design clearance; the nature of the assembly process for the 4-piece welded shroud can introduce additional variation. I doubt if what you describe is a sole cause of your issue.

 

Read thru this thread and it seems you should start from the basics, since you really don't know what you have.
Prudent to clean the system first.
DO NOT do it after installing a new radiator.
Here is an appropriate cleaner, not the flush.



Follow the directions, important to drive it hot long enough.
Prior to starting, with the existing coolant drained remove the block plugs, it will give you a good indication of the condition of the coolant passages.
Further, removal and rinsing using the plugs after flushing is essential for a proper cleaning.

Here are a couple pics, one of the block drains plugged (rather common) and another of just a small portion of the crap that was removed.
BTW, the engine was NOT overheating in S Florida and the coolant looked clean and green.

Once you start with a clean system and new rad you can more intelligently diagnose any cooling problems.

 

pressure test the cooling system at temp to see if you have a cracked head or block

 

Wow all through this thread thought we were talking about a clean block ,new or magnafluxed , hes right start at square 1 nothing else matters till that is clear.

 

Wow! I bet you're on to something!

 

Yup.

The fallacy of the water-is-moving-too-fast-through-the-radiator-to-cool argument, is the other side of the equation is ignored. That the water is also moving through the block too fast to pick up any heat. If you slow water on the cooling side to make it cooler, you also slow water on the heating side, so it gets hotter. You are going to get some delta T across the radiator, depending on the flow velocity, higher vels means lower delta T, but same on the block side, higher flows mean less heat is picked up, also a lower delta T

It is a closed system, if fluid flow velocity increases on one side, thus they have to increase on the other side.

Doug

 

OP Update


After DeWitt's finally got me all the parts (wiring harness was not shipped at first), I have removed the radiator.

Tonight I plan on finishing the install, but I cant find the port for the thermostat switch.

Where did you guys with electric fans install your temperature switch?

Also, are there any mods to the shroud that need to be done?

 

I put the thermo sensor in the T stat housing. I bought a housing with a threaded port.

Note that if this is a simple on/off switch,a nd not a thermistor for PWM controller, you may have to change your switch in the future so you fan either doesn't run all the time, or doesn't come on too late.

For an on/off, 195 would probably be my starting point.

In my 327/250 HP power '37 Ford pickup, there is no engine driven fan at all, and the electric fan almost never comes on, only if I am stopped, with the motor running for more than a few minutes, will it come on. A few minutes after I start moving again, the fan goes off.

Doug

 

I used the coolant by-pass port.

If I am not mis-taken JohnZ told me they actually run cooler when deleting the water pump by-pass anyhow.

 

Now that's a nice clean option. Thanks!

 

When you get a little time, see if you can explain that one to me.

 

When you get a little time, see if you can explain that one to me.

 

I feel for you - soon after I bought my 65 (L76 like yours) it became quite apparent why the seller only kept it a year - he had been chasing an chronic overheat problem, and then I was chasing the same problem.

He had installed electric fans, a cooler t-stat, a higher pressure rad cap, even a new rad . . . of course, none of that addressed the problem. In the first few weeks of my ownership once I discovered the problem, I tried a rigid fan set up (to rule out the fan clutch), and made sure the timing was set to specs. Still, every outing ended in overheating (per the gauge, and often with coolant puking.)

Eventually, I drained the cooling system and opened up the block drains, flushed the system and drained it completely again; put the proper 180 t-stat in there (if nothing else to rule out a non-functioning t-stat); replaced the nearly-new copper / brass rad that the p.o. had installed with a new Dewitts rad in there (exact repro of the Harrison stacked plate aluminum rad the SB C2 came with), tried a few Wells sending units until I got one that was telling the truth to my temp gauge (using an IR gun), ditched the electric fans and installed a new and proper fan clutch with correct fan; installed a new [rebuilt correct] water pump; and of course a new lower rad hose.

I am sure there are a bunch of postings from me on this forum in 2003 which outline this saga.

Problem solved, and I no longer glance nervously at the temp gauge every minute or so. I think the biggest impact was the Dewitt repro Harrison stacked plate aluminum rad, which has ~ 25% greater cooling capacity than the same sized copper / brass unit that I had in there. Plus, Tom Dewitt himself helped me sort out some issues I had during the install - a super guy.

If you have tried everything (timing is correct, water pump is operating as designed, cooling system has been flushed thoroughly to ensure no partial blockage inside the coolant passages in the block or manifold; fan clutch is new or has been ruled out, fan itself is the proper one; lower rad hose is not collapsing; proper amount of coolant is present), and you have confirmed with an IR gun that your car is truly still overheating, then I definitely agree you need to revisit that radiator you have in there now - whether it's not capable or it's not functioning as it should. I see you have gone ahead and gotten Tom Dewitt involved - good call.

 

:This is it you hit the nail on the head I kept telling people that you dont need the flex fans and all that extra ******** on there. I had same problem and went back to the way it was design to work Good post

 

If you are running a/c in hot climate that electric fan sure makes a difference.

Mine is set up to factory standards. And works as intended.

But no way it will sit in traffic at 95 degrees with a/c on without it climbing over 200+ without the SPAL fan. I don't get in traffic much. But I do use the fan fo a cool down after stopping.

 

Thanks for the input. It's good to know that a similar situation was resolved with a DeWitt's radiator.

I wish I could have got some input from Tom DeWitt the way you and others have been so lucky to recieve. My experiance with their company is average at best. Shipping updates and tracking numbers would have been nice. The lady who always answers the phone is nice, but not very knowledgable with technical questions. I also had the wiring harness miss the first shipment and had to wait three days to get it. At least the shipped it out first class. Let's hope their product is as good as everyone says it is.

 

I was able to get him when I had a technical question. You could always ask to speak with him. He also responds here on the forum.

 

Good to know. Hopefully all I have to say is "Thank you" after installing his radiator.

 

My experience - the correct fan shroud, correctly installed (and perhaps all gaps insulated as you get with an A/C car) in conjunction with the correct fan, positioned correctly on a fan clutch (which locks up per spec) keeps a C2 Corvette from running too hot on a hot (90 degree and +) day. Even when I had an A/C compressor on my car (VA, since removed).

I'd politely suggest that these cars, when new, were capable of being run on a hot day with the A/C on without overheating. Hence my decision to "return everything to oem condition" to put the overheating situation behind me, which worked for me.

 

Nope. You didn't hear that from me - must have been someone else.