[gumby79]

The old wives tale of a thermostat removal resulting in a worsening overheating condition, is not a wives tale it is a fact when applied to carbureted small block Chevy ,Ford ,and Dodge V8 engines ( I do not have the experience/ exposure to say whether this carries forward into the injected era). At the loacal dirt 3/8mi track guys would pull a thermostat on an overheating car and then melt the engine down.
Ask me how I know, I told him it was a wives tale I didn't believe him, when the engine hit 260 the driver pulled off the track wiped out the entire valve train( Springs lost their tension alowing piston contact) , it was a expensive lesson.

The correct answer provided by the old head at the track ,was to cut the wax module and moving element out of the factory thermostat, creating a restrictor plate of a calibrated size ( off-the-shelf restrictor plates in varying sizes are available to fine-tune a cooling system for track use allowing the same cooling components[pump ,rad] to be capable in dissipating Heat from 150 horsepower to over 800 in SBC 350" without over/under cooling). it didn't matter what class you ran, or how much power / Waste Heat you made the restrictor-plate or specialized racing engineered thermostat was always required or overheating would result from excessive flow rate/ lack of dwell time to reject it's latent heat into the radiators metal.

It's about dwell time not exposure time as somebody stated.

OP How to apply my statement to your(or some one studying to to this mod) use case. Use an old thermostat modified in the manner I described as a restrictor to stimulate a stuck full open thermostat mode of operation. Then compair. It may be too late for the A/B test modified against unmodified is returning to stock would be painful.
Another way of validating the result is to disconnect the fan let the engine reach 10° above the onset point, reconnect and measure the amount of time it takes to reach the off point for the fan ( again a little late for you to get the data for " A"test) blicking the opening is a way to cheat and get it to warm up faster for testing.
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GAPS
Were they intentional?
Absolutely they serve the purpose of ease of assembly, nothing more nothing less.

They are a defect that , at that time, were not worth the expense of rectifying(added assimblely time , more labor, extra parts) due to law of diminishing returns. However the cost is more bearable for manufacturers in 2020, as they are chasing values 3-5 places past the decimal reductions in dragged because it all adds up to a smaller number in the end requiring less fuel making it easier to meet Cafe requirements.

Anything that reduces the pressure differential across the cooling core, AKA gaps, is a reduction in efficiency.

Well done project. I have been planing to do in the future for my vehicle but I have to finish modifying the cooling stack( A/C, trans, IC , and rad) to accommodate my increased heat load at lower than factory desined RPM 1150@55mph Vs there 1800. Rad is fine but a larger Intercooler is needed to keep IAT in check.



Dream Big Chisel Down To Reality