IMPORTANT TECH INFO from Dakota Digital. I have the 17" two speed fan in my 440 6bbl 70 Roadrunner from the same manufacturer as the 16" two speed fan in the GTO, that fan failing to keep the 421 Tripower from overheating on the Interstate.
So my tech support epiphany doesn't get unread, I learned in setting up the Dakota Digital PAC-2800BT electronic fan control module today in my Roadrunner that any TWO speed fan that requires BOTH 12 volt power wires to be energized in order for high speed function to work, the PAC-2800BT "FAN MODE" options (Single/Two/Dual) MUST be set to "TWO" in order for the high speed function to engage. This may not be a surprise or help to anyone, but it was for me.
The 16" fan in the GTO likely never ran in high speed mode.
I realize that many discount any "fan" contribution or detriment to temperature control once the vehicle speed goes beyond 40 or 45 or more miles per hour, BUT the overheating problem I've been experiencing has been primarily at highway speed, AND I have been able to GREATLY REDUCE the temperature reached with each of two mechanical fans I have tried, the factory clutch fan, and the 17" FLEX FAN that is currently on the 421.
After struggling with coolant temperatures climbing over 225 degrees or more, primarily at speeds over 50 MPH, and trying 2 different fan and shroud assemblies, one from Cold Case (the radiator manufacturer) that's a dual 12" fan setup, and when that failed to cool acceptably, a highly rated and recommended 16" two speed fan and shroud. The only viable solution I have found so far is using a mechanical fan exclusively. The flex fan kept the "around town" temps in the 180s to 190s and the highest Interstate temp, AC ON, was 205, but mostly 198-203, and back in the 180s-190s after exiting the highway. Anyway, day after tomorrow is when I hope to spring the Roadrunner from "shop jail" and I'll be able to find out if the 17" 2 speed fan, that I know is set up correctly (because I DID IT) keeps my warmed over 440 6bbl cool, or if I have overheating issues like in the GTO. I suspect that it will work fine, and if so, that will press me even more to look at the gap as the problem with the GTO.
If I try the 16" electric fan again, after maybe finding the gap in the water pump to be too large, closing it down to 1/10th" and seeing a 8-10 degree drop in temperature, I will know how to set it up to work properly.
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