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  We're Havin' a Heat Wave

  Jul 18, 2024

  Note: The picture above shows a modification to an engine fan clutch as described by Lust4speed , a member of the Performance Years (Ames Performance Engineering sponsored) Pontiac forum.  The picture is his work. 

  Recently, we experienced an excessive heat wave for an extended period.  90° to 100°F.+ for more than a week straight and high humidity to go with it.  6AM air temps were as high as 80°F.  As you can imagine, with air temps that high, the pavement temps out on the street were ridiculous.  This period of hot weather revealed a weakness in the GTOs cooling system that had historically not been seen.

  Previously, I had installed a Flow-Kooler^tm high-performance cast-iron water pump and a stainless-steel divider plate with tightened clearance.  Along with that I upgraded the standard 3-row factory AC radiator to a 4-row Desert Cooler^tm radiator from US Radiators that also had the "High Effeciency" copper/brass core.  The car already had the fan shroud appropriate for AC equipped GTOs, as well an authentic Pontiac 7-blade, 19” diameter fan (p/n: 9796134), a Hayden 2747 Heavy Duty fan clutch and a 180° thermostat (the GTO left the factory with a 190° thermostat).  The increased capacity of the cooling system in general, along with the greater efficiency of the pump and radiator design, had the engine operating at ideal temps consistently, right up until the heat wave arrived. 

  While I had the GTO out during one of these extra hot days, enjoying my newly converted AC system, I found myself forced to take a detour due to downed power lines.  I, along with everyone else, were shunted off to an already busy highway.  Waiting in a long line for my turn at a traffic signal, I noticed the engine temps slowly but steadily start to rise.  Before traffic started to move again, I saw the temps rise from 185° to as high as 223°, with no end in sight - a previously unseen behavior when at idle in traffic. 

  When I was moving along once again, the temps immediately started to come back down.  It was apparent that any forward motion, even as little as 15-25mph, was enough to cause a reduction in temperature.  While I had more than enough cooling system capacity, this behavior indicated that the system suffered from insufficient airflow when the engine was idling at a standstill in excessively hot weather.

  Drawing from my street rod cooling system experience, I chose to change the antifreeze-to-water ratio from the standard 50%-50% mix, to 75% water and 25% antifreeze.  I would then augment that mix with the WaterWetter additive.  This compromise keeps the GTO protected from freezing down to 5°F. and boil over to 257°F.  It also provides more water with which to add more WaterWetter.  WaterWetter is a Redline Oil product designed to help increase the coolants surface contact ability so it can absorb and transfer more heat, more efficiently.  The reduced antifreeze levels still retain the necessary corrosion protection but provide the maximum cooling potential of the coolant itself.  I believe it to be an acceptable arrangement for a 3-season automobile that’s stored in a climate-controlled garage.

  Next, I removed the fan from the car and separated the clutch from the fan itself in order to perform the modification described by Lust4speed (pictured above).  It involves moving the end of the spring from the factory position, and unwinding it slightly, by about 1/16” or slightly more, and re-anchoring the spring end.  Allegedly, the ever so slightly loosening of the winding in the thermal spring will result in earlier activation of the clutch so that it engages sooner.  Theoretically, this would increase airflow at a time when the engine needs the additional airflow the most – idling in hot weather at low rpm with the AC on.  Lust4speed does caution, however, that changes are likely to be trial and error as excessive adjustment would cause the fan to not release at all when it's no longer required.  The fan clutch modification, paired with more efficient coolant, is the best I can do with an otherwise stock-ish cooling system.  

  On a much warmer day, I took the GTO out for a drive of about 15-20 miles or so and stopped in a gas station.  I left it idling with the AC on full for about 15 minutes in the paved parking lot. The engine temperature the EFI was seeing never got above 219°.  A little cooler would have been better, but I'll take this as a win for now.  Of course, temperatures dropped immediately once I was in motion again, eventually coming to 180°-183°.  Unless we have another record heat wave, this will be more than adequate for my needs.  The “Plan B” would be to install a high performance 170° thermostat from Rische Performance and shift to a modified Hayden 2797 Extreme Duty clutch.   We'll see.

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