After this Florida Summer, I may consider hack. A few extra degrees may be worth it.
It's less a "hack" than doing what should have been done in the first place. The manufacturers are SO greedy, that they will leave out an item such as a heater core flow valve due to it's costs. One one truck, it is miniscule; multiply that by, say, a million trucks, and you get the point.
I had a GMC Sonoma pick up truck came into the dealer where I worked in about 1998-ish. it was an extended cab with the then "new" Vortec 4 cylinder engine. It was summertime, and like this year, an exceptionally hot summer. This customer had just bought the truck several weeks prior and had about 3000 miles on it.
The complaint was that the transmission would disengage the torque converter clutch and default out of overdrive whilst driving down the highway.
During diagnosis, I found the trans fluid to be black, and the scanner showed the TOT (transmission oil temperature) to be a scorching 250 degrees! Doing a visual inspection, I noticed that the upper radiator hose was routed to the side of the radiator where the transmission cooler was. This meant that hot coolant was being dumped on top of hot trans fluid, both of which which had yet to cool.
The only practical solution I could think of was to install an auxiliary cooler. Well, GM doesn't (or didn't at that time) allow for installation of an accessory to fix a warranty issue. To make matters worse, there was never an external cooler offered for the S/T truck series at that time. What to do?
I had our Service Manager contact the occupants of the ivory tower and get authorization for me to field engineer this problem.
Glory be, and miracle of miracles, he got the rubber stamp for me to retrofit an auxiliary cooler for a 1/2 Ton Sierra onto this S-truck. This meant I had to drill holes in the radiator core support and modify the rear face of the plastic grill for clearance, and I had to fabricate mounting brackets.
Afterwards, I drove the truck, and on that 100+ degree day, got into Houston's quagmire stop and go traffic with a scanner. The TOT never exceeded 175 degrees!
I flushed the burnt fluid out (GM didn't pay for that, our Service department ate it for CSI) and the truck was delivered. Happy ending to the story, and Happy customer, and problem was fixed.