[nUcLeArEnVoY]

Originally Posted by LKLusza

Hi Folks,

Here's the setup I currently run on my '70 400cu, auto trans and AC equipped GTO:
1) FlowKooler Cast iron HP water pump w/ tightened clearance to new SS divider plate.
2) US Radiators 4-row DesertCooler brass/copper rad with "High Efficiency" option.
3) Factory AC shroud
4) 7-blade 19" AC Clutch fan (I think it's factory- can anyone verify?) PN: 9796134
5) Hayden 2747 HD fan clutch
6) Stant 180 degree t-stat w/ bypass hole drilled in flange.

During the recent severe heat wave we experienced here in NE PA, I had an issue where the car started to run hot while stuck in traffic w/ the AC on. Temps went quickly from the usual 180-183 degrees up to 223 at which point traffic started moving again. I suspect that it would have continued to rise had I sat still longer. Temps very quickly returned to normal with any forward motion of about 15 mph or more. This leads me to believe that it's an airflow issue rather than capacity.

As a test, I switch the 2747 clutch out for the Hayden 2797 Extreme Duty unit. When mounted with my Pontiac fan (9796134), the thing refused to disengage. It whistled like a Chrysler Turbine car even on a subsequent 70 degree day. It just wouldn't disengage. Could it be that that Pontiac fan blade doesn't have enough pitch to make the clutch work properly? If not then what fan could I use?

That's exactly the issue with your new fan clutch. The severe duty fan clutch is not meant for standard passenger car fans. In fact, in terms of spec-sheet standards, even the HD fan clutch is not meant for these cars, even though most get away with it just fine (including myself). The severe duty clutch is too strong for our factory fans and will pretty much remain engaged, putting a strain on the engine which in and of itself can cause it to work harder and build heat and also risks belt slippage.

These cars from the factory were equipped with standard duty clutches, not even HD's. I would start looking into your AC setup. Issues with the AC system will come out as an engine building up heat - a binding compressor clutch requires more engine power to turn, an overcharged or undercharged system can stress an AC system and thereby engine cooling, and outdated or incorrect components can overstress the AC system. Is your condenser upgraded for what I'm assuming is an R134a conversion? Is your evap core clogged up?

Lastly, your engine tune could be contributing. What's your initial timing, and are you running vacuum advance off manifold or port vacuum (or are you running vacuum advance at all?) Higher base timing plus vacuum advance allows engines to idle cooler.

Also never hurts to verify your temps with your gauge. It's normal for AC to increase the engine temp because of the strain on the engine as well as the fan having to exchange additional heat from the condenser, and 223 is getting pretty warm but a lot of new cars won't even turn on fans until 230 or so..