Reply to "Cooling system questions"

The pressure cap is (or should be) only on the surge (small) tank. The stock cap on the overflow (lg tank) is simply a vented splash-guard, as that tank is outside the pressurized circuit. You can run without it in most cases without damage.

Your trouble may not be entirely electrical. The rubber overflow/return line joining the two tanks often splits where it can't be seen. A split line may not leak and I've seen cracked metal spigots where the line is soldered to the small tank neck. Then as the engine heats up, water expands and goes into the overflow tank. As the engine cools down the theory is, a vacuum will be produced which sucks the excess water in the overflow tank, back into the small tank to resupply the engine. What often happens is, a cracked line connecting the tanks will not hold vacuum so excess water is never sucked back to replenish the engine. The NEXT time you run the engine, the water level is low, so the engine gets warmer and more expanded water is forced out to the overflow tank. By the 3rd time, you are so low on coolant- often with no external sign of a water leak- the engine overheats.

Next thing: if the pressure cap will not hold pressure, expanded hot water may also be forced out around the small-tank neck. From there it runs down the tank side, down the inner fender panel and right into a large oval hole in the right frame rail. There is no drain as-stock for this area, so the water sits there rusting the frame, until either it's all used up or finally evaporates. Driving in rain will also throw water from the rear wheels into this area. I've seen Panteras in which the right frame rail was FULL of rusty water! Fix: drill 3 recommended 1/2" dia. drain holes equally spaced in the bottom of the frame rails, on both sides. I also drill a 3/8" hole in the bottom of both legs forming the 'horse-shoe' shaped rear suspension mounts in the wheel wells.

The base of the small tank neck is well known for roughness from an unskillful factory solder job, so only a cap with a fresh, soft rubber washer will seal. Some new caps are 'fresh' enough to seal only for a month or so. The OEM Euro cap was a 0.9-bar (12 psi) assembly. We use a 16 lb U.S. cap which is slightly shorter than the Euro caps. But because it's shorter, a U.S cap will often not hold 16 psi. The fix there is to use a replacement pressure tank neck that matches the cap you will be using, and do a better job of making the soldered seal base smooth.

There are other well known problems relating to engine overheating. For instance, the Pantera radiator is 16% smaller than a '71 Corvette with the same power rating; the Pantera has poorer airflow thru the assembly, longer more restrictive water lines etc, etc. And these cars are the most messed-with-by-well-meaning-amateurs sports cars ever built. You really need a shop familiar with the car to fully solve this problem.