Originally Posted by Cobalteer

In much the same vein of simplicity, my plan for my early 4.2 convertible is going to be replacing the header tank.
From what I understand the new ones (C2P25607) which (as the superseding part is now the replacement for all engine types) contains a built-in "low coolant" detector, whereas my original one does not.

When, on a long run, my n/a 4.2 x350 started to leak coolant from a split (in that annoying hose that runs under the inlet manifold) it was the "low coolant" red light and warning that alerted me, not the temperature gauge, which I might to be frank have missed. I didn't really need to know the extent to which the coolant temperature differed from the norm, all I needed to know was there wasn't enough!

My car obviously has no factory wiring to support this later and improved tank, but never mind, I just plan to hook up a high intensity alarm (probably dismantled from a freezer alarm or a personal security alarm etc). Might take a 12v feed to it or for originality I might just use a little 9v battery glued underneath. If the shrieking alarm is loud enough I think I'll hear it at speed even if its tucked away under the bonnet somewhere. I'll then stop the car and investigate.

If the cooling circuit has integrity and the coolant is so hot that it is venting then I tend to find you can usually smell the antifreeze.