Hi John The stock fan-fail module (the blue thing in the relay compartment) detects an imbalance between the two fans and lights the light. If you still have it remove it NOW and replace with jumper wires. With 4 crimped spade terminals you can use the fan-fail light to tell you when voltage is being sent to the fans. As far as your question is concerned the FanZilla simply restores the proper function of the fan fail module (it does other useful stuff too). The FanZilla also replaces the single weak relay which drives the fans. My personal experience on #1458 is that it takes a lot for it to get hot enough for the fans to cut in. It stays remarkably cool most of the time. #2727 gets hot really quickly but the fans are there to ensure the radiator is cooled when there is no air-flow through it (you're in traffic). With the fans on, #2727 controls its temperature fine also (it just seems to generate more heat). It has also been spitting a bit of excess coolant out when turned off, but it has only just been put back together and things are still "settling" If you want to test the fans' function. Remove the connector(s) to the thermostat (coolant pipe, left hand side of engine bay) and short them, and turn the ignition on. Your fans should both switch on. Martin #1458 BondAtomic@xxxx wrote: > To make a long story short, I was driving in the city when the DMC heats up. > I park, and the coolant comes out the overflow. I wait, clean it up a bit, > and fill it with water. I then drive home (going a good speed to keep the car > cool.) and it was in operable temperatures. > My question? Well, the "fan fail" light is either on/off. First-the fan fail > light-that means one of the two fans isn't working, right? Or does it mean > they both aren't working? OR, does it mean one isn't working, so the other > one shuts off? > Then, if this "fan fail" light is on, is this "fanzilla" system a failsafe > device to prevent any overheating problems? I read in the tech section from > DMCJoe that the cooling system is almost equivelent of having "two > radiators." Then he goes on to describe air bleeding and such. So, is > Fanzilla the way to go? If both fans are operating and slower speeds, will > the heat stay down? > > By the by, just wanted to thank Walt for the major help in my troubles with > the passenger door, especially with those two "evil bolts of death." > > Thank you all very much. > John > 4275 >