Rad Fan Electrics - 79 400GT

It is caused by a poor connection creating higher than normal resistance across the connection.
The power dissipated in the connection is current squared x resistance. If the resistance increases then the power dissipated (heat) in the connection increases. An increase in resistance in a connection from 1 Ohm to 2 Ohms will double the amount of heat generated in the connection. Once it starts it is a downward spiral as the heat build-up further oxidises the metal in the connections increasing the resistance & thus increasing the power dissipated in the connection.
If any electrical connections show signs of tarnishing/oxidisation replace them as they will only get worse. In cars of our age there will be a lot that could do with some attention.

Cheers Al

 

Good day Faber,

Al's explanation is spot on.

Also, over time the bullet style fuses become problematic, as the fuse ends and fuse block clips tend to oxidize over time. The reason being is that the clips lose there compressive strength (metal fatigue do to age/heat) which allows oxygen into the contact area... which increases oxidation/resistance causing a voltage drop... and thus heat generation and a reduced voltage to the load... overall, not good things. At a minimum I would check all your fuses, clean the ends (brass brush, etc)/clips, and lightly "Pinch" the clips together. As for a long term solution... I am looking at the block design to see if I can modernize them like I did for the Boxer/308 blocks (you can see my analysis/design thread in the Boxer section). If I can come up with something I will post up here.

Cheers,

Sam

 

Faber
Find my post from about 3 years ago about installing relays directly at the fans. I installed a fuse block behind the battery with power direct from battery, with one fuse per fan. I used the "power" circuit from the relay panel to the the control signal to the relay. The new fuses supply all the running power with no power loss thru the relay/fuse panel. Installation is neat, virtually invisible and just a few hours work. I bet my fans run faster too.
Ken