Topic: Where can I find a 40A fuse for my FoMoCo fan?

[neale_rs]

My main point is that the heating of a resistor (or a section of wire) is related to the watts, not just the amps.  This is why the voltage drop across different sections of the wiring is important to consider.  The sections with more resistance will be dissipating a higher proportion of the watts (heating up more).

[sharpxmen]

My main point is that the heating of a resistor (or a section of wire) is related to the watts, not just the amps.  This is why the voltage drop across different sections of the wiring is important to consider.  The sections with more resistance will be dissipating a higher proportion of the watts (heating up more).

ok, you're right but i still don't understand what's that got to do with where you locate the relay

[neale_rs]

Let's say you have a circuit that is just a battery with a thick (relay) wire and a thin (fan) wire in series.   The thin wire will melt first.

Next you could try making the thick wire longer and the thin wire shorter.  This would result in less power dissipation by the thin wire.  Sounds good so far but...

Since the thin wire is shorter its ability to dissipate heat will also be reduced in proportion to its length. 

I did some calculations and it turns out that the power dissipation per inch will not be reduced unless you make the thick wire very much longer, enough to make the total resistance greater than in the original circuit. 

So you are right, I was wrong, putting the relay closer will not usually help.  Also, if all the wires are of the same gauge, the location of the relay will not matter.

[sharpxmen]

Let's say you have a circuit that is just a battery with a thick (relay) wire and a thin (fan) wire in series.   The thin wire will melt first.

Next you could try making the thick wire longer and the thin wire shorter.  This would result in less power dissipation by the thin wire.  Sounds good so far but...

Since the thin wire is shorter its ability to dissipate heat will also be reduced in proportion to its length. 

I did some calculations and it turns out that the power dissipation per inch will not be reduced unless you make the thick wire very much longer, enough to make the total resistance greater than in the original circuit. 

So you are right, I was wrong, putting the relay closer will not usually help.  Also, if all the wires are of the same gauge, the location of the relay will not matter.

i see what you were trying to say now, i wasn't even thinking different lengths, i was thinking it's always the same and just the relay be by the battery or by the fan.

[jfrabat]

Bought one of those fancy laser temp readers at Harbor Freight last week so I can measure the temp where the sensor is to dial it in.

Fancy reader at Harbor Freight?  I did not know they carried any fancy stuff...

[Sherpa]

How i solved my problem

Referring primarily to power tools, a good friend of mine used to always say, "Air is our friend; electricity is to be feared and respected."  I have taken that phrase to heart and it has served me well over the years.  As such, I wasn't exactly enamored with installing fuses of a higher capacity than the wires they are supposed to protect.  To make matters worse, I was under the gun: I needed to get this thing fixed immediately so I had a way to drive to work today.

In the end, I stopped in at my local AutoZone to see their selection of aftermarket fans.  They had ones as large as 16" on the shelf, so I bought one and swapped it in place of my Ford fan.  (At $65, it wasn't much more expensive than the wrecking yard fan.)  All my wiring modifications remained unchanged.  With that, I now have a fully functional electric fan.  Even after dozens of on-off cycles, all the fuses are happy and intact.

And you guys were right: the engine is so quiet now without the mechanical fan.

[Bounty Hunter]

Glad you're on the road again.  It's been my experience that parts-store fans don't last as long as OEM fans like the Taurus, they just don't seem to be made as well, not as heavy.  I always lost the bearings in short order.

[Mozman68]

Fancy reader at Harbor Freight?  I did not know they carried any fancy stuff...

Chinese is fancy, right??

[Sherpa]

It's been my experience that parts-store fans don't last as long as OEM fans like the Taurus, they just don't seem to be made as well, not as heavy.  I always lost the bearings in short order.

On the surface, I tend to feel the same way.  I did once use a similar aftermarket fan (also purchased at AutoZone) in a project car and it served me faithfully until I sold the car two years later, but I appreciate your concern.  I am still not opposed to trying to make the Ford fan work (especially due to its near-perfect shrouding), but it'll have to wait until I can afford to take the Jeep out of service for a few days--right now the Thunderbird isn't legal to drive, so the Jeep is all I have.