Why does the fuse block melt before the fuse blows?

[DMC1983]

Our cars seem to be notorious for melting fuse blocks. My car does have a new one and is already melting. Is it because of the material used? Crappy electrical system? Inferior design? Or just a combination of everything listed? I'm sure I know the answer, I just want something a little more scientific... maybe a cure

[Bitsyncmaster]

Two reasons.

1) Corrosion with age.
2) Poor design with the pins have very little pressure on the fuse pins.

I highly recomend the new DMCH fuse block. The pins supplied really hold the fuse tight.

[David T]

Too much load on certain circuits, under-gauge wiring, inferior design and manufacture of switches, wrong sizing of the fuses and circuit breakers. Pretty much average for a Lucas inspired electrical system. A little PM (Preventative Maintenance) will go far in helping the electrical system function trouble-free. The #7 circuit is notorious because when the fuel pump goes bad and draws too much current, but not enough to blow the fuse, the fuse melts the plastic block.
David Teitelbaum

[DMCH James]

We still recommend cleaning the terminals and replacing/cleaning the fuses once a year. How many people actually do this?

James

[DMC1983]

We still recommend cleaning the terminals and replacing/cleaning the fuses once a year. How many people actually do this?

James

<--- I can think of one.

My No. 15 fuse (hi beam, correct me if I'm wrong) went last night and the fuse itself + the block melted.

[LEVY]

Most of the time, fuse block melt due to overheating by bad contact and not because of incorrect fuse. Of course, using a bigger fuse might overheat the whole system, including fuses.

On our vehicles,overheating occurs because of a bad fuse/fuse block contact. OEM buse block is not of the best quality. Newer, improved fuse blocks would have a better contact with fuses so, overheating should be a thing of the past.

The more you play with the fuses, the more chances you have to get the connections loose. To my way of thinking, removing fuses for inspection will only agravate the situation, a regular fuse block inspection would help, if you see signs of corrosion, by all means remove and clean that fuse, if everything looks fine, just check to make sure fuses are tight.




Our cars seem to be notorious for melting fuse blocks. My car does have a new one and is already melting. Is it because of the material used? Crappy electrical system? Inferior design? Or just a combination of everything listed? I'm sure I know the answer, I just want something a little more scientific... maybe a cure

[JIMJAM]

Some of my biggest headaches have come from tinkering in the fuse area. Just after buying mine like a good boy I replaced all the fuses and relays. Unknown to me when I popped in the new and improved lamda it partially pushed out a wire behind and unseen. All hell broke lose. After 3 months,a hundred post and taking the car apart I stumbled across it.
Lesson learned- Replace one thing at a time. Start and run car them move to the next.
I avoid the fuse area like its radioactive. I dont even like to look at it.
One thing I did do was cut a custom wooden cover. Easier to remove and I drilled big holes in it to allow for good air flow.
And yes. The #7 fuse area was a big melted hole when I got the car and 6 months ago even rerouted through a holder the fuse still managed to melt holder and all into a big blob. Its one of those Delorean gremlins. But twice in 30 yrs in my case I can tolerate.

[David T]

Drilling holes in the wood covers is a good idea. Leaving the cover off the fuse-block but nearby to hold extra fuses in is also good advice. Check to make sure each and every fuse is the correct size for it's position. That info is NOT on the fuse-block cover. You have to look in a manual to check fuse sizes. It is difficult to know if, when you push a fuse (or relay) in, if all of the connectors are in their proper positions or if they have moved back and are just touching and making loose contact with their terminal. Every owner should at least look in this area once-in-a-while to see if anything is melting. The fan bypass is also known to melt-down, even the one with fuses in it.
David Teitelbaum

[nkemp]

The only thing diddling with the fuses accomplishes is removing any corrosion... of which there should be none. It gives you an opportunity to check for discoloration due to excess heat but there should not be any heat at the fuse panel. You should not have to periodically remove the fuses.

Heat occurs when a voltage/current flows through a resistance. In theory, the fuse connections should be zero resistance (or very small) and as such should not generate any heat. It appears that the terminals in the fuse box do not have sufficient contact area to carry the current and thus the connection resistance is resulting in heat. And when there is sufficient heat to melt things we have a problem!

My #7 was toast. In place of replacing the whole fuse panel, I used an "extend a fuse" that is connected to a heavy duty spade terminals. I removed the original terminals from the fuse panel, threaded the extend a fuse through the #7 openings and upgraded the original female panel terminals to a heavy duty design. Some day I may replace the whole fuse panel (Santa ... are you listening?)

There is another discussion that the poor electrical grounds in the car contribute to the problem. I know for a fact, having upgraded my car to a ground bus, that the ground circuit for the pump and dash is problematic as shipped from the factory. Having improved the ground via the bus, my volt gauge no longer looks like it need a dose of Viagra and now shows truer voltage and is rock stable.

[nkemp]

Drilling holes in the wood covers is a good idea.
David Teitelbaum

In all due respect, this is like chopping a hole in the roof to let the smoke out. It solves the wrong problem

Solving the DeLorean's root problem is not letting the heat out of the fuse panel but eliminating the heat. Fuse connections should not be getting hot enough to melt things.

Either the connections should be changed or the circuits split to reduce the load per circuit. Changing the connections should do the job while maintaining the original wiring (so that future mechanics don't have to figure out what the previous owner did).

Nick

[r00b]

Newer, improved fuse blocks would have a better contact with fuses so, overheating should be a thing of the past.

The "improved" fuse blocks also melt.

[LEVY]

Then,

False advertisement! :smile:

Solid contact should not overheat!

That is why I do not recommend pulling fuses just as preventive maintenence. No matter what fuse block you use, if you keep pulling fuses just to check corrosion will make your fuse block weak.

Best thing to do is, after a drive, check your fuses for sign of overheating, if it feels OK, then don't mess with fuses!

Someone mentioned drilling holes to the wood, that might only make it worst due to the fact that battery fumes may reach the fuse box easier causing corrosion.

Levy




The "improved" fuse blocks also melt.

[DMC5180]

When Installing a new fuse box and terminals. It is important that any heat damaged and green copper is cut back to a reasonably good wire Or you could get heat resistance in the terminals anyway.

[David T]

Heat creates a viscous cycle. The hotter things get the higher the resistance. The higher the resistance the hotter things get. Doing anything to help keep things cool is good. I agree it shouldn't get so hot there but you have a lot of high amperage circuits in very close proximity with no ventilation. Making holes in the wood will have no effect on any possible fumes that escape from the battery compartment. If you have that much fumes from the battery you are overcharging the thing making it out-gass WAY too much and killing it prematurely.
David Teitelbaum