Recommendation for new radiator and elctrical fan for 280Z

[Zed Head]

VR is short for voltage regulator.  14.5 volts is good, using a good meter.  The dash gauge is isn't very good.

 

I only asked because it was undefined.  One man's "way over" is 16 volts, anothers is 14.5  I'm a numbers guy.

[Captain Obvious]

Well that's a bummer. So looking at that fuse and the cover, here's my forensic analysis of the whole situation... (Warning... Heresay and theory alert) 

 

You have (or had) a dead short somewhere in your parking light system. That dead short occurred spontaneously as you were driving. Hit a bump? Something maybe that had been very close to shorting for some time finally picked last night to be the time when it went the rest of the way? Or maybe it's related to the electrical work that you have been doing recently?

 

That spontaneous dead short blew the fuse so violently that you ended up with arcing sparking inside the glass tube along with ionized air and metal mist from the vaporized fuse material. That ionized air and metal mist allowed an arc to form (just like welding) and that arc not only allows current to continue to flow, but it also produces mucho heat. Certainly enough heat to crack the glass and melt the fuse block plastic.

 

So, you've got this dead short in your parking light system and a fuse that is still passing huge current even though the metal strip is long gone. You're pulling many amps through the dead short, and because of that, your headlights go dim (which looks to you from the driver's seat like they went out completely).

 

Then after some period of time, the arc finally stopped. Maybe the fuse metal burned back so far that the arc could no longer be sustained. Maybe when you flipped the headlight switch back and forth a couple times, you were able to break the arc? Maybe whatever shorted in the first place became spontaneously unshorted? Maybe the high current melted and opened a wire somewhere?

 

In any event, the high current draw stopped, your headlights were able to come back to better brightness, and everything else, other than the parking lights, went back to normal.

 

And for those of you who are wondering "OK, so if this is all true, then why didn't a fusible link blow?" Well here's why... For whatever reason, in Datsun's infinite wisdom, there are a bunch of circuits that hang directly off the alternator with no fusible links between the alternator and said circuits. They are a direct connect to the alternator, and in the case of a hard fault, are happy to suck down as much current as the alternator is willing to produce. I don't know if this is a design oversight, or on purpose for some reason, but that's the case, and yes... The parking light system is one of these "non-link protected" circuits.

 

So, my first question is... Is the short still present, or did it fix itself as mysteriously as it occurred?

 

You can't simply check with an Ohmmeter because all the bulb filiments will make it look like a short to ground (even though it might not be). I would put a new fuse in that spot (like a 5A fuse?) and turn the parking lights on while you watch that fuse at the same time.

 

if the parking lights come on like normal, then you've unfortunately got a continued mystery. If that fuse goes up like a flash bulb, then you need to start disconnecting things until you find out why.

[Marios280Z]

Well that's a bummer. So looking at that fuse and the cover, here's my forensic analysis of the whole situation... (Warning... Heresay and theory alert) 

 

You have (or had) a dead short somewhere in your parking light system. That dead short occurred spontaneously as you were driving. Hit a bump? Something maybe that had been very close to shorting for some time finally picked last night to be the time when it went the rest of the way? Or maybe it's related to the electrical work that you have been doing recently?

 

That spontaneous dead short blew the fuse so violently that you ended up with arcing sparking inside the glass tube along with ionized air and metal mist from the vaporized fuse material. That ionized air and metal mist allowed an arc to form (just like welding) and that arc not only allows current to continue to flow, but it also produces mucho heat. Certainly enough heat to crack the glass and melt the fuse block plastic.

 

So, you've got this dead short in your parking light system and a fuse that is still passing huge current even though the metal strip is long gone. You're pulling many amps through the dead short, and because of that, your headlights go dim (which looks to you from the driver's seat like they went out completely).

 

Then after some period of time, the arc finally stopped. Maybe the fuse metal burned back so far that the arc could no longer be sustained. Maybe when you flipped the headlight switch back and forth a couple times, you were able to break the arc? Maybe whatever shorted in the first place became spontaneously unshorted? Maybe the high current melted and opened a wire somewhere?

 

In any event, the high current draw stopped, your headlights were able to come back to better brightness, and everything else, other than the parking lights, went back to normal.

 

And for those of you who are wondering "OK, so if this is all true, then why didn't a fusible link blow?" Well here's why... For whatever reason, in Datsun's infinite wisdom, there are a bunch of circuits that hang directly off the alternator with no fusible links between the alternator and said circuits. They are a direct connect to the alternator, and in the case of a hard fault, are happy to suck down as much current as the alternator is willing to produce. I don't know if this is a design oversight, or on purpose for some reason, but that's the case, and yes... The parking light system is one of these "non-link protected" circuits.

 

So, my first question is... Is the short still present, or did it fix itself as mysteriously as it occurred?

 

You can't simply check with an Ohmmeter because all the bulb filiments will make it look like a short to ground (even though it might not be). I would put a new fuse in that spot (like a 5A fuse?) and turn the parking lights on while you watch that fuse at the same time.

 

if the parking lights come on like normal, then you've unfortunately got a continued mystery. If that fuse goes up like a flash bulb, then you need to start disconnecting things until you find out why.

I like your theory and in many cases you have mentioned I've been thinking the same things.

 

Last night when I found the fuse, I have put a new fuse (the same amperage, 15A) and with the engine off I first turn the positions lights on, so 4 markers  plus the front dual purpose light. Watched the fuse for red glow, but there was nothing. So I got braver and turn the headlight switch one position further to turn head lights and rear lights, at which point I took cover in case of spontaneous inferno...Luckily (or maybe not so) there was nothing happening... This morning, whether it was smart move or not, I decided to drive the car to work. I left the fuse box cover off so I could monitor the fuse. I probably spent more time looking for a red glow on fuse than I looked at the road. Nothing happened. No problems. I suppose I should now go and examine every light that is on this circuit and clean the connections. 

[Zed Head]

That fuse must have been defective or of poor design or both.  A proper fuse of that design typically fails with absolutely no drama.  Most people don't even realize it's blown unless they inspect it closely.  No smoke, smell, heat, or burn marks.  Just a missing filament.

 

And many amps through a dead short will melt the wire insulation.  You'll get smoke and smell then.  I would check the wire on the back of the fuse box that attach to that fuse terminal.  It's probably melty looking.  Follow it up in to the harness and you might find the short.  It's probably waiting for the right bump.

[Marios280Z]

 I would check the wire on the back of the fuse box that attach to that fuse terminal.  It's probably melty looking.  Follow it up in to the harness and you might find the short.  It's probably waiting for the right bump.

 

Will do.

[Captain Obvious]

Well the biggest bummer right now is that if the problem spontaneously went away, you can be sure that it will spontaneously come back again.

 

Are you double dog sure it doesn't have anything to do with the electrical work you just did? You were messing around up front near the parking lights with the fan install. I know it's unlikely, but just seems too coincidental.

[Marios280Z]

Last night I pulled out the fuse box to take a closer look at the wires coming into i. NONE of them looked like there was any type of failure. All good, not burned isolation, nothing. Chased it as far as I could to where it went into harness, and I still couldn't find anything. 

Considering how hot the fuse burned down, is it possible that the shortage took place somewhere else down the harness other than fuse itself? I was expecting to find melted wire at least in the vicinity of that fuse.

 

 

Well the biggest bummer right now is that if the problem spontaneously went away, you can be sure that it will spontaneously come back again.

 

Are you double dog sure it doesn't have anything to do with the electrical work you just did? You were messing around up front near the parking lights with the fan install. I know it's unlikely, but just seems too coincidental.

 

I agree...I hate those problems that are not repeatable. 

I'm quite confident that I did NOT brake anything wiring wise when  I was installing fans. I cannot, however, speak for what effect the fans have on the electrical system. Like I mentioned before, I did not notice a whole lot more load on the system, gauging by the dash volt meter.  The only thing right now that is questionable regarding the fan harness is the manual override wire which suppose to be connected to manual switch that is in turn connected to 12 V low amperage signal. At this point the wire is sitting coiled together in the engine bay. There is a possibility that the wire might have touched the body of the car effectively grounding it. I have hard time believing that this would create the issue, since the wire goes back to the fans relay. 

 

I'm still planning to look at all the other lights connected to that harness.

[Captain Obvious]

Regarding the override wire shorting to ground in the engine bay, I don't think that would cause the issue you had, but it could be a problem.

 

If you've got it wired as shown in the instruction sheet and the ignition switch is on, when the temp switch closes, you've got +12 on the yellow wire. And since the yellow and greens are tied together at the module, you've got +12 on the green. Shorting the green to ground would be a connection to ground through the ignition and temp switches.

 

Also, a little unrelated, but just noticed that they have a diode on the override wire. I'd put it on the one coming from the ignition switch instead. The way they have it, you can't back power the override source from the ignition, but I think it would be more important to make sure that you can't back power the ignition from the override source. Especially if the override source is hot at all times. Did I say that right?  Does that make sense? 

[Captain Obvious]

Considering how hot the fuse burned down, is it possible that the shortage took place somewhere else down the harness other than fuse itself? I was expecting to find melted wire at least in the vicinity of that fuse.

 

And yes, it's completely conceivable that whatever shorted was far from the fuse block. For brief periods of time, copper wires can carry an enormous amount of current. Even the smaller ones.

[Marios280Z]

Regarding the override wire shorting to ground in the engine bay, I don't think that would cause the issue you had, but it could be a problem.

 

If you've got it wired as shown in the instruction sheet and the ignition switch is on, when the temp switch closes, you've got +12 on the yellow wire. And since the yellow and greens are tied together at the module, you've got +12 on the green. Shorting the green to ground would be a connection to ground through the ignition and temp switches.

 

 Wouldn't the diode on the green wire (override) prevent from grounding path?

 

 

Also, a little unrelated, but just noticed that they have a diode on the override wire. I'd put it on the one coming from the ignition switch instead. The way they have it, you can't back power the override source from the ignition, but I think it would be more important to make sure that you can't back power the ignition from the override source. Especially if the override source is hot at all times. Did I say that right?  Does that make sense? 

 I think I got it. You recommend to put a diode, which is directional, on the yellow wire in a way that would allow flow from the temp sensor back to relay, but not the other way around, correct?

[Captain Obvious]

Yes, if you've got the diode on the green, then it should protect against a grounding path. That's not what it's for, but it will do that as well.

 

Actually the best thing would be to have diodes on both wires feeding that relay. Diode OR them together such that either of them could feed the relay without affecting the other.

 

 

[Zed Head]

I wonder if a bad fuse alone could cause the melting and self-destruction.  No short involved, just the fuse developing resistance at a bad junction and building heat from normal current flow.  Might be searching for a phantom.