# Overheating/Toasted Fuse - TT Summer Dayz



## asiwa (Dec 18, 2014)

Hey gents,

Hope everyone is doing well! I've got a curious electrical/overheating issue that may be commonplace, though I've never encountered anything like it before.

I had the great pleasure of my car overheating on me for real (as opposed to low coolant or a bad sensor) while driving on the PA Turnpike last weekend. I was in stop and go traffic and was suddenly greeted with an overheat alarm, so I pulled over and let the car cool down for a while. I checked 49C and the car was up around 120°...so definitely overheating.

Once the car had cooled down to around 104, I ran the motor to see if the fans would run as they should be by that temperature. No dice. My A/C doesn't work right now either, so I couldn't force the fans on by running the A/C. I assumed it was just a bad main fan, but then I opened up the battery fuse box and found this beautiful sight:










Now the last time I checked, fuses are supposed to blow when they short out. Instead, this guy just shorted and heated up until it completely melted the socket and charred the hell out of the fuse. When I went to pull it out, part of the left terminal tore off and got stuck in the socket. I recall these fuses being for the car's ABS and fans, though which ones are which I can't recall since it was so long ago.

Has anyone ever seen this before? The amount of damage there is disconcerting to me. I thought that my primary fan may have caused that if it went bad, but that seems sort of far-fetched. It was also raining quite a lot over here over the past couple weeks, so I assume some water could have infiltrated a fan connector, if that fuse actually controls the fans.

Any help is greatly appreciated! Summer is fast approaching and driving around like this gets stressful when I gave to sit in traffic  

On a lighter note, my TT turned 15 just last week!  I also managed to figure out the creaking noise on my car - both my front left ball joint and left sway bar link were bad, so thank you to all that offered advice!


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## Sniper911 (May 30, 2015)

I had the exact same thing happen to me last summer here in nj. I thought the same thing and was all set to swap in a new fan or fan control module. Turned out the fuse on top of the battery melted instead of blowing out. I dug it out and fixed the socket and put a new fuse In it and haven't had an issue since (so far) 


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## hunTTsvegas (Aug 27, 2012)

Pretty common. Some have completely replaced the fuse block with more durable components. Can't remember who at the moment but hopefully they'll chime in. 

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## YayItsBlake (Apr 11, 2016)

Painless wiring sells some pretty nice fuse/distro blocks. I'd gut what you have there and wire one of those in if you have to do anything more than fix a burnt socket. 

I've had a few fuses melt the socket rather then blow, and they usually melt the wiring a few inches back from the socket pretty substantially. Keep an eye out for bad spots when you fix it. 

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## asiwa (Dec 18, 2014)

Thanks for all the replies!


YayItsBlake said:


> Painless wiring sells some pretty nice fuse/distro blocks. I'd gut what you have there and wire one of those in if you have to do anything more than fix a burnt socket.
> 
> I've had a few fuses melt the socket rather then blow, and they usually melt the wiring a few inches back from the socket pretty substantially. Keep an eye out for bad spots when you fix it.
> 
> Sent from my LG-H811 using Tapatalk


Dang, really? I'm surprised at how common of a fault this is. Should I not be concerned about whatever caused this to short out in the first place? 

Regardless, I'll check out Painless wiring. I'm going to have to replace the entire block anyway so I may as well do it right. 

Thanks again everyone!


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## YayItsBlake (Apr 11, 2016)

I'd say replace all of the carnage with quality components, then if you're still popping the same fuse you'll obviously know there is an issue. Could be 50/50 as to whethere the old socket and fuse was the actual issue, or just a symptom, but at least this way you rule out the old stuff and it costs $.07 per fuse to diagnose any additional problems rather than melt the box. 

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## carsluTT (Dec 31, 2004)

The MK4/TT has a common problem of melting the fuse box on top of the battery there are a few things that can cause this:

The nuts holding the wires and fuses in place have come loose causing high resistance witch can cause heat and can melt the fuse box.

Alternator cable has over time created high resistance between the terminal and the cable at the fuse box witch can cause heat and melt the fuse box.

Cooling fans are going bad witch can cause high resistance and over heat the wires and fuse box.

Adding extras that require extra load on the fuse box can also cause overheating and melting of the fuse box.

I would always recommend that you find and fix the problem before it just happens again.

been an issue that i am dealing with on both my TT's..... my plan is moving away from the mk4 style rad fans as that is the source of my issue.


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## lite1979 (Sep 9, 2005)

Once you replace the fuse block and fuse, let us know how bad the fans are. I haven't had this happen to my TT, but I had the small fan go bad on my mkIV Golf. It was getting power and trying to turn, but it seized and made a little smoke when it tried to engage...

This also happened to my lawyer's mkIV new beetle (2.0).


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## QCOUPETT (Dec 21, 2012)

*When things get really bad with this*

Can cause a catastrophic fire. A TTer here in Dallas lost his car because of this. Keep an eye on this. I check/pull the fuses once a month for damage. My fans went out, could not see the damage until I pulled the fuses and shined a flashlight into the aperture. Replaced my fans, and the fuse box/tray so far so good.


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## asiwa (Dec 18, 2014)

QCOUPETT said:


> Can cause a catastrophic fire. A TTer here in Dallas lost his car because of this. Keep an eye on this. I check/pull the fuses once a month for damage. My fans went out, could not see the damage until I pulled the fuses and shined a flashlight into the aperture. Replaced my fans, and the fuse box/tray so far so good.


Uhh...well with that in mind I will definitely have to address this soon. For now I removed the (new) fuse completely to prevent it from happening again. I'll be testing my main fan this week to confirm that that is actually what went bad as opposed to something else. 

I really do appreciate all of the replies. Electrical is something I've heard a lot about on our cars, but have not really delved into with much depth until now. I'll be sure to give you guys an update when I get a chance to work on the car!


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## asiwa (Dec 18, 2014)

Hey guys. Since I replaced the fuse (not the actual box) my fans have been running normally, especially on hot days like today. 

I don't really know what I should do at this point. I can replace my main fan as a matter of course but if it's running normally now, what could have caused the melting of the fuse box in the first place? Is the fan going bad but intermittently? Is it just bad wiring?

Any help is much appreciated!

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## lite1979 (Sep 9, 2005)

Drive it! It could be a matter of high resistance in the fan motor, a poor connection at the fuse tray, or just having your A/C on all the time, putting more load on your fans.

There's a mkIV fan system walk-through where they point out a failure point in the OEM fans, but I can't remember what it was. It's on vortex, though.

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## carsluTT (Dec 31, 2004)

i am dealing with this........ looks like the fan is the issue, tested everything else. i happen to have a extra set of mk5 fans from another project......... planing to spend some time trying to get them setup in my mk4...... should be a forever fix!.... but painful im guessing to make fit..


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## iBorg (Aug 20, 2014)

Had sorta the same problem earlier this tear. Fuses appeared good but no AC and the fanes wouldn't kick on. I also had an electrical overheating smell. Ordered the relays under the battery. Before they came in, whatever was stuck released and everything appears to be normal. Is there a good way to test the fans?

Mike


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## GrampTT (Apr 10, 2015)

*HRC*

The cause of this condition is a loose connection. This causes a high resistance connection "HRC" which results in a voltage drop across the connection causing localized heating. This causes further loosing of the connection, arcing, oxidation and then a lot more heat and melting of the fuse holder or wire insulation. HRC is the number one cause a electrical fires. It cant't be detected any means other than visual inspection and doesn't effect the fuse. To check the fuse holder you could cut the fuse in half and insert a blade into the holder to feel for correct tension. Goggle high resistance electrical connection.


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## lite1979 (Sep 9, 2005)

Would you recommend dielectric grease?

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## GrampTT (Apr 10, 2015)

I would not recommend applying a dialectic grease directly to electrical contacts. As the name implies DG is an insulator therefore will not lmprove electrical connectivity. It will reduce oxidation but should not be used particularly on loose connections. A better solution might be a contact cleaner combined with a PPE lubricant such as MG super contact cleaner with PPE (MG-801B-P). Ensuring a solid mechanical connection would be essential.


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## lite1979 (Sep 9, 2005)

Thanks for the prompt reply! I honestly haven't used dielectrical grease since my Volvo days with the old Buss fuses, but I wanted to ask since some guys use it as a universal solution to electrical problems. I do keep contact cleaner handy, however.


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