Has anyone had their coolant plug heater fuse box melt?

20ValveT

Veteran Member
Joined
Oct 4, 2002
Location
Canada
The coolant plug heater fuse box on my A3 TDI melted the other day. For those of you unfamiliar with this item. The coolant plug heaters are these plugs which help heat up the coolant when the engine is cold . The fuse is located on the drivers side of the firewall. I tested the voltage and the amps going through the box and it measured 39amps, VWs specs allow there to be a Max of 80amps to run through this box. The funny part about this is while the box was melting the fuse never blew. I replaced the positive wire connecting to the box and put a new fuse in, despite the box being melted on onew side it continues to function. Any thoughts?
 

MacGyver

Veteran Member
Joined
Mar 13, 2000
Location
SW Ont, Canada
TDI
1997 Jetta, black
Yup, happened in my 97, so I soldered the lug onto the wire, cleaned all connection points up, used an anti corrosion grease on all connections, replaced the fuse link with a new one for good measure, and no more problems. Mine is slightly melted too. Been fine over a year now


But, you won't need that fuse once you get your VR6 in anyway!
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H
The one in my red Passat melted away and never blew the fuse. Heat is produced at the point of greatest resistance. Normally that is the glow heaters in the coolant. If a short circuit is created, (with no resistance through the heaters and the current goung straight to ground), then the fuse is the greatest resistance. The fuse gets hot and melts cutting the current flow.
The screw holding the wire to the fuse on my red car was loose and made a poor contact. The resistance of the poor contact created heat at this point. The fuse was able to carry the current that made it through the bad contact, but the contact area itself became the highest resistance and the hottest point. The heat melted the plastic screw support. I pulled the fuse and drove for another year without heater core heat assist.
I've made certain that the one in this black Passat remains clean and tight. The heat assist helps, but isn't necessary.
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
This happened on my car (97 JIII), to the prior owner. I dont know what VW did to repair the situation but when you look under the hood the right corner of my clear plastic cover is melted and the dealer wrapped the wire in electrical tape to cover the insulation that had melted. The fuse link never melted. This situation scares me, I think I'll pull the connections at the heater plugs, clean them and put dielectric grease on them to make sure that they are contacting ok. I also dont like the connection at the link but dont have time right now to mess with it.

Also, the fuse itself is attached to the bracket with zip ties, I dont know if this is the way it should be or not but it looks like crappy work. Let me know if it's supposed to be bolted or attached better.

[ December 12, 2002, 22:22: Message edited by: Steve Addy ]
 

20ValveT

Veteran Member
Joined
Oct 4, 2002
Location
Canada
The box itself is supposed to mounted to the firewall with two button clips. you know the ones you have to push the centre in to get them out. They are very cheap from the dealer.
 

dzcad90

Rolex & gin
Joined
Mar 15, 1999
Location
Joliet, IL USA
TDI
Jetta - 97 (RIP), '03 (Sold), '09
97 Jetta, and it's melted and has been for a while. Seems to still work. It takes a little bit of doing to replace the fusable link though, it has to be bent a little to get in there though.
 

Diesel Dude

Veteran Member
Joined
Jul 8, 2000
Location
Alberta, Canada
TDI
Jetta, 1997, Dark Green
My 97 has the coolant relay box meltdown happening as well. A new one is $200+ Cnd, so I have not been in a rush to replace it. By the look of the responses this was certainly a problem in 97 Jettas and the Passats. I am wondering if the replacement would be an upgraded part?
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
I'd be interested in knowing too. This is something that can be found in the Etka I'm sure, unfortunately mine isn't up and running at the moment.

steve a
 
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