Alternator melted rubber terminal boot? (1 Viewer)

[pawnthatdude]

Hi all,

This weekend I started getting an occasional battery light on the dash that would come and go as I drove down the highway. I stopped and tested the battery and sure enough the alternator was basically not doing anything. I'd just replaced the alternator a few weeks ago with a rebuilt Toyota one, and I coated the terminal and boot with dielectric grease at the time. As a one bannana mechanic (on a good day) it all seemed fine to me when i installed it.

I took a look at the alternator terminal for the battery cable and the boot was ripped and the boot was filled with crusty white powder. This was causing an intermittent poor connection. I took the cable off and cleaned the surfaces and it's working now as normal. But why did this happen in the first place? And what was that powder? Dried up burnt dielectric grease? Corrosion? Magic alternator dust?

 

[pawnthatdude]

Bumping this. And maybe this picture will help. It's my alternator boot after I cleaned all the white crusty crap out under it.

 

[flintknapper]

High resistance. Replace the entire lead. Also check your grounds.

 

[ZackR]

As @flintknapper mentioned, the bad connection resulted in high resistance, which equals high heat. Swap out the cable, clean it up and you'll be in good shape.

 

[BILT4ME]

Realize that dielectric grease is designed to RESIST electrical flow.

If you places it between the connections and one of the connections did NOT have a serrated star washer, you essentially isolated the high voltage terminal from the wire.

You SHOULD bolt the connection together THEN apply the grease on the OUTSIDE of the completed connection to seal it from moisture.

On plug-in connections it works out OK because the blade terminals cut through the grease and make positive connection. On a flat terminal when you "pancake" the parts together, it will insulate one from another.

 

[pawnthatdude]

High resistance. Replace the entire lead. Also check your grounds.

As @flintknapper mentioned, the bad connection resulted in high resistance, which equals high heat. Swap out the cable, clean it up and you'll be in good shape.

Much appreciated. Do you know what gauge the cable is? It seems like 4AWG would be what you need for 80A and <15'. And how could I get a new boot?

Realize that dielectric grease is designed to RESIST electrical flow.

If you places it between the connections and one of the connections did NOT have a serrated star washer, you essentially isolated the high voltage terminal from the wire.

You SHOULD bolt the connection together THEN apply the grease on the OUTSIDE of the completed connection to seal it from moisture.

On plug-in connections it works out OK because the blade terminals cut through the grease and make positive connection. On a flat terminal when you "pancake" the parts together, it will insulate one from another.

I did apply the grease after bolting it together, but the terminal is not serrated and there was no washer as far as I saw.

 

[flintknapper]

Realize that dielectric grease is designed to RESIST electrical flow.

If you places it between the connections and one of the connections did NOT have a serrated star washer, you essentially isolated the high voltage terminal from the wire.

You SHOULD bolt the connection together THEN apply the grease on the OUTSIDE of the completed connection to seal it from moisture.

On plug-in connections it works out OK because the blade terminals cut through the grease and make positive connection. On a flat terminal when you "pancake" the parts together, it will insulate one from another.

^^^^^ Correct. Dielectric grease (NOT to be confused with conductive grease) is non-conductive and also an insulator. It is certainly possible (with loose connections) to create a situation where you impede the flow of current. The grease CAN be used between connections but only if the mechanical joining of the parts displaces the grease.