interesting heat related short

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hubertyb00

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hi, i am an electrician, but i work at an auto shop for now. I didn't know anywhere else to go, so i need to post this. Basically, whenever we left the car out in the sun to get nice and hot, the main fuse for the ignition blew. So, we put in two in-line fuses(one for fuel pump, and one for starter). We tried it and the fuse for the fuel pump blew. so, it had to be in the fuel pump circuit. we replace the pump, let it sit outside, and it happened again. Eventually, what we did to fix it was run a whole new wire to the pump and abandon the old one. This did fix the problem, which leads me to my question. I was just wondering, what would heat have to do with causing a higher than normal amperage in the wire? When it was inside, we didn't have the problem, only when out in the heat. i know this is an electrical site, but i thought that this was pretty interesting and wanted to know if anyone had any theories. I just cant think of an intermittant short that would only happen when it was hot.
 
my guess would be bad isulation that is barely touching ground and when it gets hot enough the metal expands shorts out the circuit and blows the fuse.
 
Heat will cause materials to expand and move so it's possible that the wire is pinched or rubbing at some point cutting through the wire insulation. This could also happen at a harness splice point within the harness where the splices weren't insulated as well as they should from each other.

I think if it were me I would have been curious enough to follow the wiring to see where the problem was.

-Hal
 
thanks guys for the thoughts. to be honest, i wanted to explore more too to find out why, but the customer needs their car back, u know. Anyway thanks again.
 
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