"BD" wrote;
j>ury is still out, but will there be a certain number of miles before
Well, my two cents worth. Grounding kits and extra grounding wiring should be done only as follows; The negative battery cable should connect from the battery to engine block at a point where a solid and strong conductive connection can be made. Be sure the connection point for the neg. cable is clean of dirt, oil, oxidation, rust, etc. Use a star washer to improve the number of points the cable makes a good connection to the block. It can't hurt to finish the connection with a coating of something to prevent rust or other oxidation. The negative cable should never ground to the body and then the body ground to the engine even if it came that way from the factory.
The important part! The grounding kit should connect from this grounding point to any and all other grounding points you wish to reinforce with the grounding kit. In other words, the best scenario is to connect all your grounding wires from the point where the negative cable connects to the engine block to each of the other grounding points.
Of course, in real life, you may need to run a heavy battery cable sized wire from the negative battery cable grounding point on the block to a central grounding block kit connector in a more convenient location. But the point is that the kit should connect to the end of the negative battery cable at the block, not the battery.
You can connect one part of the engine to another part of the engine such as the block to the head, or the head to the manifold, directly with a grounding wire, since the manufacturer expects an electrical conductivity to exist through the bolts that hold them together. If it fails, the likelyhood of a fire or damage to elect. components is minimal, but does exist.
But as said by a poster, I would not count on a good internal conductivity especially after enough time for oxidation to occur has passed.
RF interferance is an interesting consideration in todays cars as pointed out by another poster. At a minimum, be sure items most likely to cause RF such as spark plug wires and charging system are in good condition.
Don't remove any shields which may seem unnecessay and in the way as they might be designed to reduce RF.
Always use very heavy guage wires for grounding kits. This is not only as a safeguard which gives a little extra protection handling heavier amperage to guard against fire but also something which the electronics guys may be able to explain, I can't. As they tried to explain it to me, heavier wire draws to ground a wider spectrum of interferance signals regardless of the source of the interferance.
As for the reduction of effect over time, I suspect that may be about not preparing the connection points well enough when installing the kits. Rust and other oxidation, loosening screws and etc. may be the culprits, I am not sure what 'they' are talking about. I know I hate preparing for connections like that by cleaning, sanding, recoating or repainting, etc.
Do not connect to the head or any other "bolt on" part of the engine. Ideally, even though the manufacturer does not do this, the negative cable should connect to the body of the starter motor itself to handle the 'cranking amperage' or 'cranking current', which can be extremely high.
Like the eletronics guy said, if the cranking current cannot complete its circuit through the negative cable, it will try to find any other path available including smaller wires you may have added as a "grounding kit" or other wires which already exist in the wiring chassis such as radio, heater, ECU, sensors, alternator and/or regulator, etc.
This can cause severe damage to any of these components.
If you run higher amperage through a wire than the wire can handle, it will heat up and burn off its insullation. This may cause shorting with other wires or a fire as insulation can burn as well as other flamable items like plastic parts and interior.
Ole Factory Rep (not Subaru)