Thermally shielding a cable

Question

I recently bought and installed a GPS device on my FZ8 motorcycle that included a mounting-power supply kit along with it, as shown here https://www8.garmin.com/manuals/webhelp/zumo396/EN-US/GUID-1F65DB35-B640-4EAB-8970-1DA173A5DF32.html The battery on my motorcycle is located under the front (driver) seat and this power supply needs to either be connected with a bypass on the headlight power supply cables or to be connected directly to the battery. (The actual setup I use is connecting this GPS supply over the battery with a cigarette lighter receptacle alternatively used for charging other devices with a USB charger. This setup prevents the GPS supply from draining the battery, etc.) The longest part of the supply cable is a black (about 3mm) cable that takes the 5V output from the supply (under my saddle) over the device mount on my handlebar, thus it needs to cross the front half of my bike. In order to keep it tidy and not exposed I decided to route this cable under my fuel tank so it will be exposed to hot air temperatures due to engine running (and maybe even touching the engine block from time to time). The engine oil reaches sometimes +100C so we can assume pretty high air temperature right above the engine block.

For the moment I have been able to slip the whole length of this cable over two heat shrink sleeves (one inside another) and for some time now after inspection I haven't noticed any damage or even shrinkage on these. Is the cable inside them well protected or is there another way of insulating it without extensively increasing its diameter?

Note: The front (exposed) end of these heat shrink sleeves near my handlebar is shrunk and taped properly to prevent rain water gathering between the cable and the sleeves.

Answer 1

My experience with heat-shrink sleeves: they need to get very hot in order to shrink. I use a cigarette lighter held roughly 2" below the sleeve to shrink them. This heat would burn your finger instantly. By comparison, motorcycle engines typically don't get this hot.

My conclusion: the air flowing around the engine block won't be hot enough to damage the cables or shrink the sleeves. The biggest danger would be if the cables were in contact with the engine block for a prolonged period of time. This could melt both the heat-shrink sleeve, and the plastic cable housing.

Recommendation: try finding some of this cable housing (shown below). I don't know what it is called, and I don't know if you will be able to find any which is thin enough for your application. The only place I have seen it used is to protect coolant hoses inside car engine bays. It is used in places where the rubber coolant hose might come in contact with the engine block. The housing does not melt, and you don't have to worry about it filling with water/dirt. It simply ensures there is always a small gap between the engine block and whatever is inside the housing.

Note: I have heard that hot cables experience some voltage loss (?). Can someone confirm this? Is this something kokobill should consider?