I've been chasing a burning plastic smell in my S10 LS swap. As I've removed possible sources, it has gotten better, but is still there. Which leads to this topic. I have a bulkhead connection on the passenger side of the engine bay, and the wiring runs less than an inch from one of the header tubes. That tube is wrapped, the wiring is in split loom tubing, then wrapped in reflective anti-heat tape. The reflective material hits about 260-270F on my IR thermometer when the engine is running, up to temp, and sitting still. I have no idea what this would translate to on the interior of the loom, but as it is in an area that doesn't get much air flow, I would assume it would still get pretty hot.
The smell (or at least some of it) is definitely coming from the back of the passenger side of the engine compartment. I have pulled the tape and loom off the wiring before, and it looked like it was not melting, but I'd assume the heat will eventually degrade the insulation anyway, and the insulation is likely the source of the smell.
I have been trying to find a place to relocate the connector too, but they will all require considerable work. Some of my fellow GRMers are going to take a look, and see if I missed something obvious, though.
Just wanting confirmation from the hive whether the wiring is the likely source of the smell, and is not a good thing for the wiring harness long term? Also, if you have any tips other than relocation that could fix the issue, I'd love to hear them. One thing I thought of was using some aluminum sheet as a barrier, but the gap is so small, I don't think I could guarantee it wouldn't eventually end up rubbing against the wiring, the header, or both.
wae
PowerDork
5/29/23 12:12 p.m.
I don't know if it would help, but I do have a thermometer that plugs in to my multimeter. We could wrap that up and see how hot it gets.
Most automotive wiring insulation is rated for around 200 degrees F.
There are temperature indicator dots that change color if exposed to a particular temperature - you could bury one in the harness and then unwrap it to see if you're hitting the limits.
Looking at a few different listings for split loom the max temp ratings are anywhere from 185F to 275F.
Sounds like it could be the problem. Didn't even think about the split loom itself, that could be the source of the smell. However, if it is getting too hot, then the wiring is probably getting too hot, too. I'll take a look at those temperature dots, but may unwrap the harness again before doing any ordering and see if anything looks worse than before.
wae, I keep forgetting, I am hoping at some point to borrow your oscilloscope to see if my speedometer signal is working, and it's the gauge cluster that has failed.
wae
PowerDork
5/29/23 1:25 p.m.
In reply to eastsideTim :
I haven't had time to check with my Operations Manager yet, but I should be able to break away some night this week if you want.
In reply to wae :
Cool, thanks! Plus, maybe you'll see a different place I can route these wires that I haven't noticed yet.
Another fun angle; wiring insulation is effectively derated inre: temperature when it's in a bundle vs. free air space. It can't shed heat as well if it's bunched up with other wiring. Unfortunately I don't think there's an easy rule of thumb on this but it's probably a 10% drop in heat rating (from memory). And it's dependant on the contents of the bundle.
Probably need to get that stuff rerouted.
