Q: What's a good material to protect sensor wires in an engine bay?

What about 1/2" EMT?  It's cheap and relatively lightweight.

We had 2 different incidents where the 12V from the kill switch to the car (fuse box and starter) intermittently shorted out (for various reasons). Since then, we enclosed all 12V wires that are not fused within heater hose:

https://www.oreillyauto.com/detail/b/fi … 31/4322518

Its temperature rating is only 257 Deg F, so its not as good as the silicone hose, but its only $1.50/foot as compared to $5/foot for the silicone. Its firm enough that it won't crush when zip-tied, and it therefore won't put any stress on the electrical conductors.

What I like about the heater hose is that it adds dielectric withstand against shorting, and its very easy to route along a twisty path. Steel EMT would obviously would not have any temperature issues, but doesn't offer any short circuit protection if the conductors became exposed. Plus routing the EMT is more involved relative to any bends required. I got the red color so its easy for everyone to identify which hose has the wiring inside.

You can also buy non-metallic electrical conduit, but its only good for about 140 Deg F. If you are not worried about high temp capability, this stuff is pretty cheap:

https://www.homedepot.com/p/AFC-Cable-S … /202286718

What is the failure mode you are trying to protect against? 
Impact, abrasion, or heat. 
Polypropylene loom is probably the best for abrasion and heat.  https://www.waytekwire.com/products/146 … ypropylene

If heat is less of a factor and you are worried about abrasion, use braided nylon sleeve.  https://www.waytekwire.com/products/146 … -Sleeving/

I will add that proper cable routing and securing it with clamps is just as important as the protective covering.

I agree that clamps will be crucial here as we don't want any cables sagging and getting caught up with the driveshaft that runs forward from the engine to the front diff.

In thinking about things further,  I think that heat is a higher priority issue than abrasian. Our skid plate should go underneath the driveshaft here so that should protect everything but the most determined rock from flying up past the driveshaft and nicking one of the wires.

Heat Shielding didn't seem to be super high on the Wildcat XX engineer's design list so I do believe things will get pretty hot in this "transmission tunnel" space. The coolant hoses also run forward and backwards from the rear/mid mounted Yamaha 3cyl engine towards the front mount radiator through the same space which will also add to the heat soak. Stock UTV class prevents us from relocating the radiator to behind the passenger compartment so we will have to keep those coolant lines in place.