At Boeing, I learned that bolts should be lubricated before torquing them in order to ensure an accurate torque. I initially thought wouldn't the lubrication allow the bolt to unwind itself? Surprisingly, no.
Since then, on my car, I always put a bit of grease on a bolt beforehand. It keeps the water out, preventing the bolt from rusting itself together. It makes for an accurate torque. I've never had one unscrew itself, and I can always get the lug nuts off!
Of course, you still need to use lock washers. For critical bolts, use a cotter pin or a safety wire.
> lubricating the threads can cause over-tensioning of the bolt if you torque it to the (typically) unlubricated torque spec
This is correct. My main exposure to it was from the ASME's boiler and pressure vessel post construction code - ASME BPVC PCC-1 - which is entirely about bolted joint assembly and torquing procedures.
I grease all the threads on my bicycle ever since I had a bottom bracket seize into a frame and lost the frame. I have heard that you shouldn't grease lug nuts on a car, though. I'm not sure why, so take it with a a large pinch of salt. It might be simply because most people don't regularly check the torque on the nuts and in that case it's more desirable to have them seize than fail.
Many bolts have a lubed spec and a dry spec. The dry one is, of course, completely unreliable. If it is lubed and ain't turning smoothly, take it out and clean the threads. Or get a better grade of bolts.
Anecdotally, I've been using loctite C5A (copper anti-seize) on lug nuts for years without an issue. I also torque them to the manufacturer spec with a torque wrench twice a year (when I switch summer/winter tires).
I use hi temp wheel bearing grease for the lug nut lube, as it won't melt and run when hot. Don't want grease dripping on the brakes! The amount is also a tiny dab, half a drop is plenty. I don't use a torque wrench, just give em a hard twist, lower the tire to contact the ground, then twist them all again just to be sure.
If you live up north, every autumn take off every lug nut on every car wheel, and one at a time oil it and put it back on. You'll thank yourself when you're caught with a flat in freezing cold and howling winter winds.
Since then, on my car, I always put a bit of grease on a bolt beforehand. It keeps the water out, preventing the bolt from rusting itself together. It makes for an accurate torque. I've never had one unscrew itself, and I can always get the lug nuts off!
Of course, you still need to use lock washers. For critical bolts, use a cotter pin or a safety wire.