Reduce torque if stud threads wet with penetrating oil?

[Number_35]

This is w.r.t. my friend's 2012 Chevy Sonic. We were doing a seasonal tire changeover yesterday. The lug nuts on the rear wheels were very tight, but did come off with some persuasion from my corded electric impact wrench. The threads were rusty, and I cleaned them up with a wire brush on my drill. Torqued them to 100 lb-ft per the owner's manual. So far so good.

However, we could not budge the lug nuts on the front wheels. (Well, of course we could have with a long enough piece of pipe slipped over the end of a breaker bar, but I was afraid of twisting off the studs.) I squirted them liberally with penetrating oil, and sent the spray can home with my friend. He did several more applications yesterday and this morning, and came over this afternoon to try again.

Got them all eventually, though on most of them I had to hammer away with the impact for quite a while.

But anyway, in every case the studs were wet with penetrating oil. I've read here many times that lubed threads call for 20% less torque - so I torqued the front-wheel lug nuts to only 80 lb-ft.

Did I do this right? Is it valid to consider penetrating oil a friction-reducing lubricant? When he comes back in a few days for me to retorque the lug nuts, should I bump them up to 100#?

Thanks!

 

[eljefino]

Were these open ended lug nuts or closed? With closed, there isn't much of a path for penetrating oil to take.

When you put the lugs back on, by hand, was the running torque negligible? If it wasn't, your lug studs are probably stretched, and the threads aren't meshing perfectly. This is dangerous because they're closer to failure.

Correct procedure would have been to wire brush the studs, wash with brake cleaner or a similar solvent, wipe dry.

"Lube or no lube" (or what lube) is a religion here.

 

[Chris142]

If you sprayed them off with brackleaner the oil will wash off and you can torque them to spec.

 

[Number_35]

Were these open ended lug nuts or closed? With closed, there isn't much of a path for penetrating oil to take.

When you put the lugs back on, by hand, was the running torque negligible? If it wasn't, your lug studs are probably stretched, and the threads aren't meshing perfectly. This is dangerous because they're closer to failure.

Correct procedure would have been to wire brush the studs, wash with brake cleaner or a similar solvent, wipe dry.

"Lube or no lube" (or what lube) is a religion here.

These were open, so the penetrating oil was able to migrate in.

Resistance while threading the lug nuts on was very low. (Phew!)

Yup, should have used brake cleaner ... lesson learned.

 

[Number_35]

If you sprayed them off with brackleaner the oil will wash off and you can torque them to spec.

Yup, that's what I'll do next time. So it goes.

 

[Hall]

Torque them to 100 ft/lbs. Don't overthink this. The torque spec given by the automaker will allow for a "range" anyway. It doesn't have to be dead-nuts on at 100. 95-105, 90-110, etc will be fine.

 

[Dave9]

I'd retorque to 100#, spray penetrant doesn't leave a thick enough film to adjust by 20% anyway. Better a "little" over the spec than having them come loose later.

 

[Blueshound]

Lug studs have a large margin for error built in. They hardly ever fail even under the worst treatment. You're good.