OK. This is a first for me. I may get the chance to actually get two people mad at me in the same thread...
I've always run mine under the wire wheel, lubricated them to eliminate any false tension/reading on the torque wrench. Never had a problem but there is a first time for everything.
I totally agree that clean threads are essential to consistent torque. However, it is important to know that lubricating them can have a large effect on the clamp load for a given torque, which may have less than desirable consequences.
Thinking back again to that fastener presentation, I remember a slide that was pretty interesting. It said that for a given torqued fastener, approximately 50% of the torque was used to overcome friction under the bolt head, roughly 40% was used up in friction of the threads, leaving only about 10% to provide clamp load. (Threaded fasteners are actually pretty inefficient, if you think about it).
The friction on either the bolt head or threads will be significantly changed by adding (or not adding) lubricant. In the "with lube" scenario, this means that as less of the torque goes into overcoming friction, more goes into stretching the fastener, resulting in higher than anticipated clamp loads. For some joints, this may not be a problem. For critical ones, it may be a pretty big deal. Of course, determining which joint is critical, and which isn't, is not always very straightforward.
For this reason, most manufacturers or assembly guides will specify either wet (lubricated) or dry torque specifications. Some instructions even specify the type of lubricant to use on the fastener if the torque spec is "wet".
Fortunately, there is a lot of "over design" in older vehicles, so they are pretty tolerant. If something has been working successfully for someone for a long time, it probably will continue to. However, I think it is also good to know some of what is going on behind the scenes, just in case things go south.
I know that I was once totally guilty of this when it came to lug nuts. My dad always put a couple drops of oil on each stud before installing the lug nuts. Torque for these is typically specified as "dry", so for most of my formative years, I was probably over-torqueing my wheels. Even now, when I know better, I feel like his ghost is standing behind me with an oil can every time I rotate my tires.
Once again, please take the above in the spirit that it was given. I am not trying to criticize, just inform.
Best Regards...
p.s. Yes. I like to replace the manifold bolts, too. Most are pretty rusty, or beat up when they come out.
