Wet Torque vs Dry Torque

[Brian R.]

The issue of wet torque (lubricated threads) vs. dry torque on common fasteners such as lug nuts has come up in another thread and I will bring it to everyone's attention here. I will copy this thread into a more general technical forum (link) so that they will have input also.

What is everyone's experience with this issue? It is common knowledge that the torque value expressed in Service Manuals are dry torques. There are many exceptions to this generalization. For example, all bolts tightened into aluminum threads should be coated with anti-seize compound (at least I hope this is a good generalization). Also, critical fasteners such as rod cap nuts and main bearing cap bolts are always lubricated with engine oil.

Lubricating fastener threads is common under critical use conditions as described above. Why would automakers create manuals using dry torque as the standard when no lubrication is specified? It requires a lot of effort to remove thread contamination to the point that the threads are in new condition. Even so, this cleaning does not help with lubricant that is in the bolt hole. No one ever cleans out bolt holes under normal service conditions. Solvent treatment of bolts and blowing the residual solvent off with air is barely adequate. I doubt in general that mechanics go to the trouble of using new bolts or cleaning the used bolts well.

The use of dry torque makes no sense to me except under conditions of original manufacture of the engine. Even then, wet torque gives more even tightening pressure since it reduces the variability of the surface condition of used fasteners and holes.

I was taught to always lube bolts with either antiseize compound for aluminum holes, or engine oil for steel holes or nuts. This would give some over-tightening if the torque values are specified as dry torques for steel holes/nuts.

Does this extra torque really matter? Isn't an evenly applied torque more important to sealing and preventing warpage than absolute torque? I have never had a part fail from over-torquing using lubricated threads.

Opinions please....

[Soilent Green]

I had never thought about that. Makes me want to check on some fasteners I wet-torqued to factory specs to see if they need retorquing...

I agree that it makes no sense to dry-torque a bolt that was kind of hard to remove...

[jdmccright]

I've been wanting to toss in one of my 2 cents in the tech forum but haven't had the time yet. But I'll agree that an even application of torque is most important for multiple-bolt sealing applications such as camshaft covers and manifolds.

Where torque is needed for correct bolt preload is where the proper method should be used...dry or wet. Which one? I've no clue since I don't write the torque specs but I do know that if a repair instruction specifies using a lube, use it. If it doesn't, don't. You shouldn't lube a bolt just to make it easier to remove later (except for bolts into aluminum...I'll agree there). Part of the bolt's holding power is the friction between the threads that keeps the bolt from backing out.

I'll give my other cent when I get more time...