Static and Dynamic Torque is like astronomy, the more you find out about it the more you realize what you don't know. Not sure if the Jeep Service Manual states dry un-lubed or if they convert to the environment you are torquing in. I would think they should adjust torque values as required like torquing connecting rod bolts should be in an oil environment as should be the oil filter cap. Torque specs are usually dry un-lubed or as received new with the manufacturer's light coating of whatever for corrosion resistance that doesn't affect the torque value. Motor oils in the 30 weight range are considered to affect torque by 20% and you should adjust for that and reduce the torque value by 20% if not already corrected.The wrench could be set at 18/ft lbs. However torque wrenches and torque values are stated for dry un-lubricated threads, because there is no way to accurately calculate all the different effects different lubes can have on thread. Yes the wrench will click off at 18' pounds but the actual torque will be a lot higher. Which translates to crushing the washer a lot more and the cap going deeper into the housing, stressing it more.