Maintenance Q&A
Tips on re-torquing lugs and pulling a good oil sample

By Paul Abelson, Senior technical consultant

I recently had new tires put on my trailer. I noticed on the receipt that it says to have the lug nuts re-torqued after 100 miles. Why?

Problems arise with wheel studs when either too much or too little torque is applied to the nut. If too little, there will not be enough force to hold things in place. Vibration will loosen the nut further, and the wheel will rub over the threads, enlarging and distorting the bolt holes. Eventually, the wheel will loosen, crack or both. Too little clamping force may show up as damaged threads on the stud.

When too much torque is applied, threads stretch the stud beyond its elastic limit. It can no longer spring back to clamp the parts together with sufficient force. In many cases, the stud permanently elongates, increasing the distance between threads while narrowing the stud’s diameter.

Elongation too slight to detect with the naked eye may be great enough to ruin the stud. It can be found several ways. The first is with a thread gauge. The gauge should sit evenly in the threads. You can also lay the suspect stud against a new one to see whether the threads match.

A straight edge will also show any distortion or elongation of the threads when laid across the highest points of the threads. If any threads don’t make contact, discard the stud. Another way is to run a nut down the stud. It should feel the same all along its path. Any binding or interference is a sign of distortion.

Final tightening should be done by hand with a torque wrench. Compressed air-powered impact wrenches are excellent for removing wheel nuts, but not for tightening them. The errors made with air wrenches are almost infinite, with most leading to over-torqued and stretched fasteners, and eventually to failures.

Air wrenches should be calibrated regularly, then set to a torque value below that needed to firmly secure wheels. They should only be used to snugup nuts. Final torque should always be applied by hand, using a recently calibrated, properly cared for torque wrench.

The notice to re-torque the lug nuts after 100 miles or so is precautionary for you – and the shop. It’s a step intended to catch any lugs that have wiggled loose and to identify whether any potential damage was weakening the stud. It’s also important to note that most shops do not consider this a “suggestion” and will not pay for any damages resulting from a wheel coming off if you neglected to have the lugs re-torqued. So do yourself a favor and follow their guidelines.

My oil analysis last month showed very high silicon. The shop changed my oil and all the filters, including the air cleaner. They said that silicon usually comes from dust through the air cleaner. The same thing happened again this month: high silicon in the analysis. They wanted to change the air cleaner again even though they changed it just last month. There has to be another reason – or they sold me a defective filter. How much damage will it do to my engine? What caused it?

Damaged air cleaners are most often the source of spikes in silicon readings. When we spoke on the phone, we reviewed several alternatives and procedures to check. You were wise to inspect the month-old air filter and the air intake system for physical damage. Since none was found, there had to be another source. You saved the cost of a new filter.

At the shop, you discovered an apprentice doing oil changes. Instead of following proper procedures, he opened the drain plug without first wiping the area clean. Then he took an already opened sample jar, immediately placed it in the stream of dirty oil, removed it and capped the jar. Dust and dirt likely contaminated the sample.

There are better alternatives to the drain plug method. If you choose that method, TMC Recommended Practice RP318C, Used Engine Oil Analysis, suggests you thoroughly clean the plug and the surrounding area. Use a sample jar provided by your analysis company. Open it after the oil starts to drain, and wait until at least 1 gallon of oil has drained. Then put the jar into the stream of oil and take your sample. Cap the jar immediately and wipe it dry.

Sampling oil as it drains is not the best system for pulling samples because it eliminates any possibility of saving the oil if the report comes back good-to-go.

One better method uses a hose and a suction pump. With the oil warm and the engine off, place the hose through the oil fill tube until it is in the oil sump. Make sure it is not on the bottom, resting on the oil pan. You could be sampling sludge instead of oil. Draw 3 or 4 ounces into the pump and transfer it to a clean sampling jar.

Another system uses a fitting that screws into an external tap to the oil gallery in the engine block. Oil is held in by a spring-loaded check valve. Draw a sample with the engine running. Attach a short length of plastic hose over the large end of a needle used to inflate footballs or basketballs. Press the needle end into the check valve. It will open the valve, and oil will flow through the hose and into your collection jar. Remember to keep all fittings clean.

A similar valve can be spliced into the hose between the block and a bypass filter. Be sure to locate it on the filter’s inlet side so you’re sampling working oil, not ultra-fine filtered oil.

These devices let you sample oil without having to drain it, so you can decide to extend your interval if the sample comes back good-to-go.

In all cases, clean all fittings before sampling. In your case, the high silicon was most likely from external dirt that got into the sample. If the silicon is high next month, call me and we’ll take it from there. LL

(Editor's note: When sending in questions for Maintenance Q&A, please include the make and model of your truck and your vehicle identification number (VIN) as well as your contact information. Paul Abelson tries to respond to every question, whether it's published or not. Send questions to TruckWriter@WowAccess.net)