Maintenance Q&A
Extended oil drains and spring cleaning

By Paul Abelson, senior technical editor

Q. 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?

A. 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.

Q. I had my ’06 Kenworth in for its safety inspection, and the mechanic told me I had a squeaky drive wheel bearing. He wanted to replace all four wheel ends for a huge amount of money. He said that it’s quicker and easier to replace the entire hub with a pre-assembled unit than it is to replace and properly set up new bearings. And it’s better to do all four wheel ends on the tandem because if one is going, the others will too.

I’ve done a fair amount of work on my own trucks over the years. My questions for you are: One, is he right about the wheel ends needing a great deal of setup or is he just trying to pad his bill? Two, is this something I can do myself?

A. Let me answer your second question first. Wheel end bearings are critical components of any truck whether in the steer, drive or trailer position. They affect handling, braking and safety. One of the leading causes of wheel loss, according to the Ontario Ministry of Transportation, is bearing failure. After a number of wheel-off crashes in the mid-1990s, the ministry has led research on the subject.

Before deciding, research “wheel bearing adjustment” on the Internet. The most comprehensive and concise document is Recommended Practice RP618A, Wheel Bearing Adjustment Procedures, from TMC. If you have a dial indicator and the specific installation tool for your wheel-end assembly, and you believe you have sufficient expertise to follow the procedures precisely, go ahead and do it yourself. If not, you can buy a set of pre-assembled wheel hubs and bolt them on. They do save time and come accurately set.

Before attempting any wheel end work, make sure your torque wrench is accurately calibrated.

When lubricating a new bearing, use the same oil as in the differential, not grease. Save the grease for steer or trailer axles.

I recommend changing all four wheel bearings or hubs together, especially since each trip to a shop involves downtime that cuts into revenue. Get it all done at once. You’ll be ahead in the end. LL