Maintenance Q&A
Tire monitors and iced-up door locks

By Paul Abelson, senior technical editor

Q. I used to drive OTR, but for family reasons I wanted to stay close to home. I got a used Mack 10-wheel dump truck about a year ago, and now I do local construction and excavation work. I read a lot in Land Line about tire pressure and how important it is for fuel economy so I got a set of tire monitors. There’s one on each wheel and a readout on my dash.

These worked fine and let me know what my pressures are, so when my tires got low I could top them off.

I was in a pit one day and heard a bang. A chunk of concrete with rebar (reinforcing steel rods or bars) in it tore up my front inside drive tire. I limped to the tire dealer. I figured with seven out of eight drive tires I’d be safe running empty for 25 miles at city street speed.

They dismounted the blown tire. It was beyond repair, torn right through the sidewall. They suggested they inspect the tire next to it to see if it was damaged from running to the dealer.

The tire was OK, but both tire pressure monitors were busted. They were on the back side of the valve, so I guess they’re in a danger area if you get a blowout. 

I understand the inner tire monitor, but I can’t figure why the outer monitor broke when the tire was OK. The dealer said he’s seen lots of broken monitors.

Is there a widespread problem? Should I check the other eight before trusting any of them? Can you help shed light on this?

A. It is possible that you got a defective set of monitors, but I doubt it. Most tire pressure monitoring systems are designed in similar ways. They have a plastic box that houses an air pressure sensor and a short-distance radio transmitter. In some cases, there’s a temperature sensor, too.

The box attaches to the valve stem or is strapped into the well of the wheel. Those on the valve stem are either in a cap that threads onto the valve stem or are attached to the base inside the wheel. The boxes inside extend far enough into the wheels to obstruct tire tools used to mount or dismount tires. In fact, many installation manuals for TPMS units include warnings.

Tire irons need to sweep about 270 to 280 degrees, or roughly 3/4 of the way around a tire for mounting or dismounting. The service supplier should note the location of the valve assembly. When dismounting, the tire tool should break the bead at least 10 to 15 degrees past the valve. That way, it will have the tire loosened from the rim before approaching the valve assembly. That protects the TPMS unit from physical damage. The same procedure should be followed when mounting a replacement tire.

What leads me to think the tire shop damaged both wheels’ monitoring units is that both inner and outer units were physically broken, yet the outer one had not registered a warning on the in-cab monitor when you limped in, while the inner one did for the damaged tire. It was not broken when you came in.

If you have a tire pressure monitoring system on your truck, regardless of type, be sure to point that out before you have any tire work done. Inform the worker to be careful of the valve assembly. You might even want to write it on the repair order, to get it on the record in case there is damage.

Q. I had a problem with my 2005 Peterbilt’s door locks last winter. They were sticking, almost like they were packed with ice. When it warmed up in the spring, the problem went away and I forgot about it. Now that the cold is back, they’ve started sticking again. I regularly use lock oil, but now I’m afraid to. What do you recommend?

A. Living in the Chicago area, we have cold weather problems, too. In fact, I had this same problem a few years ago when the winters here were colder. Of course, keyless pushbutton entry solves most of these problems, but not that many trucks have it yet, especially older ones. A local locksmith gave me a few tips back then. I think I remember most of them.

There are a number of products on the market, mostly with alcohol or light oil bases. The alcohol fluids are primarily de-icers. When water drips or splashes into the keyholes, it seeps past the spring-loaded weather doors. Over time, the springs weaken and allow water in. When temperatures drop below 32 degrees, water turns to ice that can lock the mechanism solid. It’s often so bad, you can’t get the key into the lock.

Alcohol sprays can be squirted into the locks to melt the ice. If the situation is severe, you can heat the key with a butane lighter and slowly force it in. Its heat will melt the ice. Alcohol treats the situation, but does not prevent it. For that, you need a good lubricant and corrosion preventive to block the entry of road salts and snow removal chemicals that attack everything on a truck.

Some of the best lubricants for door locks contain graphite or PTFE (Teflon) either in dry powder form or with the powder suspended in oil. It’s thick oil that causes problems. It sounds as if you used a graphite-in-oil lock lubricant. The graphite makes the oil paste-like, and cold thickens it and eventually turns it solid.

You need to flush your locks with a de-icer. Use enough to flush out any residue. That will leave the locks without protection. My locksmith recommended Tri-Flow, a very light oil containing PTFE. The oil evaporates after displacing any water in the lock. It’s thin and drains easily, so don’t be afraid to overuse it. I get mine at Grainger, but it’s widely available. LL