Bottom Line
Maintenance Q&A

Paul Abelson
technical editor

Question: I have a question about temperature and tire pressure.

You always read or hear that you must check tire pressure often. But say it is 70 degrees out and I put all my tires at 95 pounds per square inch. Then the next morning it is only 40 degrees. My tires will be down to 85 to 90 psi. Should I put them back up to 95, knowing the temp will increase throughout the day?

I have also noticed that when I am checking my tires first thing in the morning and the sun is shining bright on one side of the truck, the tires that are in sunlight will be 2 to 3 pounds higher than the other tires. Should I make them the same as the other tires?

Answer: I checked with some friends from The Technology and Maintenance Council who happen to be among the leading authorities on tires in the country. Guy Walenga is from Bridgestone/Firestone, and Peggy Fisher, former president of Roadway Tire Corp., is a nationally known consultant and writer. Both have been awarded Silver Spark Plugs for their contributions to our industry.

Here’s how Peggy summed it up: “Cold tire pressure is technically taken at 70 degrees F. Therefore if the normal temperatures are around 70 degrees during the day, the reader should leave his pressures alone if they are all less than 95 in the morning when the temperature is 40 degrees.

“However if one tire is significantly less than the others, then that tire probably has a problem. Tires that are in the sun will experience increases in their pressure. Ignore these increases as they will even out as the vehicle changes direction en route.”

Guy put it this way: “If all the tires are set when it is 70 degrees ambient, yes: At 40 degrees, the air contracts, and psi may drop about 1 psi per 10 degrees. So, if the tires we are talking about at 95 are drive and trailer tires, they are already overinflated to carry a max load by nearly 20 psi (better overinflate than underinflate). If they drop by 3 psi, not a big deal. This is about the error range in most gauges, and all the tires are dropping the same.

“When tires are warmed up during use, psi is about 10 psi higher than cold. In the reader’s example, he is checking some in the sunlight and others in the shade, but in the morning. Here, the 2 or 3 psi difference between sun and shade is again too small to worry about.”

He goes on to say: “Steer tires should be inflated to carry the max load always. Check these often. There is no room for error.

“All the other tires on a drive and trailer are inflated for load but are almost always overinflated to make maintenance easier. The real issue is to keep the psi even between mated duals, keeping differences to less than 5 psi between duals. So you can see that a few degrees in temperature is not too big an issue and is made less an issue by good, consistent, psi maintenance practices.”

Our compliments for gauging your tires instead of just thumping them. You’ll benefit with better fuel mileage and longer tire life.

Another place to check
On the Internet, a driver was kind enough to share his experience. Instead of a question, he offered an answer that all Cummins owners might benefit from.

“This is something I accidentally stumbled across and thought I would share my experience.

“When I bought my Western Star last June, it had good power, but that seem to be declining after about a month or two. Last week I decided to fix my little problem (by looking at the fuel system) going back into the tanks. Whenever I tried to drain water out of my filter or (when I) changed the filter (I would check or replace) the check valve.

“Cummins sold me a check valve and showed me where it should be located (on the plate where the ECM is located). Of course they sold me the wrong valve (they told me it was a 90 [degree] when I actually needed a straight). I’d never even seen one before so all this was new to me.

“When I removed the original check valve, I found it clogged with trash! I found a piece of flat plastic about the size of an eraser head of a pencil and something else about 1/4-inch long, 1/8-inch thick. The valve was jammed/restricted from movement either way.

“While we were trying to remove the trash, the valve came apart (this is a good thing). The bullnose just slips in the fitting with an O ring, spring, then valve ... The trash fell out. I wiped it out clean, reassembled it and reinstalled everything. And baby, let me tell you something ... The Star car is back!

“I no sooner got it on the road when I could hear the difference in the turbo, feel the difference in the acceleration. The power is great, and the best thing is that it even idles smoother. When I turn the engine over, it starts as soon as it turns over instead of turning over for 5 to 10 seconds before it starts.

“I’ve had the truck in the shop on the dyno and computer, and everything showed good. Fuel pressure was good, HP and blow by were well within parameters, but something just wasn’t right. It just didn’t seem to want to pull beyond 1,600 rpm (peak horsepower).

“This small little thing has made the biggest difference. So if you find after replacing fuel filters and adding injector cleaners that the motor just doesn’t seem right ... Check the ‘check valve,’ as it just might be clogged with debris restricting fuel flow.”

“The purpose of a CB is to communicate and to learn. You really don’t need to reach out more than about 10 miles under most circumstances, and even that is a lot. With all the other traffic, even five miles, or about five minutes, is adequate. If you get a Smokey Report, the chances are that by the time you get there, the officer will be long gone. Five to ten miles should be ample warning for accidents, traffic and weather conditions.

“I agree that one button access to weather radio is an important feature. The more weather channels, the better.

“The obvious exception to the 10-mile range is trucking across areas like West Texas or the Great Plains, especially at night. When traffic is few-and-far-between, range does matter. It rarely does east of the Mississippi.

“As several other posters wrote, the most important item is the antenna. Absolutely correct! A good one will make an inexpensive radio sound great, and a poor quality antenna will make the best radio sound terrible. With a good antenna, you can reach out farther, both to listen and to talk.

“The antenna must be tuned to the proper electrical length, using an SWR meter. Even the best antenna will make the radio sound bad if not properly tuned.

“Cable from the radio to the antenna is also critical. Inadequate size or poorly insulated cable, improper length cable and cable coiled on itself to save space will all affect sound. Some authorities say there should be 18 feet of antenna cable between the antenna and the radio. Coiled cable creates interference fields that cancel out energy to and from the radio. If possible, run the antenna cable around the cab (under the roof liner) rather than coiling it to get it out of the way.

“Professional installers know how to do this. Many CB shops located at or near truck stops do it right. Ask other drivers for a recommendation for a good one near you.

“Spend your money on a good antenna, a radio with features you will use, on quality cable and on a good installer. If you buy from a CB shop, you may get free installation.

“Don’t spend money on features you don’t need, especially the ‘cute’ beeps, dings, echoes and reverberations. Power mikes are fine if you need to reach out, but some drivers have them turned so high that the over-modulation makes their words unintelligible.

“If you want to converse rather than show-off, please don’t use the gimmicks. People who overdo it usually don’t have much to say, anyway.

“By the way, like anything electrical these days, protect all connections and exposed metal (other than stainless) from exposure to road salts. They are more corrosive now than they have ever been. Some of the brines the highway departments use will spray up to the full height of a truck.

“Truck-Lite’s NYK electrical grease is made to protect sockets and plugs exposed to the elements. Marine stores, some hardware stores and some truck stops sell “liquid electrical tape,” a brush-on vinyl protectant/insulator that helps keep out salt and spray. I get my supply from West Marine. They’re in many cities and on the Internet.”

Do you have a maintenance question?
You can write to Paul Abelson, technical editor, in care of Land Line Magazine, PO Box 1000, 1 NW OOIDA Drive, Grain Valley, MO 64029; or you can fax information to (630) 983-7678; or e-mail your question to truckwriter@netscape.net. Please mark your message Attention Maintenance Q&A. Although we won’t be able to publish an answer to all questions in Land Line, we will answer as many as possible.