Heaters and tire size

December 2019/January 2020

Paul Abelson


Q: In December 2015, I bought an Espar heater for my 2014 Western Star. I got it used from an independent truck garage. I don’t know how old it was, but the guy said he serviced it, and it worked fine. He gave me a good price and a one-year warranty. It worked great until a few days ago, when it just stopped working. I went back, and he’s no longer in business, so I Googled Espar for help. I couldn’t find it. I found Webasto, Eberspaecher, Air Tronic and a few more, but no Espar. I love the heater when it works, but now it won’t. What can I do?

A: You actually did find your heater online. A while ago, Espar changed its name to the name of the parent company, Eberspaecher of Esslingen, Germany. That’s the name the heaters have been sold as all over the world except in North America. In the interest of full disclosure, I worked for Espar in the early 1980s before I started consulting and writing.

The air heaters work by continuously burning very small amounts of diesel fuel in a combustion chamber that draws outside air to the furnacelike assembly and blows the exhaust through a pipe outside the cab. The fuel is drawn through an in-line filter, atomized and ignited to burn in the combustion chamber. Cab air is blown over the chamber and the heated air goes back to the cab.

The system, which is common to most diesel-fired cab heaters, has two parts that need periodic replacement: the fuel filter and the igniter.

On very rare occasion, the specialized fuel pump goes out.

When troubleshooting any device that uses electricity, make sure all wires and cables leading to the unit are corrosion-free and solidly connected and the unit is receiving at least 11 volts. Corrosion in wires or on connectors could be a problem. Don’t forget to check the leads to the controls and the fuel pump.

Assuming the wiring is good, and the minimum voltage is there, change the in-line fuel filter. If you had the unit for four years without servicing it, the filter is probably blocked.Cab heaters use tiny amounts of fuel, burning it very efficiently.

They run up to 20 hours on a gallon of diesel. That’s about 6½ ounces an hour, a tenth of an ounce a minute. The pulse pump delivers a finely measured supply that must go through a very small hose or the pump will be overwhelmed by backpressure. If you must replace it, use the special fuel line from the manufacturer. Follow installation instructions to avoid any downward stretches in the line. They could create air bubbles that could interrupt precise fuel flow.

Once the heater is running, the atomized fuel forms a continuous flame front, almost like a jet engine. But to get the heater started, the fuel needs a source of ignition. This is a glow plug or igniter, like a spark plug in a car. Over time, igniters burn out and need replacement. I would suggest checking the wiring and protecting connectors with dielectric grease every year when you winterize. Replace the filter and igniter every year or two, to keep your heater operating reliably when you need it.

Q: I have a 2011 Cascadia and I’m looking to buy a good 2015 or 2016 truck to replace it.

I found one I really like with good specs, but I’m not sure about the tires.

The problem is, I’ve always been a fan of big rubber. I run 11R24.5 now and have for years. They last a long time and perform well. But this new truck has 285/75R22.5s. They will probably need to be replaced in about six months. I found another truck that has good specs, including 24.5s, but I don’t like the cab nearly as much. I gross out a lot more than I cube out because I haul a lot to retail store warehouses. My question is, should I get the truck with the tall tires because of my loads or will the smaller tires work for me when I’m at full gross?

A: You’ll be spending your time inside the cab, so its features will be important to you. As long as the tires support the truck, which 22.5s surely do, you’ll be OK. With the legal distribution of 12,000 pounds on the steers and 34,000 on each tandem, the 285/75R22.5s will support the truck with 105 PSI in the front and 80 PSI in each drive tire. If you followed the tire manufacturer’s load-inflation tables, your 24.5s were at 95 PSI in the steers and 70 PSI in your drives, so you’ll be giving up a bit of ride comfort with the higher pressures. Will it be enough to notice? I doubt it.

It’s not the tire that supports the truck. It’s the air inside it. With more air volume, you don’t need as much pressure.

That’s why smaller tires with less volume need higher pressures.

Since the truck you like will be needing new rubber soon, you can keep your 22.5 wheels and go to the next size up, 295/80R22.5. They’ll let you drop steer tire air pressure to 90 PSI so you’ll feel less road shock through the steering wheel. You’ll also get slightly more tire life, but not as much as with the 24.5s. Offsetting this is that the tires weigh less and cost less, and the federal tax on tires is based on tire weight so that, too, will be less.

Whenever you change tire sizes, make sure to reprogram the drive for your speedometer and odometer. Revolutions per mile differ, so you don’t want to think you’re cruising at 68 when you get nailed for going over 70 or you think you’re making time at 68 when you’re actually going slower. LL


Paul Abelson, senior technical consultant, is a longtime contributor to Land Line. He’s a member of the Society of Automotive Engineers and a member of the Technology and Maintenance Council. In 1995, TMC awarded him its Silver Spark Plug award. In 2006, he received the Lifetime Achievement Award from the Truck Writers of North America. Although he’s “retired,” he still makes a popular contribution to Land Line readers with “Maintenance Q and A.”