Bottom Line
Maintenance Q&A

By Paul Abelson
senior technical editor


Q: I have a 2000 Kenworth with a Detroit Series 60. I run heavy haul. I ran regular green coolant but had electrolysis problems.
I rebuilt the engine two years ago and put in Detroit’s long-life coolant. Last week I checked and found I was two gallons low on coolant. I checked and there were no leaks.
My Kenworth dealer no longer carries Detroit products, and he tried to sell me Caterpillar’s long-life coolant. Can I use it with the Detroit coolant in the engine?

A: The quick answer is yes. You can mix brands of extended-life coolant, just as you can mix brands of regular coolant. You should premix coolant and deionized water before adding them to the radiator.

Don’t mix regular green coolant with red extended-life coolant. While the extended-life organic acid technology coolant mix can tolerate at least 10 to 15 percent dilution, adding much more will affect its long-life properties. Instead of adding green coolant, if you cannot find extended-life coolant on the road, top off with deionized water and adjust later. Or better yet, keep a jug of premixed extended-life coolant with you.

When we spoke, we discussed why you may have found yourself down two gallons. At the Technology & Maintenance Council we have a meeting every two years about failure analysis. We’re taught to go past fixing the problem and fix what caused the problem.

You mentioned you found a residue near the coolant overflow vent. That leads me to believe that you’re blowing coolant past the radiator cap and out the vent. If the cap doesn’t hold pressure because of a weak spring or damaged seal, coolant will boil prematurely and blow out. Each pound of pressure raises the boiling point 3 degrees, so a 15 psi cap raises the boiling point 45 degrees. Radiator caps are notoriously defective, usually with weak springs.

When doing radiator or coolant work, pressure-test the cap. If you need a new cap, pressure-test it before you leave the dealer. A surprising number of new caps are either defective or counterfeit.

Counterfeit parts are sold to dealers with the intent to deceive. They look like original parts, but are often made with defective materials or to improper tolerances and sold at lower prices. Your dealer may innocently think he is passing along a bargain, or a parts clerk may be getting kickbacks. Be wary of extraordinarily low prices.


Q: I’m having air-pressure problems. My truck wouldn’t build air, so the mechanic replaced my air governor and got it to build air. Now it is slow to build air again, and sometimes it quits building altogether. If I kill the engine and restart, then it will start building again. What could be the problem?

A: Because the problem was fixed, at least temporarily, when the governor was replaced, the mechanic found the immediate cause: Something was affecting the air governor. Here, too, practicing failure analysis instead of just replacing a component might have prevented the recurrence. So what was making the governor go bad?

When we spoke, you mentioned you never changed the air dryer cartridge. Air dryers are filled with tiny pellets called desiccant. When air is compressed, the level of moisture increases and has to be removed. The most effective way is by using desiccant pellets in the cartridge. They draw and hold moisture on their surfaces. When the governor unloads the compressor, some air is blown across the pellets, removing water and regenerating the cartridge. Thousands of the tiny pellets maximize the surface area inside each cartridge.

Air compressors have moving parts that must be lubricated. Over time, small amounts of oil get past seals and rings and into the compressed air. The oil flows through the dryer where it coats the pellets. Unlike water, the oil does not blow off. It contaminates the desiccant surface.

The oil also builds up in the governor and on air valves and could form gum or sludge that causes sticking. Contaminating the pellets is a slow process, but cartridges do need to be replaced periodically. Some makers recommend doing it annually; others recommend every two years.

Because replacing the governor was only a temporary solution, I recommend working backward. Replace the desiccant cartridge and check the compressor. Seals may be letting in excess oil, which could be affecting everything between the compressor and governor.


Q: The ABS warning light on my 2003 Western Star comes on every time I start it. My dealer inspected all the brakes. The sensors are fine. The front shoes needed to be replaced, but everything else checked out. Even after the fronts were changed, the light is still lit. What’s wrong?

A: When your tech checked the sensors, I’d guess he pulled them and bench tested them. At the TMC meeting, several attendees reported corrosion-caused ABS failures. Your truck has seen five winters, operating on chemical-coated roads. Your dealer should pull the hubs and examine the tone rings at each wheel end. Sensors read the rate at which the teeth (flats) of the tone rings pass under the sensors. They send signals to the ABS computer, which determines whether wheels are turning at the relative speeds they are supposed to.

When only one wheel slows down, it signals an ABS event. When teeth in a tone ring are corroded away, the sensors get signals equivalent to an event. If the signals are irregular, the computer senses and signals a malfunction. Corrosion at the tone ring could be an early signal of corrosion inside the wheel end at the bearings. Examine and readjust bearings as needed. LL


Paul Abelson can be reached at