Bottom Line
Maintenance Q&A

Paul Abelson
technical editor

Question: Terry Johnson, OOIDA member from Hazleton, PA, wrote about his 1996 Volvo that was previously a fleet truck of C.R. England Co. It has 740,000 miles. It has a 10-speed direct drive transmission. “My question to you is that if I do decide to replace the transmission with a 13-speed transmission, will that hurt or help me in the power and the fuel mileage? I have been told both, that power and speed will increase but mileage will go down and vice versa. Who do I believe?”

Answer: The 2.85 rear end is designed for direct-drive transmissions. It’s the equivalent of a 3.96 gear with a 0.72 overdrive or a 3.43 with a 0.83 overdrive. A 13-speed with a 0.83 overdrive would be like having a 2.36 rear end with direct. A 0.74 would be worse, like a 2.11.

C.R. England company trucks are speed limited to 65 mph. My guess is that as an owner-operator, you are probably driving a bit faster than they did. That would account for having to do 1,800 rpm to go 70 mph. They drove 60 at about 1,550, or 65 at 1,670 rpm.

If you wanted to cruise at 70 in top (direct) gear, to reduce engine rpm, a 13-speed with a 0.83 reduction would bring you to about 1,500 rpm. With a 17-percent split for overdrive, you could drop to 56 mph at 1,200 rpm before having to split back to direct. That would work on hills. You would also have more gears to play with to get your hill climbing (grade ability) the way you want it.

I would hesitate to go to a 0.74 overdrive, often found on 13-speeds. You would cruise at 1,330 rpm at 70, but you’d have only 1,140 at 60 mph, so you’d have to drive in direct at lower speeds. You’ll have to go direct at 63 mph to keep rpm above 1,200. The fuel economy and drivability results you get will depend on the 13-speed you select. Direct drive will give you what you have now. A 0.83 should give you more flexibility, but you’ll be unhappy with a 0.74.

Question: David Reed Sr., member from Marshfield, MO, wants to know about oil filters. He asks, “How can I learn what the filtration level in microns is for my CAT filter? Since this is a bypass filter attached to a factory mount built on the engine, would it not be sufficient? What is meant by ‘replenishing additives?’ Is it just adding fresh oil or Lucas by draining enough oil to add new, and if so, how much is enough?”

Answer: Micron ratings can be misleading. A full rating will indicate both the size of particles being rated and the percentage of particles of that size being removed. A filter can be rated at 0.1 microns, but it will probably remove only 1 percent or 2 percent of the particles that size. Common practice is to rate filters at either the 50 percent or 90 percent level, and that should be specified in the literature. Some manufacturers are reluctant to give out ratings. Full-flow (single pass) filters are generally 90 percent or more efficient at 40 to as small as 25 microns. A micron is 1/1 millionth of a meter, or 0.000039 inches.

Bypass filters work on a different principal. While full-flow filters, which put the full output of the oil pump through a paper screen, are the first line of defense against damaging particles, bypass filters take only a small percentage of the oil out of the stream, sending it through a depth of filtering material much finer than the full-flow and returning it to the oil sump. The small volume bypasses the engine, thus the name.

Since ultra-fine filtration restricts flow, only a small percentage can be filtered without hurting engine lubrication. Since this is an ongoing process taking about 2 percent to 3 percent of the oil flowing through the oil pump, and since the engine pumps about 60 gallons a minute, from 1 to 2 gallons are filtered every minute. Within a half hour to an hour, virtually every drop of the engine’s oil has passed through the bypass filter at least once. Most of it makes several passes an hour.

The capability of a bypass filter depends on the structure of its filtering medium and its physical size. Compressed fiber media may filter to 3 microns or finer, but most are in the 5 micron and up range. Tensioned filter paper cylinders and cotton yarn can filter as fine as 1 or 2 microns. The larger the volume, the more capacity to hold contamination. Large containers add several gallons of oil to sump capacity and hold far more contamination than smaller, spin-on, factory-mounted bypass filters. Factory mounted spin-on bypass filters may allow you to extend drain intervals from 12,000 or 15,000 to 20,000 or 25,000 miles, while large canisters may allow 60,000 miles or more. Always use oil analysis to determine when to change if you are extending intervals.

As for replenishing additives, oil is a delicate balance of base stocks and various additives. You replenish additives every time you add makeup oil or, if you have a short interval bypass filter, every time you add oil to fill a new filter cartridge. There should never be a need to drain old oil to make room for new oil or oil additives. If your oil analysis tells you to change oil, change it. If it says you’re getting close to needing an oil change, don’t fool around trying to extend. Trust your analysis and get the oil changed. If your oil is OK, there’s no need to replenish additives other than with makeup oil.

If you use a good premium oil, you don’t need any oil supplement. If you use discount store oil, an oil supplement may help, but it’s less expensive to get a premium brand name oil and stick with it. Today’s CI-4 and CH-4 oils are so delicately balanced, the wrong additive can screw them up.

Question: Michael Briscoe, member from Jasper, AL, tells us he carries an air wrench, a spare brake chamber and a sack of lights and pigtails. His question is, can we do a story on “repairs that can be done by the owner or driver, if they have the tools?”

Answer: There are three factors that determine what repairs can be done by the owner or driver. First are the ability, the knowledge and experience of the individual. Second, as Michael pointed out, is the availability of tools and parts to do the job properly. An air wrench is a good tool to carry, but a torque wrench is a more important tool. There is a general tendency to overtorque with an air wrench, whether replacing a tire, a spring or a shock absorber. Be sure to protect the torque wrench from shock and vibration.

Other important tools are a screwdriver set (including some Torx drives), ratchet wrenches, and box and open-end combination wrenches. Electrical tools let you trace wiring problems and diagnose system failures. I carry a multimeter, terminals and crimping tools. I also keep a can of liquid electrical tape (vinyl to seal connectors), several sizes of heat-shrink tubing, and to prevent corrosion in sockets, Truck-Lite NYK dielectric grease.

The third consideration is legal. According to the Code of Federal Regulations, 49CFR Part 395.25, you cannot work on brakes unless you have formal training in an approved program, had one year as an apprentice or experience working on brakes working in a commercial garage, fleet leasing facility or similar operation. Unless you meet minimum qualifications, you can’t work on brakes.

Question: Tom Hartung, DeSoto, KS, has been OOIDA member since 1989. He has a 1995 Freightliner he bought new in 1994. He has 1,127,538 miles on his N-14 Cummins. He wrote, “I used to add about a half gallon of oil between changes (average 12,000 miles between oil changes), but now I am adding 1 to 2 gallons between changes ... I am not burning oil, nor do I have major leaks.

“Is it possible that the high engine temps on the hard pulls lower the viscosity of the oil to the point that it is seeping by the various gaskets due to their age? If so, can I help by using 11 gallons of Rotella and maybe one gallon of 40- or 50-weight oil at my oil change?”

Answer: To see how bad your oil problem is, I calculated that adding 2 gallons between changes, you are getting 6,000 miles per gallon of oil, or 1,500 miles per quart. This is really quite good for an engine with as much mileage as yours. Most experts consider 1 quart per 1,000 miles to be borderline excessive. I would just stay with the Rotella-T 15w-40 oil and check oil analysis to see if any wear metals, especially iron and chromium, are high.

Before mixing oils of different viscosities, I would do several things. The oil has to be going somewhere. If it isn’t visible on the side of the block or in the coolant, and there’s “only a small leak around the oil pan (which has never been off),” my guess is that the valve guides and rings are showing signs of more than 1 million miles of wear. The oil is probably being burned in minute amounts.

If you plan to keep the truck and engine for a while longer, you might consider having the engine overhauled in the near future. For now, your best course of action is to keep your oil topped up and see what the analysis says.

About a year ago, I wrote about a product I saw at the Great American Trucking Show. Airtabs (, 1-800-475-2155) are triangular aerodynamic devices about 3-inch by 3-inch by 1-inch high. Technically, they are vortex generators, designed to smooth air flow from the rear of a tractor, trailer or both, improving fuel economy, increasing stability and keeping the back of the vehicle cleaner.

I tried them on my van. While I can’t run a full SAE/TMC Fuel Economy Test, I can report that the Airtabs did reduce turbulence behind the van, and that in conditions that used to require running my rear wiper continually, I can now go long periods without using the wiper. The van also handles better with the devices. My conclusion is that Airtabs do, in fact, improve aerodynamics. That should lead to better fuel economy, by maybe a few percentage points. I think that’s worth sharing with you.

— by Paul Abelson, technical editor Paul Abelson can be reached at