Bottom Line
Maintenance Q&A
Squeaky doors, wacky headlights

Paul Abelson
Senior Technical Editor

QuestionI had the oil cooler changed on my 2000 Cummins Signature 600. While the dealer had it out for its test drive a rod bearing went out. Are these related, or just coincidental?

Answer: There have been reports of No. 4 rod bearings failing after ISX and Signature oil coolers are changed. 

One Cummins dealer I spoke with said it was caused by gasket material getting into the oil gallery, where it blocks oil in the rod journal oil hole. 

The No. 4 cylinder seems to be where this happens. He advised removing the old gasket very carefully, then probing the oil holes with a pipe cleaner (the kind used for smoking pipes, not the ones in your plumbing) to remove all debris and keep the oil passage open.

QuestionMy doors started squeaking after 150,000 miles. I sprayed the hinges with WD-40, which worked for a while, but the squeaks come back. It also smells. Will something work longer?

Answer: First, I would check the reasons for the squeaks. Squeaking is the sound of metals rubbing against each other. Lubrication works for a while, but if worn hinges have changed door/frame alignment, possibly because of stress being put on the door during entry or exit, the hinges may need to be realigned or replaced. 

When lubricating hinges, I prefer white lithium grease. It comes in small tubes and in aerosol sprays, so it’s easy to apply. Best of all, it stays put.

QuestionHow do you determine what weight gear oil to use in the rears of my truck? The owner’s manual is not available, as I purchased the truck used and it is missing. I haul bulk liquids in 48 states and Canada, 99.9 percent on-highway use. My truck has 46,000-pound rears with 700,000 miles on them. I presently have 75w-90 synthetic in them and was considering switching to 85w-140 synthetic. The logic behind the switch, in my mind, is to put thicker oils in the rears because of the mileage, to help things stay together longer.

Answer: To find out how to determine what weight of gear oil to use in the gears of a truck, I would contact either a dealer service department for the make of the truck or the service department for the component manufacturer to find out what they recommend.

I assume that since you mentioned high mileage, you are approaching an oil change at 750,000 miles. Personally, I do not believe in going to thicker transmission and drive axle oil because of high mileage; in fact, 750,000 miles is not particularly high for a rear end. That is the warranty period when synthetic oils are used, and most trucks go well over 1 million miles without any rear end problems. 

Years ago, high-viscosity oil made sense in engines where liners, rings, valve guides and other wear parts would get scored over time because of soot, wear metals and acids. Thicker, heavier oils would minimize blow-by and oil flow into the cylinders. Oil wouldn’t need to be topped-off as frequently. 

Today’s synthetic oils have far better flow characteristics. But more importantly, drive gears and transmissions do not operate in the same high-soot, corrosive environment as engines. As long as the oil is approved for use in the rear end, I’d go with the lightest oil available. It takes less energy to pump lighter oil, so fuel economy will be better, perhaps as much as one-half percent to 1 percent. Today, every drop saved counts.

Question(This one is from the OOIDA Maintenance Forum online.) I have a 1999 Kenworth W900, and the headlights went wacky. The only way the dim lights work is if the brights are on too. If I turn off the brights, the dims go off too. I replaced the fuse and the switch, no good. Any suggestions?

Answer: As with all maintenance problems, approach this one systematically. There were quite a few good responses on the forum. Let’s put them in order of ease of execution, while minimizing any expenditure for parts. 

First, if these are replacement lamps, check to see whether they are the right specification in the right place. Make sure double filament bulbs are outside and that single filament high beams are on the inside. 

Then check that the right plugs have been used for each lamp. If that checks out, check wiring for continuity and grounding. If you use a pointed probe, touch it to the metal connectors. 

Do not, under any circumstances, poke a hole into any wiring insulation. That creates a pathway for corrosive liquid. If broken or corroded wires are found, replace them. If you need to splice wires, use butt-connectors and cover the connections with heat-shrink insulation. When plugging into lamp sockets, use a dielectric compound such as Truck-Lite NYK. 

If the problem isn’t wiring, check any relays for proper operation. It sounds as if the wires may have become crossed up. If the relays operate properly and wiring is good, it’s time to check the dimmer switch. That may well be the culprit, but with switches costing $80 on up, changing parts is the last thing you want to do. 

One poster suggested borrowing a known-to-be-good switch and testing it for operation before you remove your switch. If it works well, your switch must be changed. If not, you’ve saved the price of a switch. But if all the cheaper fixes don’t help, it probably is the switch. The reason for checking all else first is to avoid buying a new dimmer switch and then finding out that was not the problem.

Paul Abelson can be reached at

Maintenance questions?
You can write to Paul Abelson, senior technical editor, in care of Land Line Magazine, PO Box 1000, 1 NW OOIDA Drive, Grain Valley, MO 64029; or you can fax questions to (630) 983-7678; or e-mail them to 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.