Bottom Line
Maintenance Q&A
Fluid drains and contaminated coolant

By Paul Abelson
Senior technical editor


Q: I have a 2000 W900. Can you tell me how often I need to change my transmission drive axle fluids? Is there a way to tell when to change it other than mileage, or do you go by what is recommended? Speedco says 250,000 miles. I don’t know if I should trust them or not considering they might just want to make a sale.

A: Start by checking your owner’s manuals. They always provide service information specifically for your truck and its components.

If you are using conventional mineral oil, I would go with Speedco’s recommendation. 250,000 miles is good for 2000-era lube oils. If you got a fill with synthetic oil, you can easily go 500,000 miles.

While engine oils have to manage acids, soot and other combustion byproducts in addition to cooling, protecting from wear and controlling friction, transmission and axle lubes have a much simpler job. They cool, lubricate and suspend minute particles of metals worn from gears and other moving parts, and they protect gear teeth from extreme pressures, but they do not have to control soot or neutralize acids.

If you want to go longer on your transmission and axle lubes, siphon out 4-ounce samples for analysis. You can probably go a good deal further, but make sure there are enough extreme pressure additive, friction reducers and other key components left in it. If the analysis says the lube is still good, you can probably go another 50,000 miles or more. But I recommend that another analysis be done before then, about every 25,000 miles after 250,000 or 500,000 miles. Plot the results on graph paper and see what the trend is. You may be able to keep extending, but only if analysis tells you the fluids are still OK.

Q: I’ve been having a problem with my 1994 Freightliner. It has a Caterpillar 3406E that was overhauled by a Cat repair shop in October 2005. I had to take the truck back to the shop in December 2006 and October 2007.

Now, I’m about to take it back to the same shop again for the same reason. It has diesel in the coolant. This is the third time diesel got inside the radiator. Cat told me that they replaced injector cups and sleeves each time. It ran fine for about 10 to 14 months and then it happened again. The truck has never lost any power and does not smoke. What can I do?

A: This sounds similar to a problem another engine maker was having a few years ago. They changed the design and material of their injector cups, and the cups were being damaged by improper torque settings. The leakage from the cups wound up in the coolant, just like your situation. Harder steel could be more brittle, leading to fatigue cracks, especially if the cups were over-tightened.

But to be sure, I called Bruce Mallinson of Pittsburgh Power. He told me of a similar recurring problem one of his customers had. It was eventually traced to a cracked cylinder head because of overheating, so have your cylinder head checked for cracks.

A 180-degree thermostat will help the engine run cooler. Check with your Cat dealer to see if he has any service bulletins about cylinder heads or leaking injector cups. Since this is recurring, you may want to talk to the Cat regional service manager. You might also have a bad or cut O-ring. Although unlikely at a Cat dealer, you may have gotten counterfeit parts. Counterfeits are made of inferior materials or are dimensionally out of tolerance. Also, haste, carelessness or improper technique could lead to failure. LL


Paul Abelson can be reached at

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