If It Ain’t Broke, Don’t Replace Part
Question: My Toyota garage service writer keeps telling me I should replace the fuel filter on my 1985 Cressida, saying it should be changed every 30,000 miles. I now have 55,000 miles and the car runs fine. The repair manual doesn’t even mention the fuel filter as an item to inspect, much less to replace at any time or mileage interval. The garage wants $80 to replace the filter. Is this really necessary?--W. E. F.
Answer: Tell the mechanic to forget it. The high cost is justified if you needed the filter, but in your case it would be an unnecessary expense and would not be helpful.
The repair manual doesn’t mention the filter, not because the company forgot about the fuel filter but because it did not intend for it to be routinely replaced. Unless the filter is clogged, there is no benefit to changing it.
The fuel system in your Cressida operates at 40 pounds per square inch, a fairly high pressure. The system uses a porous metal filter element that is quite unlike paper filter elements. The filter is mounted at the bottom left side of the engine, where it is difficult and time-consuming for a mechanic to reach. The filter costs the dealer more than $20.
With higher quality gasolines and your system’s high pressure, you can consider it a lifetime filter.
Q: I have a small four-wheel drive pickup truck with Bridgestone Desert Dueler Tires. The size is P225/75R15. A tire dealer recommended another size, LT235/75R15. My question is whether it is safe to change tire size from my original? What are these numbers?--P.
A: The difference in size, especially in terms of the tire’s diameter, is relative minor. But the two tires you have described are substantially different in load ratings. The P stands for a passenger rating, while the LT stands for light truck. The LT tire has much a much higher load rating, meaning it has a higher sidewall strength, among other things. If you intend to tow a trailer or heavy boat, you would want the LT tire.
The 225 and 235 numbers refer to the width of the tire, measured in millimeters. The 225 tires is about about 8.8 inches wide. The next number, 75, refers to the ratio of the tire height to its width, meaning it is 75% as high as it is wide. The R indicates it is a radial ply tire, in which the cord body runs side to side rather than diagonally around the tire. And finally, the 15 refers to the rim diameter in inches.
For some reason, the tire and auto industry has elected to go with a combination of metric and English measures. It is confusing, but it is repeated in many areas of your car. Engine size, for example, is often stated in liters, and the gasoline tank capacity is always stated in gallons.
Q: My oil pressure gauge on my 1985 Pontiac Grand Prix is driving me crazy. It runs from one extreme to another. It seems worse on long trips than short. Is there any easy fix to this problems?--W. J. B.
A: The most likely problem is with the oil pressure sending unit, a small sensor that screws into the engine block. If you can find the unit, it can be easily unscrewed and replaced with a new one.
