Flush Or Fleece?
Q: I drive an '00 Chevy S-10 Extended Cab with the big V-6 and automatic transmission. The truck is my daily driver and I've owned it since new. It recently turned over 60,000 miles. About that same time, I had a brake job done on all four corners. While the shop was doing the brake job, the crew there suggested that I have the brake fluid flushed and replaced. I didn't agree to that, because it sounded like bill padding for such a new truck. Also, the brake fluid didn't look rusty or anything.

Now I'm having second thoughts. The brakes work fine, but I wanted to get an impartial opinion. Should I have my brake fluid changed, or is this a variation on having metric air installed in my tires?
Trevor Taylor, Honolulu

A: As fishy as it sounds, replacing brake fluid on a five-year-old truck isn't a bad idea. We think the shop was offering you an optional service that wasn't mandatory but still a good idea. This type of service falls into the difference between owners who religiously follow service recommendations (including all suggested and required procedures) and owners who just fix things when they break.

Flushing and replacing brake fluid used to be the kind of service one would do to an old truck that hadn't been used for many years. The brake service industry (which obviously has a financial interest along with safety concerns) recommends that modern trucks have brake fluid flushed and replaced every three to five years. The industry bases its recommendations on time rather than mileage. The shorter time limits are for trucks with ABS and those used for heavy-duty applications such as towing.

The modest cost of flushing brake fluid can help prevent expensive repairs to the ABS system. Modern brake systems are more likely to experience high temperatures than older trucks. A cycle of heating and cooling can produce condensation.

Water contamination lowers the boiling point of brake fluid. That can increase brake fluid vaporization under emergency braking situations. The various anti-oxidation additives in modern brake fluids can lose some of their effectiveness over time, which is another reason to flush and replace brake fluid. The fact that you live in a very humid region is another reason to flush your brake system.

Brake fluid is designed to absorb water, so any moisture in the system is spread throughout the system. This is a good thing up to the point where too much moisture accumulates. That's when the brake system should be flushed.

A topnotch brake system is one of your best proactive safety features, so we'd go along with the shop and have your truck flushed.

High Speed Anxiety
Q: I'm disappointed in the performance of my '93 GMC Sierra. It seems to be down on power at higher freeway speeds, say 65 mph and above. It doesn't run rough, but it just seems like it used to handle these speeds much more easily. My two-wheel-drive truck has the 5.7L V-8 and automatic transmission. The engine is completely stock and has about 97,000 miles on it. It hasn't ever had any major engine work done to it. I'm hoping you can supply me with some quick fix for my problem. Thank you.
Slade Neuscom, via e-mail

A: It sounds like you have a basic maintenance neglect problem. It should be pretty easy to fix. The most common sources of problems such as yours are either a lack of air or fuel or the ability to get rid of the spent air/fuel mixture (exhaust gases).

The easiest thing to check is the air intake path. An overly dirty or clogged air filter is a common culprit. While you're checking the air filter condition, inspect the path to the filter. Any debris or restriction in the airbox ducting will hamper airflow. If the air filter needs replacing (and it most likely does), consider upgrading with a high-performance filter such as those offered by K&N Filters.

A more likely source of your problem is some type of fuel-delivery problem. This isn't as easy to check as the air filter. An inline fuel filter that's ready for replacement can restrict fuel flow when demand is the highest (e.g. at high speeds).

Fuel filters are inexpensive, so it's a good idea to install a new one. Be careful and follow the instructions on relieving fuel pressure before disconnecting the filter. Be sure the new filter has its arrow pointing in the right direction.

If replacing the two filters doesn't solve your problem, the next place to look would be the internal gas tank fuel pump pre-filter. It can get clogged with sediment. You could also have a fuel pump that is underperforming. You can test the fuel pump at home, but we'd suggest letting a repair shop do the testing.

If the air and fuel components check out, the next place to look is the exhaust system. Do a simple visual check for any crushed or restricted sections of the exhaust pipe. It's possible that your catalytic converter is failing. A basic home test is to tap the converter with a rubber mallet when the converter is cold. If you hear rattling, have the converter thoroughly checked at a muffler shop. A muffler shop can also check the converter with a pressure gauge hooked up to the exhaust system.

If your catalytic converter is going bad, you may have noticed some other symptoms. A loss of high-speed power is the most noticeable sign of a bad converter, but you may also experience fouled spark plugs or engine pinging. Tapping the converter as mentioned previously can yield a rattling sound. The Check Engine light should come on when the catalytic converter has failed.