Teflon tape on hydraulic lines? Forget about it!

Dear Mike: I’ve got one rubber brake line that keeps leaking. It’s fine for a few weeks, but eventually the fitting to the hard steel line starts to leak.

I’ve replaced both lines, one at a time. Should I use a thread-locking compound or maybe some Teflon tape?

— T.W., Plano, Texas

A: Never, never, ever use Teflon tape, thread locker or any kind of pipe-joint sealer on hydraulic-line fittings. These fittings seal not on their threads, but on the tapered boss on the end of each carefully machined fitting. Make sure that the threads are clean and free of oil or grease by spraying them with brake cleaner.

Why are your lines coming loose? I’ll guess that you’re installing them incorrectly.

The fitting on the end of the steel line will spin freely on the line. The fitting on the end of the rubber line is crimped and won’t spin even a little. If you hold the steel end motionless and spin the rubber line to tighten it the last quarter-turn or so, the rubber line will be twisted along its length. Every time you depress the brake pedal, the line will swell slightly with the enormous internal pressure generated by applying your brakes, easily on the order of 1,000 psi. This internal pressure will force the twisted line to try to straighten itself out, and eventually it can loosen the fitting.

Look at the hose and you’ll see that it has print roll-stamped along its length. Be sure that this line of print isn’t spiraled like a corkscrew. Start by tightening the lower end of the hose. Don’t install the clip or tighten the jam nut where the hose goes through its bracket at the other end. Let the hose spin freely along its length.

Hand-tighten the fitting on the other end, then wrench-tighten it by holding the nonrotating fitting fast with one wrench and spinning the rotating fitting with a second wrench. Now you can add the clip or fasten the jam nut to anchor the fitting to the bracket.

Dear Mike: What would cause excessive sludge in my car’s engine? Is there anything else, besides lack of oil changes, that would cause it?

— V.H., via e-mail

A: Off the top of my head, four possibilities come to mind.

•1) Too many short trips. At least once every couple of weeks, you should drive your car someplace far enough away to get the engine hot and keep it hot for at least 45 minutes. This will raise the oil temperature high enough to boil out all the water and unburned fuel that collects in the crankcase at lower temperatures. Needless to say, this is especially important during the winter months.

•2) A broken or missing thermostat that makes your engine take too long to warm up, if it warms up at all during cold weather.

•3) A bad PCV valve that doesn’t purge the crankcase of water vapor and partially burned fuel. Some vehicles are known to have issues with PCV systems that freeze during cold weather.

•4) An engine that runs excessively hot. This can overcook your oil and make it thick and viscous.

A few engine designs are notorious for excess sludge, even when everything is working properly. And oil changes are, as you suggest, essential: The everyday use of a car for shopping or commuting qualifies as severe service, so oil changes should follow the manufacturer’s recommended severe-service schedule.

Dear Mike: I’ve heard that, once you replace your windshield, breaking the factory seal, there’s no guarantee that the car will be safe in an accident. True?

— D.P., via e-mail

A: Not true, with certain caveats.

Most modern cars and trucks rely on the stiffness of the windshield safety glass as an important element in their rollover protection. There’s some pretty advanced technology in the adhesives used to attach the glass to the cowl and the windshield surround, and it’s not a job for some bozo with a caulking gun full of bathtub sealer. It’s also important to not drive the car for a few hours after installation.

That said, a trained technician armed with the correct cleaners, adhesion promoters and adhesives can replicate the factory seal. Windshield replacement is a job for a pro, though, so deal with a shop that does the job properly.