Dear Tom and Ray:
I drive a 1995 Ford Probe with roughly 138,000 miles on it. According to my mechanic, the rattlelike noise I hear as I drive is the result of valve tap. My mechanic indicated that it would be too expensive to repair. Can you please explain to me what valve tap is, and what causes it? -- Michelle
TOM: Sure, Michelle. But before you put your car's affairs in order, so to speak, make sure it's not just "pinging" that you're hearing. That's a much more benign condition.
RAY: If you're only getting the noise on acceleration, try putting premium gas in the car, and see if the noise goes away or improves a lot. If it does, you might ask your mechanic to check the stuff that can cause pinging -- like bad timing, a plugged EGR valve or carbon buildup on the pistons. All of those things are fairly easy to treat.
TOM: You should be so lucky, Michelle. If the noise is there whenever the car is running, and not just during acceleration, then it probably is valve tap, more commonly known as "valve lash."
RAY: "Valve lash" is just another term for "slop," or "your engine is wearing out."
TOM: When your engine runs, there's something called a camshaft, which turns (some cars have more than one). The camshaft is what ultimately opens the engine's valves.
RAY: When you have lash, it means that there's slop somewhere between the camshaft and the valve train. And that rat-a-tat-tat sound you're hearing is all those worn-out parts slapping together.
TOM: If I had to take a wild guess, with almost 140,000 miles on the car, I'd have to put my money on either a worn-out camshaft or worn-out hydraulic lifters. Those things wear out because the car is old, you don't change your oil frequently enough or you let your no-good brother-in-law drive the car like an animal.
RAY: Camshafts and lifters are big money, Michelle. Your mechanic is probably worried that if you spend a ton of money on that stuff, the transmission might fall out the next day. And he could be right. He certainly knows the car's condition better than we do.
TOM: So, if you want to just keep the car running as long as you can, we'd suggest two things. One is drive gently and keep the car away from your brother-in-law, that animal. The more gently you drive it, the longer it's going to take for those parts to completely wear out. It could last another 10,000 or 20,000 miles like this.
RAY: And the second suggestion is to explore the wonderful world of "last ditch" engine additives. For generations, people have used stuff like STP, Motor Medic, Lucas Oil Treatment and Newman's Own Salad Dressing to prolong the agony of a worn-out engine. So take a little shopping excursion to your local auto-parts store, Michelle, and try a few of them. You might find something that decreases the noise a bit. Good luck.