Piston Slap: "Clacking" About Piston Slap

TTAC Contributor David Holzman writes:

Sajeev, my ’99 Accord (2.4L 4cyl, 170k) when cold makes noises that sound like slightly loud tappets. If the engine is around 10 degrees (scan gauge) when I start the car, I’ll hear it. If the temp is more like 30 degrees or above, if I baby the car until it’s around 140-150, I won’t hear anything, but if I push it, I’ll get the noise fairly loudly. So I don’t push it. When I described it to Ray Magliozzi (Clack, from NPR’s Car Talk show) he thought it was piston slap. What do you think?

The noise is gone when the car is close to warmed up. The one thing that worries me a bit is that there was a point where I was driving much more than usual (though very easy driving, country roads around 40-50mph mostly, 23 mile trips) and I didn’t go to change the oil until I’d put 8000 miles on it, and the oil was around two quarts low.

I don’t remember having the noise right after the two quarts low, but when I first remember noticing it, it wasn’t very loud at all. It is loud now if I push the car at all when the engine is very cold (like 10-40 degrees), but as I said, I don’t hear it at all after the car is near warmed up. Uses maybe a quart in 3000 or so.

If it is piston slap, here’s one question. I consider it my duty to teach kids to drive sticks, and since I’m spending several weeks at my sister’s in February, I was planning to start teaching her younger boy to shift. (He doesn’t even drive yet.) Is this going to hurt my engine? Or anything else?

Sajeev answers:

Let’s get the easy question out of the way: a warm (operating temperature) engine is difficult to damage by a novice stick shift driver. I wouldn’t even bat an eye at that. The condition of your clutch, pressure plate and even flywheel is a whole ‘nother story. If all that stuff is quite old, the novice can send it to an early grave.

You might have Piston Slap, there’s some Internet chatter about Honda’s F22B1 motors to that effect. But I have my doubts, a bad lifter or a valve adjustment issue (address this at the next timing belt service) is my concern. And I say this not to contradict Ray Magliozzi.

Okay fine, maybe I am doing that just a little. But you mentioned the motor ran for a while missing 2 quarts of oil. Overhead cam motors (more so than other designs) are sensitive to low oil pressures when lubricating the top end (valve lifters, etc). It also explains the problem: cold engine oil, low levels, and the tough winter we recently experienced.

It is piston slap or just a worn engine? Tough call: either way, you gotta live with it. I’d throw a bottle of Lucas Oil treatment in there just for fun. I had good experience with Lucas silencing a noisy main bearing in one of my cars. If it doesn’t shut up that noise, you’re only out a few dollars. Good luck!

(Send your queries to mehta@ttac.com)