Prius Lifter Tick vs Piston Slap

I have a 2008 Prius that has been gradually getting louder with either a lifter tick or a piston slap. What is the best way to tell the difference between these 2? The noise is the worst when first starting in the morning and when accelerating at lower speeds. My husband recently changed the oil and tried on 5W-30 Magnatec as well as SeaFoam with no change. What is my timeline for both of these conditions as far as needing to get them repaired? Of course, our other car is having issues right at the exact same time so we are trying to gauge what is the most urgent issue between the two.

Take the plastic engine cover off and start the engine cold.
Listen close to the engine and you can hear lifter ticking coming right through the valve cover.
Don’t confuse it with the fuel injectors clicking.
There should be a very soft clatter coming from all the valves.
Piston slap will have a deeper tick sound and won’t be so focused as to where it’s coming from.

The noise is the worst when first starting in the morning and when accelerating at lower speeds.

Sounds like piston slap. My nephew’s '97 Civic started this years ago. It sounded pretty awful going up a driveway first thing in the morning, but quieted down to almost nothing after 5 minutes. He ignored it and it’s actually been much quieter the last few years. Go figure.

How many miles on this car?


A lifter tick usually has a tinnier sound and is more rhythmic than a piston slap. While not true in all cases, if the engine is revved a bit and let off quickly a piston slap often comes across as a bit of an erratic rattle. It may sound like a rock being shaken in a can.

A small exhaust leak can also mimic a lifter tick to a tee.

Maybe the valve lash needs to be adjusted.

I drove a Chevy pickup for several years with what I thought was a “piston slap” noise. When I tore down the engine for an overhaul…I discovered that the “slap” was actually a loose wrist pin. Sometimes you just don’t really know until you actually know.