I have a 2005 Prius with 154,000 miles. The oil has been changed regularly and most of the miles are highway miles. My engine makes a slight knocking noise when it is cold that sounds a lot like my old Toyota Camry and a Subaru I drove recently, both diagnosed with piston slap. I have done some internet searches and have not run across anything about piston slap in these engines. Could it be something else? It is definitely engine, not accessories because it increases with RPM. Any others have similar issues?
Probably not, its not really seen in these engines unless i guess if the person who drives it doesn't care for the car; then anything could go wrong. What kind of knocking would you say that you notice
It sounds like it comes from the upper end of the engine. Not a bottom end knock. It disappears when the engine warms up. It sounds like piston slap I have heard in other engines or like noisy hydraulic lifters. I am assuming this engine does not have lifters since it has overhead cams.
The engine valves probably have excessive clearance. The valve clearance can be adjusted which requires removal of the two camshafts and replacing the "buckets" which provide the appropriate clearance.
Remove the camshafts? That's nuts. What were the engineers thinking? I wonder why they didn't make adjustable rockers? Do the "buckets" come in different clearances? I guess it would make sense that the clearances would decrease after the engine warmed up. Thanks for the information
In my 2005 Prius with 85,000 miles, the valve clearance "tick, tick" sound increases as the car gets warmer. I too have heard piston slap in my older / high mileage engines. My Prius does not have that at it's current mileage, but I'll bet that is the sound you are hearing. The good news is that it's not really a problem unless the engine starts to use a lot of oil. As you know, it very important not to let the oil get low. Modern cars, like the Prius have pistons that are oval when they are cold. This is because the piston contains more metal where the connecting rod pin goes through it than the rest of the piston. This results in a different expansion when the engine is fully warmed up. So, the designers make the pistons so they are round when they are warm. I have heard brand new cars with cold piston slap, but that is not normal for the Prius. This means it takes only a little wear to get piston slap in a cold engine. If you have piston slap in a warm engine, there is quite a bit more wear, but the engine is still not terminal until the oil consumption goes up. When my car starts to have cold piston slap, I will change it over to a "high mileage" oil with additional anti-wear additives and anti-carbon additives. In conclusion, don't worry, just watch the fluids. Enjoy your Prius, Dan
