I have a 2000 Avalon XLS with 150,000 miles on it. When the engine is cold (I live in central FL) it has a "clacking" sound at 2300 to 3000 rpm. It doesn't happen when engine warms up to normal operating temp, or at any other RPM's. I've been using synthetic oil for the past 50k miles. Could this be caused by "SLUDGE". Thanks guys.
Piston slap? Try a slightly heavier oil. Maxlife synthetic comes to mind.
I'm not sure, but I have a MAzda thatr does the same thing. In the Mazda's case, the valves are actualed by a set of Hydraulic Lash Adjusters, a vlave type thing that fills with oil. After lots of cold-starts or trips under 5 miles, the HLAs lose the oil in them and partially collapse. Since there is now a space between the adjuster and the valve shims, the thing clacks like an SOB!!
Changing oil more frequently helps, Marvel Mystery Oil helps, but the thing that helped the most was driving the car for longer trips.
I don't know if the Avalon uses a system like this; I would investigate more. I found out by Googling "Mazda 2.2 clacking" and got a LOT of hits!
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