My 2005 with 160k miles has engine noise when cold. I talked to a couple specialists who said it could be valve noise another said valve noise would not abate when the engine warmed up. He suspected piston slap. A valve adjustment is pricey and the local independents are afraid to touch it given the complexity and needed shim packs. If it is piston slap I would be disappointed after spending a pile of dough to still have the same noise. Perhaps a stethoscope is in order or have I missed a possible cause?
Hi Timp1600. What grade oil do you use and what's the temperature like in Fort Collins? If it's not freezing then you could try a *slightly* heavier oil and see if that helps. There are high mileage oils available that are generally just a little bit thicker. You should also check that your oil is filled to near the top dimple on the stick (but don't over fill!). Several people have reported slightly noisier engine when the oil is only about half way on the stick. Engines generally make more noise when they're cold, and also they get a bit noisier as they age.
Nothing about piston flap or valve adjustments. During warm-up the valve and ignition timing varies a lot to allow quick warm up of the catalytic converter. By these timing changes, the engine combustion cycle is modified and thus the engine sound. If you stand at the rear of your Prius during this warm up, the tailpipe note changes a bit. Read 'Background' on this page : NHW11 Prius Temperature Hack Don't be fooled by those conventional car mechanics, the Prius as a bit more technology than a lawnmower !!!
Piston slap? The mechanic must work on alot of GM trucks. lol I owned and raced them. They truly did have a piston slap problem. Like suggested above, maybe try a thicker oil and see if that helps. Mine is a little noisy upon cold startup as well but the oil condition always looks good. Power and mpg are normal so I'm not going to worry about it.
It is likely that the valves need to be adjusted, as the clearance typically loosens up with engine wear. If this bothers you, you might ask your local Toyota dealer's service dept for a quote. However the valve adjustment will probably cost ~$500 or more since both camshafts need to be removed if adjustment in fact is needed. I would not go to a thicker viscosity in the Colorado winter, as this risks an engine no-start situation (DTC P3191). If you find that the noise goes away after the engine warms up, and your engine performance and mpg are acceptable, then I personally would not worry about this.
Clean the oil control valve filter before doing anything major. A clogged OCV has been known to cause a lot of clatter in other 1AZ engines, without setting a code. http://priuschat.com/forums/gen-ii-...eshooting/81138-vvt-oil-filter-poor-mpgs.html There are a couple of good independents in the Denver/Boulder area: Slipstream Automotive, and Adopt-A-Part.
