Toyota 3.5L V6 piston slap?

I thought issues like that were a thing of the past, from before computer controlled machining.

The piston slap noise is not the result of relaxed piston-bore production tolerances. The noise is the result of shorter piston skirts.

wrote in message news: snipped-for-privacy@v26g2000prm.googlegroups.com...

Piston slap is common on lots of engines these days. In an attempt to maximize fuel economy, engineers have worked to reduce piston to bore friction. This has been done by reducing the piston's skirt length (think height of the piston) and optimizing the piston to bore clearance for a warmed up engine. The 3.5L V6 has aluminum pistons and iron liners. They expand at different rates, plus the pistons are no cooled directly, so they run hotter than the bores. Since aluminum expands at a higher rate than iron (steel), the piston to bore clearance is greater when the engine is cold. This increased clearance along with the shorter skirt allows the piston to rock slightly in the bores. As a piston passes top dead center and bottom dead center the trust angel of the rods change direction. This causes the piston to shift angles in the bore. The pistons shift so that the bottom of the skirt swings from one side of the bore to the other (opposite side of the piston now rides against the bore). If the piston is slightly loose in the bore, the piston can build up enough speed during this shift that it strikes the opposite side of the bore with enough force to generate an audible noise. Many older engines (including Toyota engines) had so much lifter and chain clatter that you could not hear this noise, even if it was present. And many older engines ran tighter clearances, which reduced the noise when the engine was cold, but increased friction and hurt fuel economy. And many older engines had longer piston skirts that limited the piston's angle changed, but the longer pistons were heavier and had higher friction, again decreasing fuel economy.

I think every manufacturer is hearing complaints about piston slap. Even with really good machining techniques, there is some variation in piston to bore clearance. When you are trying to run at the perfect clearance, a few are going to miss. In general if the piston slap noise goes away shortly after you start a cold engine, it is nothing to worry about. If the noise persist after the engine is warm, you probably need to have an expert check it out. It might not be piston slap at all.

Same basic engine. I would expect it to behave in the same manner. This is really nothing new. A couple of years back when I was shopping for a pick-up I test drove three V8 Tundras. All three exhibited marked piston slap noise when started. The salesman told me they all did that and not to worry. Interestingly Ford replaced thousands of engine for this same concern - I guess Ford owners just weren't used to the rap rap rap of quality. I did not buy a Tundra in the end. I ended up with a Nissan Frontier - which makes the piston slap noise on cold morning....errrrrrrrr. I've learned to live with it.

Ed

Excellent and informative reply - thank you.

"Scott in Florida" wrote in message news: snipped-for-privacy@4ax.com...

I run 5W30 synthetic in my Frontier. It made no difference in the rapping sound on cold morning compared to conventional 5W30. A few years back a lot of people in an Ford Expedition mailing list I follow complained about 5.4L Ford engines and piston slap. Ford claimed it would not hurt durability and based on what people say in that list have reported over the years, I think it has proved to be true. Some people in that list tried synthetic to combat the noise - some claimed it made a difference in the noise, some didn't. I tend to think it shouldn't. Two lines of thought - when really cold, synthetic is likely to be less viscous than conventional oils of the same rating (they should have the same viscosity at 0, but probably not at -10). This could mean the synthetic oil won't provide as much of a cushion, thereby increasing the noise. Or, that because the synthetic oil flows better at really cold temperatures, it will coat the bores sooner and help dampen the noise. My personal experience was that there was no consistent detectable difference between a synthetic oil and a good quality conventional oil. My last Expedition would do the rap very briefly on cold NC mornings (but cold in NC is not really all that cold). I played around with different viscosities, and sort of, kind of, thought that maybe 5W30 Mobil 1 reduced the occurrence of the noise compared to 0W20 Motorcraft synthetic blend, but honestly I don't think it is provable.

Ed

It might actually make things worse....I wonder if the bores wouldn't warm up more than the pistons, increasing the clearance, or maybe because of the differential expansion rates reduce it. Might depend on how cold it is outside and how powerful a block heater. Interestingly my first Expedition actually came with a block heater, which I never used. But then it never had a problem with piston slap in the 149,000 miles that I owned it.

Well if you have really good sound insulation (like in a Lexus) you probably shouldn't hear it anyhow. And if you have an egg better with no sound insulation (like a 1992 F150 stripper with the 300 inline six), then the other mechanical noises probably cover it up.

Ed

In 1994, I bought a new Jeep Grand Cherokee with a straight 6 and the piston slap was consistently noisy and sounded like a diesel even after warmup. To me, excessive noise usually means wear of some sort. If you shouted loud enough, Jeep would extend the engine warranty to 100,000 miles.

Dave C.

Excellent detail. This still points to excessive piston-bore clearance. Maybe Ford fixed it by using the more expensive hypereutectic pistons, which seems to be the case looking at Mahle pistons clearance specs instead of the cheaper Aisin pistons specifications.

Still waiting on a recall on the new 6 speed transmission on the ES that flares. The 3.5L engine piston slap on cold starts. Keep being told the piston slap is normal

I will give them credit, they recalled the front driver side floor mat because it jammed up the gas pedal. But, that was only after the Federal Government did a full investigation and they were forced to do so. __________________

2007 Honda Pilot EX-L (wife's)