The 3.5L wasn’t available until MY2007. CarFax shows MY2003 Siennas for as little as $3000 and MY2007 for as little as $5000. @WesternRoadtripper1 can decide if the extra $2000 is worth it to avoid a new timing belt, which might cost around $1000. If a new timing belt is needed or assumed needed on the 2003, that makes the difference much less.
It’s not the camshaft lift that will cause the issue, it’s the opening point of the intake valve and the closing point of the exhaust valve. Max lift for both intake and exhaust valves occur when the piston is well past (intake) or before (exhaust) TDC. The intake valve opens at +/- TDC and the exhaust valve closes at +/- TDC. If the VVT advances and opens the intake valve too soon or retards and closes the exhaust valve too late, relative to the non-interference engine, contact between the valves and pistons is possible. I don’t know the specs on the Toyota engines here but I’ve built a number of race engines where interference would occur with only a few degrees difference in cam timing.
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OK, I can understand how the valves might interfere with each other, but piston to valve is determined by lift, the timing doesn’t matter with a broken belt. The valve either hits or it doesn’t at max lift.
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If the camshaft lift specs, piston height-compression ratio, rocker arm ratio (if it has them), connecting rod length (same piston spec), cylinder block deck height etc etc are all the same as the non VVTi as w/VVTi, then they are either both interference or non interference engines…
If the valve at full lift does not come in contact with the piston when rotated 360/720 degrees then it doesn’t matter what the duration is or when the valve opens or closes…
Now, I did read where the VVTi had more duration @ 236/236 (intake/exhaust) than the non VVTi camshaft @228/228 (intake/exhaust), but can not find any lift specs for the non VVT vs the VVTi engines, but a lot of times (but not always) when you have more duration, you have more lift, so there’s that…
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Your logic makes good sense, except for this:
From what I heard on “The Care Care Nut” Youtube channel (mentioned in another comment), in the first two years of the timing chain engine there were numerous and varied problems.
“AMD” – the shop owner and former Toyota master diagnostic technician at a Toyota Lexus dealership, posted a video with his list for "Toyota’s BEST and Worst Engines." He states that the list is based on his own direct experience as a Toyota specialist. Watching some of his videos, you clearly see he has a heartfelt reverence for certain engines.
AMD’s list included the 2004-2006 Sienna engine. Not the 3.5L 2007-2008 engine.
Thus my preference.
See attached screenshot from the video.
He also says, at 2:20 in the video, that the VVTi is an interference engine.
Your logic makes good sense, except for this:
From what I heard on “The Care Care Nut” Youtube channel (mentioned in another comment), in the first two years of the timing chain engine there were numerous and varied problems.
“AMD” – the shop owner and former Toyota master diagnostic technician at a Toyota Lexus dealership, posted a video with his list for "Toyota’s BEST and Worst Engines." He states that the list is based on his own direct experience as a Toyota specialist. Watching some of his videos, you clearly see he has a heartfelt reverence for certain engines.
AMD’s list included the 2004-2006 Sienna engine. Not the 3.5L 2007-2008 engine.
Thus my preference.
See attached screenshot from the video.
He also says, at 2:20 in the video, that the VVTi is an interference engine.
Maybe it’s just that I have an old computer, but this website forum seems to be more and more clunky every time I log in. The proliferation of ads is part of it. But every time I post on a thread, I immediately see two versions of my post. One has my content in ordinary “black”, and on the other, the content is medium grey. Does that happen to everyone?
And after I’ve been logged in and take a break for something else and come back, like now, my typing gets far ahead of words appearing on the screen, the input is VERY slow.
The strangest one is that I had just posted a reply to jtsanders, then saw my reply directed to @davesmopar. Maybe it was my mistake, or not. Either way, my apologies to both.
Puzzling…
Later in the video, AMD lists Toyota’s worst engines. Here is the screen shot showing one group of engines to avoid: 1AR and 2AR.
Note Sienna 2010-2020 on this set.
If the engine has lasted for almost 20 years, would the issues still apply this late in life? Many problems apply to some, but not all mechanical assemblies. If a high percentage exhibit the problem then not all do. From what I’ve seen in the past from CR, a 4% overall failure rate divides the less than average from the much less than average ratings.
Not since I started using Duck Duck Go, But this is the only site I use it for, so far I have not had one ad and no slowing of typing…
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Also note that the 1AR is the 2.7L I4, that is very rare in the Sienna. It shouldn’t be confused with the much more reliable 3.5L GR, which is the engine you’ll encounter 95% of the time (in the years where both engines were available).
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You’re right. I was in full-on race mode (all engines were interference engines where I worked) when typing that and lost sight of the question.
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I’m fairly sure that all gasoline Toyota engines that use a timing belt are non interference. The interference engines use a timing chain.
edit: davesmopar’s response below is correct. There is an interference engine with a timing belt. Quote from the toyotanation.com froum: “The 3.3L 3MZ-FE engine is a rare example of a Toyota engine with timing belt that is an interference. In most cases, Toyota engines with belts are non-interference, but the 3MZ is a rare exception.”
You might want to do a little more research next time before posting…
2) Timing Belt Problems
We’re moving onto yet another issue that really isn’t a true design flaw. However, the timing belt is an important standard maintenance item. Toyota 3MZ-FE engines are interference engines. This means there is some overlap in the area in which the pistons and valves travel. This isn’t a problem when the 3.3 V6 ignition timing is on par.
Pretty sure that is a timing belt…
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Thanks @FoDaddy, good info.
I’m surprised to know that a 2.7L engine would be used in a Sienna.
Would that have helped Toyota lower its overall emissions from the entire Toyota line? Or was it a turbo engine that produced a lot more power than a naturally aspirated engine of that displacement?
Or just a big mistake?
What’s your source?
No, it was a normally-aspirated inline four cylinder, albeit a larger displacement I4. It’s inclusion probably had something to do with CAFE numbers, though it was only rated for about 1 MPG more than the 3.5L V6. Compare Side-by-Side It proved very unpopular and was only offered for two model years. In exchange for that 1 MPG increase, it gave up about 80 HP and about 60 lb/ft of torque. A fairly noticeable difference in a larger/heavier vehicle like the Sienna.
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Thanks for the reply @FoDaddy.
80hp less in a minivan weight over 2 tons seems ridiculous. I can see why it flopped.
Thanks for this @davesmopar. Glad to get this confirmation.
I’ll read the piece you attached.
For some driving environments 187 horsepower is sufficient. The 3.0 L engine in your Sienna is rated at 194 HP. The 2011 - 2012 Sienna has a 6-speed automatic transmission, yours has a 4-speed auto.
Consider how much easier it is to replace spark plugs on a four-cylinder engine.
It was a strategy to increase CAFE values, whether or not the goal was achieved is not known.