Academic / esoteric question on early Toyota timing belt engines

Maintenance/Repairs
1

As I search for my next old Sienna, the question about the consequences of a timing belt failure loom large. Specifically, which ones have interference engines.

For the record, my 1999 Sienna with 331,201 miles on the clock has a belt installed 8 months ago. So no need to advise me to replace the belt in that engine… just in case. It has 3500 miles on it. Replace the car…yeah, maybe, but at least for now I don’t have to worry about the belt breaking.

My purpose here is to find authoritative information from experts, clarifying unverified bits I’ve found about early Sienna timing belt engines, in relation to the VVTi design.

Here’s what consensus seems to say:

From what I have found from uncertain sources, the 1998 - 2000 (first generation) Sienna 3.0L engine is a non-interference design. If the belt breaks, you’re stuck. Get a tow, have the belt replaced, and you’re back in traffic.

For the 2004 - 2006 Sienna (second generation) 3.3L engine with VVTi, I’ve found fairly convincing information that this IS an interference engine and that if a belt breaks, the damage is extensive and thus probably not cost effective for a car that old.

That leaves the 2001-2003 (first generation) 3.0L engine with VVTi.
I have no information on the interference risk for that engine.

I don’t know much about VVTi, except that it must have some performance / efficiency advantage.

What I don’t know is if VVTi itself is a design which makes a Sienna engine susceptible to valve damage if a belt breaks. That is:

• is VVTi the design that creates the Interference problem?

• or is the 3.0L engine a non-interference whether VVTi or not?

2

According to the Gates website, the 2001-2003 Toyota 3.0 L engine is not an interference engine.

Tester

3

VVTi is a mechanism that varies the timing position of the camshafts. The result is a more powerful and fuel efficient engine. This tends to move the valves closer to the pistons in operation. If the belt breaks when the valves are close, they get bent or punch throught the piston when the piston smacks them.

The bottom line is unless the seller has a reciept for a recent timing belt change, assume it isn’t done so plan for one.

1 Like
4

Thanks @mustangman. I knew some but not all of what you wrote, and appreciate your explanation. I had a general understanding that VVTi changed the timing of valve movement.

The question is – specifically in the 2001-2003 Sienna engines – do the valves actually get in range of the pistons? @Tester says above that Gates described those engines as non-interference.

Before I posted this question, I called one well established Toyota dealership asking for first the service department and then the parts department person, with no luck: none would talk with me. It just occurred to me that someone in the local automotive machine shop might have an answer based on work experience.

As for your timing belt advice, that is exactly my position. Prove the job was done, or I have to judge the price for the car as including the cost of a t-belt job.

Your reply was helpful, thanks!

1 Like
5

Thanks @Tester.
Hmmmmm. How confident would you be in Gates’ catalog on this? Valve / piston clearance in a specific engine is not really their business.

I admit that a big part of my curiosity about this question is when contacting sellers, I already know more than they do. I know you can’t just inspect the belt visually to judge its condition. I try to explain the consequences of a broken belt: late at night, or in rush hour traffic, or far from civilization, etc. I’ve given up on that mission! And it seems that there’s widely varying time and mileage specs for replacement intervals.

6

The non-VVT 3.0L engine used in the Camry and Sienna is definitely non-interference. I don’t know if the VVT version is interference, and it very well could be. If I was in the market for a used Toyota Sienna, I’d go for the 1998-2000 models which don’t have VVT.

7

Thanks @bcohen2010. This much I already knew. I wanted to see if someone here could conclusively answer the 2001-2003 interference question, primarily so I knew, not that I necessarily would buy – or avoid – one of those. Still might, but I’m remaining flexible.

The reason I ask this question about interference engines is so that if I’m talking with a seller of a 2001-2003 car and discussing the T-belt, I’d like to be accurate if I say a broken belt will – or will NOT – create catastrophic damage to the engine if the belt breaks. Even if I don’t buy, I like to explain why replacing the belt is so important.

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Hi Tester:
Can you provide the link that you used?

For years, Gates had their timing belt guide right on their website.
Now I can only find copies of it on non-Gates sites.
I’m wondering if Gates no longer publishes it, or if I’m doing something wrong.

Thanks.

9

COULD be damage. There’s a chance there won’t be. I’ve seen a belt break on an interference engine and the valves stopped in a good position so there was zero damage. Replace belt and drove on.

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Click in the VEHICLE PARTS SEARCH button in the upper right.

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Thanks jtsanders:
That does allow you to find the Gates belt (and other parts) for your vehicle, though does it state whether a specific engine is interference or not? I don’t see it.

For example, a pdf guide like this was always available on the gates.com site, which highlighted the interference engines. It looks like the last copy was in 2010.

https://images.oreillyauto.com/parts/img/documents/gat/gatestimingreplacement2010.pdf

1 Like
12

Looks like the only Toyota interference engine from 1994 through 2010 is the 4.7 L V8, according to Gates.

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Just curious, where did you find that info?

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https://pdf.directindustry.com/pdf/gates/timing-belt-replacement-interval-guide/4801-975291.html

Tester

15

Thanks Tester.
I did find that copy. That site is a generic catalog site which happens to have a 2010 copy of what Gates used to publish on their gates.com site.

I’m puzzled why Gates removed it from their site. I wonder if they wanted to get out of the business and risk of stating which engines were interference or not.

16

Have you considered getting one with the 3.5L which has a timing chain so you don’t have to worry about replacing timing belts?

From what I’ve read, it’s the VVTi that allows for a scenario with the1MZ-FE where the valves could contact the piston if the belt were to fail at a certain time. 1MZ-FE’s without VVTi do not have that problem.

3 Likes
17

Could someone explain why the VVTi would be any more likely to have interference? My understanding is that the valve timing is altered, not the total lift, so I don’t see why VVTi would turn a non-interference engine into an interference engine.

18

I’m doing a little digging and the part number for the timing belt is the same for both variants, but the cylinder heads are different for non-VVTi vs. VVTi. Valve guides, seats, and lifters are all the same though.

Further reading on various toyota forums, is inconclusive. Some people swearing up and down that all 1MZ-FE’s are non-interference with others saying that the VVTi variants are interference and the non VVTi’s are non-interference.

I’m not hugely knowledgeable on Toyota engines. But I do know that the later 3.5L 1GR/2GR that was available on the Sienna has a timing chain, it’s the one I would go with.

19

OK, thanks for the refined explanation.

20

I’ve been trying to remember that. If it was not right here, then most likely (but I’m not certain) on the youtube channel “TheCarCareNut.” The channel is run by a man who was a long-time Toyota master diagnostic technician at a dealership. He then opened his own shop outside of Chicago (TCCN Automotive) which now is highly successful. Then came his YT channel, now with 1.38 million subscribers. AMD (the shop owner and presenter on the channel) gets relentless praise from his viewers and his customers.

Anyway, bottom line…I’m not sure where I heard that.

I just called a local Toyota dealer and spoke to a service advisor who said he’s been working for Toyota a very long time. The first thing he said was that in all his time, he’s seen very few belts break, and when they DO break, it’s at start up, meaning low RPM, and probably no damage. If that’s accurate, at least it puts to rest some concerns about having a belt break when you’re driving in heavy traffic. But he did not distinguish between the three engines in question: early 3.0L, 3.0L w/VVTi, and 3.3L w/ VVTi.

So he didn’t fully answer my question, but his experience eases my concern about a belt breaking.

And that is supported by one Sienna that I posted about here a year ago: a 2004 with under 80,000 miles, still running the original belt. Plus my own 1999 Sienna which I estimate had the same belt for about 13 years before I had it replaced at 323k.

I would think that there might be some “official” Toyota documentation answering my original question, but I don’t know how to look for that.