Toyota Tundra Forums banner
1 - 20 of 42 Posts

· Registered
Joined
·
95 Posts
Discussion Starter · #1 ·
Hey guys, ive finally scheduled my timing belt replacement next week at the dealer, im at 145k miles and planning on doing alot more towing pulling our 4500lb camper this year and decided to go ahead and get it done. But my question is have any of you actully seen or heard of a timing belt breaking ? Seems like everyone freaks out over changing it exactly when its due and i do agree that its cheap insurance compared to a new engine but i had a 97 tacoma that i didnt get changed until it had 200k miles on it, only because i never knew about it needing changed until around that time. The belt was still in great condition and i hit the rev limiter more times than i could count being a teen/20 something put a lot of stress on the truck and it still looked great? so just curious as if to anyone has ever had a problem with one breaking on a sequoia specifically
 

· Registered
Joined
·
74 Posts
I've heard of them breaking. I think its recommended to be changed at 100k miles, and you're supposed to change the water pump at that time as well because they've done all the labor to get to it already, so it'd save you some money. But yea, I've also heard of the belts lasting for way past the recommended change interval. Its just a risk not changing it after a while.
 

· Registered
Joined
·
12 Posts
I had one break on my '92 Prelude while doing about 85mph. Car had roughly 190k and probably had never been changed. Being an interference engine it was bad news, ended up selling the to my mechanic for a few hundred bucks. Would have cost $2500-3000 to fix all of the piston/valve/head damage.

When I bought my 01 Sequoia with 167k, the timing belt was the first thing I had done for peace of mind. If I remember, it cost $600-700 to have that done with the water pump and serpentine belt.
 

· Registered
Joined
·
47 Posts
Definitely change it. Interference engines are nothing to mess with. If it breaks, it's bad, like new engine bad. More than likely, if the timing belt has had no foreign fluids get to it, it would be good for over 200k - possibly. Problem is you can't see it, so you never know. Too many variables to tell. That's why they have the recommended intervals. Just make sure they tighten down the crank pulley bolt to spec as that can open a whole other can or worms. I don't recall too many timing belt failures, probably more headgasket failures etc. than that.

Or you can do it yourself, save some change, get intimate with your truck, and impress the hell outta your wife. Finish it up, start it up, pop a top on an ice cold one and be like "I'm the f#$kin man!"
 

· Premium Member
Joined
·
2,846 Posts
Toyota recommends a particular interval for a timing belt replacement to avoid liability for failure and to avoid the adverse reputation that failures would generate. Here's how that scenario works:

Stage 1: Timing belts break and engines are destroyed. This happens on belts with less use than the recommended interval.

Stage 2: A meme develops. The synopsis is, "Don't buy a [fill in the blank]. The timing belt breaks and the engine blows up." No further thought is involved; memes are like that.

Stage 3: The meme expands. The synopsis is, "Your honor, my timing belt broke before it was supposed to be replaced according to Toyota. Their incompetence in recommending that interval cost me [fill in the blank], and I ain't the only one been hit by it."​

Now, how would an engineer investigate the longevity of the timing belt to recommend the recommended replacement interval to avoid this? The idea is to make the interval short enough to prevent failures, but long enough to not deter sales. It's easy in principle, but difficult and expensive in practice. The steps are:

Step 1: Drive a group of test vehicles until the timing belts break. Note the mileage on the each vehicle when its belt breaks.

Step 2: Examine the distribution of mileages when failure occured. Very likely this would be a Gaussian distribution, which is characterized completely by its mean (i.e. its average) and its variance (i.e. its dispersion about the mean). The standard deviation is the square root of the variance.

Step 3: This is not intended to be a discourse on statistics, but the core of the method is quite simple. If the distribution really is Gaussian, then the probability of a timing belt not breaking if it is replaced at six standard deviations less than the mean time to failure is 99.99966%. The probability of failure is one in 294,000. So, the recommended replacement interval is set at least six standard deviations lower than the mean miles to failure.​

Now, is this what Toyota did? Likely not. To use this method, one has to have enough data points to characterize the distribution of failures. That means testing lots of engines to destruction in real-world use. That expensive. What's worse, it takes a very long time. As we've all seen here, vehicles have survived with original timing belts long after the recommended interval. Think about that carefully. The first generation Tundra could be out of production before sufficient sampling was complete, and yet we find a recommended timing belt replacement interval in the owner's manual of the first one off the assembly line back in 1999.

So, how did Toyota determine a recommended replacement interval? I don't claim to know. I suspect it was a combination of: 1) observing wear vs. mileage on the belts of engines that did not fail; 2) comparing that to their own long history of producing engines with timing belts; and, 3) extrapolating a mean time to failure and an associated variance. That is much less expensive, and it can be done very rapidly, as the mileage required is much less.

Now, what should you do, and why should you do it?

If you replace your timing belt at the recommended interval, you should expect to find that it is not near breakage, because it should not be near breakage. If it was near breakage in the typical case at the recommended replacement interval, it would mean that Toyota vastly overestimated the proper interval. The fact that we don't see rampant breakages means Toyota didn't overestimate the interval.

The problem you face is that you don't know if your own case is typical. The analogy to help understand this is that statistics can tell you, with great accuracy, how many people in your city will die of cancer next year, but it cannot tell you if you will be one of them.

All you can do is gamble, and I don't gamble, so I use a simple risk/benefit analysis.

I expect to keep my '00 Tundra for about 250,000 miles, at which time it will be 24 years old. This requires two timing belt replacements using the recommended interval. I have changed it twice. If I were to stretch the interval, I would derive zero benefit unless I stretched it such that I changed it only once, thus saving the cost and labor of one change. Minimally, that would be an interval of 125,000 miles, and I would face selling it while it has a belt with 125,000 miles on it. If I still changed it twice, but at a longer interval than Toyota recommends, it would mean that whoever I sell it to would get more use out of that final belt and I would get less, which benefits him more and me less.

Bottom line: Lengthening the interval means risk without benefit. I'm an engineeer, and to me, that is a poor tradeoff.
 

· Registered
Joined
·
767 Posts
I completely agree with DJ on this.

One thing to consider is that a timing belt may never have a catastrophic failure and completely destroy an engine, but they will stretch over time. I think one of the difficulties in justifying the replacement of the belt at 90 or 100 k miles is that everything seems fine, and it is one of those unseen things on your truck.

I for one would much rather spend the $800 or so on wheels than a timing belt replacement, since I can look at them every time I get in the truck, but in the long run, the belt would probably be a better investment.
 

· Registered
Joined
·
83 Posts
To answer your question - no, I have never personally witnessed a automobile timing belt fail. I have seen timing belts fail plenty of times on industrial equipment.

The timing belt will look perfectly fine until the day it breaks. When I did the belt on my Sequoia I found the water pump had been leaking; I've seen several posts from others indicating the same. So, you can wait for the belt to fail and bend valves; or wait for the pump to fail, overheat, and have failed head gaskets; or replace the belt and pump within a reasonable mileage as recommended by the manufacturer.
 

· Registered
Joined
·
74 Posts
I'm at 140k with the original timing belt. My problem with getting it replaced is all I can expect is a 12k warranty, if even that long. And if the new belt breaks at 20k I am SOL. I'd rather take my chances with the original belt to at least 200k. Then I'll reconsider. Everyone ASSUMES the dealer techs are perfect and never make mistakes. I know better.
 

· Premium Member
Joined
·
2,846 Posts
I'm at 140k with the original timing belt. My problem with getting it replaced is all I can expect is a 12k warranty, if even that long. And if the new belt breaks at 20k I am SOL. I'd rather take my chances with the original belt to at least 200k. Then I'll reconsider. Everyone ASSUMES the dealer techs are perfect and never make mistakes. I know better.
Whis is more likely: 1) a belt with 140K already on it will last 60K more; or, 2) a new belt will be installed correctly and last the 90K that it's supposed to be changed at?

When you think about that comparison, consider how many times a failure due to EITHER of these two scenarios has been reported here.
 

· Registered
Joined
·
47 Posts
Whis is more likely: 1) a belt with 140K already on it will last 60K more; or, 2) a new belt will be installed correctly and last the 90K that it's supposed to be changed at?

When you think about that comparison, consider how many times a failure due to EITHER of these two scenarios has been reported here.
Yes and yes to #2. AND if it does break you have someone to hold accountable. But do a little research, read some how-to's and do it yourself! No one cares about your truck like you do and you learn something!

DJ, I love all your posts and from one engineer (civil) to another :tu:
 

· Registered
Joined
·
1,434 Posts
I'm at 140k with the original timing belt. My problem with getting it replaced is all I can expect is a 12k warranty, if even that long. And if the new belt breaks at 20k I am SOL. I'd rather take my chances with the original belt to at least 200k. Then I'll reconsider. Everyone ASSUMES the dealer techs are perfect and never make mistakes. I know better.
You're making a valid point. Right now you have a known good timing belt system. If you change it there's a non-zero probability you'll get either a defective new component or a botched installation.

As a mechanical engineer I'm sympathetic to this point of view. It has commonalities with the idea that you should never choose elective surgery as all surgery has a risk of complications or death.

Having changed a number of timing belts on different vehicles it's my opinion that the 2UZ-FE has a well-designed timing belt system with a relatively low risk of botched installation compared to, say, a VW diesel engine where special tools and a specific procedure are required. But still, I can think of several ways to botch the 2UZ-FE job (i.e. fail to pull the pin on the tensioner, fail to properly torque the crank bolt, etc.)

So, this got me thinking about the risk you're running by taking the original timing belt to 200K. I'll disagree with DJ and say I think it's unlikely that the timing belt system failure distribution will be Gaussian. Seems more likely to me that it'll be a Poisson (skewed) distribution. Nevertheless, assuming a normal (Gaussian) distribution will be close enough for some back-of-the-envelope estimates.

If you know (or assume) a couple of things about a normal distribution you can calculate anything else you might want to know.

So for entertainment purposes only here's my take on this.

Assumptions:
1) Toyota engineers knew what they were doing when they chose the timing belt change interval of 90K. I'll assume they chose a 4 sigma probability of failure at the recommended timing belt interval - i.e a probability of 1 in 33,000 that the timing belt system will fail before 90K miles.
2) There are reports of timing belts going well beyond 200K miles. I'm going to assume, based on these empirical reports, that the practical upper limit for timing belt life is 350K miles. So this is the assumed 4 sigma upper limit.

Then our assumed normal distribution looks like this. Mean of 220K miles and standard deviation of 32.5K miles.

With that information we can calculate the probability of failure of your original timing belt system before 200K miles. And the answer is - 27%.

And what percentage of 2UZ-FE timing belt jobs are botched? I'd guesstimate 1% to 2%.

So, do you feel lucky? Because the numbers say it's much riskier to go to 200K than it is to get your timing belt changed.

And then one more step. How far should you push your timing belt change interval? Let's say you're prepared to accept a 2% risk of failure. I might accept that risk. Then you should push your timing belt interval no further than 153K miles. At 140K miles you're already at a 0.7% risk of failure and the odds against you rise steeply from here.

I'd change it now.
 

· Premium Member
Joined
·
2,846 Posts
You're making a valid point.
That point is that one should put off doing routine maintenance because it might be done wrong.

That's a "trade-off", not a "point". If one advocates for it, then one should analyze it in terms of risk vs benefit.

Many years ago, a relative took a similar approach to delaying routine maintenance, not because of concern about doing it wrong, but because of concern about not being able to afford it. Regardless of the reason, the experience was the same either way. He and I had identical vehicles during that time. I did routine maintenance (I'm an engineer; we're often like that). He didn't. The cost of overhauling his engine (rings, pistons, bearings, cam, you-name-it) in about 100K miles was WAY more than the cost of the maintenance he avoided. My vehicle ran like a watch. It was a sobering lesson to both of us.

With that information we can calculate the probability of failure of your original timing belt system before 200K miles. And the answer is - 27%.
We don't have much in the way of real-world data on which to compute such probabilities. If this estimate is correct, then roughly 27% of those who try to stretch a timing belt (pardon the pun) to 200K miles should expect to experience failure and a ruined engine. We don't see that, at least not here. We keep asking for anyone to comment who has experienced a timing belt failure in a 2UZ engine, and so far, no one has (if I recall correctly).

I don't mean to belittle your attempt, but I think the probability of failure is even lower than you estimate. I don't think we have enough real data to characterize the distribution beyond that the mean is "fairly high".

I'd change it now.
That is my recommendation, but I don't make it on the basis of an estimate of probability of failure, other than to note that the probability increases with miles. I base it on the simple analysis that the tradeoff of risk vs benefit is overwhelmingly, in my unhumble opinion, on the side of benefit.

And, I don't belittle the risk of doing it wrong. I do my own repair and maintenance work, excepting only that which I don't have tools and such for (mounting and balancing tires, pressing bearings on and off axles, body work, painting, ...). My experience has been that dealership mechanics can be very good, but they can also be bloody awful. I've had a radiator broken, a battery broken, and a lug bolt broken. I've had axle seals replaced (I expected bearings would need replacement, but the didn't, so it turned into a seal-only replacement), only to have the new seals leak just like the old. Finally, one of my brothers has had his oil drain plug stripped four times during oil changes.

But, I note that dealership mechanics can be excellent, and usually do fine work. My other brother has been in the business 41 years, and tells stories of acts of idiocy that numb the mind. He also duly notes that the stories are told because they are the exceptions, not the rule, meaning that the overwhelming majority of repairs come out just fine.

To me, putting off maintenance because it might be done wrong is just whistling at the monsters in the closet to keep them away, because doing the maintenance resembles opening the closet and not seeing any monsters.

All that being said, let's look another aspect of it.

I put together a spreadsheet a few weeks ago in which I calculated the cost of ownership of my '00 Tundra. It now has 179,000 miles on it, and is in truly excellent condition. The NADA used car price estimator says it is worth about $8,500, so I presume I could sell it for the round number of $8,000. I included costs for purchase, insurance, fuel, additions, maintenance, and repairs, less the presumed sale value.

The net cost has been 41 cents per mile.

The net cost for two timing belt changes has been 0.87 cents per mile.

Thus, if I cannot afford the timing belt changes, then I cannot afford to own and drive the vehicle, either.
 

· Premium Member
Joined
·
2,846 Posts
Many years ago, a relative took a similar approach to delaying routine maintenance, not because of concern about doing it wrong, but because of concern about not being able to afford it. Regardless of the reason, the experience was the same either way. He and I had identical vehicles during that time. I did routine maintenance (I'm an engineer; we're often like that). He didn't. The cost of overhauling his engine (rings, pistons, bearings, cam, you-name-it) in about 100K miles was WAY more than the cost of the maintenance he avoided. My vehicle ran like a watch. It was a sobering lesson to both of us.
Oops. I had a phone call in the middle of writing this, lost my train of thought, and missed my omissions when proofreading, so I'm responding to my own comment.

My brother overhauled his engine five times during that 100K miles. He had a broken cam, then a burned piston, then siezed rings, then a warped head, and so on, one d**ned thing after another, all to reduce the cost of regular oil changes. Engines are better now, as are oil and filters, but the experience was an eye-opener, and we both do regular maintenance routinely.
 

· Registered
Joined
·
5 Posts
Funny that this is the 1st thread I saw today, I am getting mine changed at the dealer today. Belt, Water pump & thermostat, on my 01 with 186k miles & a fresh frame. Will post costs & details when I get it back. I estimate around $1000.
 

· Registered
Joined
·
1,434 Posts
I don't mean to belittle your attempt, but I think the probability of failure is even lower than you estimate. I don't think we have enough real data to characterize the distribution beyond that the mean is "fairly high".
With respect, I think the information available here is subject to selection bias as people who comment here have above average motivation to maintain their vehicles. We don't hear about the timing belt failures that aren't reported by their owners. Having said that you may be right that the average life expectancy of a 2UZ-FE timing belt system is more than 220K miles. If that's the case then your opinion offers encouragement to the procrastinators.

Engineers are a bit like lawyers in that the "correct" answer is usually the most conservative answer. If you want to get a handle on what the real risk of timing belt failure is you have to make some assumptions and as I said, my simple analysis was based on assumptions which are certainly open to question.

But I'm pretty comfortable with my original conclusion that Fritz_The_Cat should feel OK up to 150K miles but that at 200K miles he will really be starting to roll the dice.
 

· Premium Member
Joined
·
2,846 Posts
With respect, I think the information available here is subject to selection bias as people who comment here have above average motivation to maintain their vehicles. We don't hear about the timing belt failures that aren't reported by their owners.
The flip side of that is that such a post is conspicuous by its complete absence. It has been asked for several times and nobody has responded. That doesn't mean that it doesn't happen, but it doesn't give us a clue what the distribution of failure vs. miles is.

But I'm pretty comfortable with my original conclusion that Fritz_The_Cat should feel OK up to 150K miles but that at 200K miles he will really be starting to roll the dice.
This reminds me of a friend's experience with his '86 Camry (just like ours, but for the color). The recommended timing belt change interval is 40K miles (and it's easy, requiring perhaps an hour of work). He put it off, and it blew, in a relatively unsafe area. He called me from a pay phone and I yanked him to safety with a tow chain. It's a non-interference engine, so a few hours later he was back on the road. Risk vs. benefits ...
 
1 - 20 of 42 Posts
Top