Timing belt question

For a 2004 Toyota Highlander V6.

Is it internal to the engine? Or is it the same serpentine belt on the outside of the engine?

I ask this for my 84 year old mom. She still drives, but very little. Just to the store and back. A bit more than that sometimes. The car is driven about once a week. It has 13,000 miles on it (no not 130,000). She was told by someone that it needs a new timing belt a year or two ago.

The car runs great. But considering age, instead of millage, is it time to have this replaced? If it’s just the ‘main’ serpentine belt, I’m all over it, but she was told that the timing belt needs to be replaced.

Yes you have a timing belt vs. a timing chain. It’s internal to the engine. Requires removal of the water pump/timing belt cover on most engines. Water pump is replaced at this time to save the labor of going in again later if that craps out.

Handy list for toyotas; belt vs. chain.


That said; Toyota recommends changing at 90k miles with nothing about age. A couple of toyota forum searches talk about 10 years for age for replacement even on low mileage vehicles. The belt is mostly synthetic with some rubber. They do age and breaking is expensive - engine may be toast.

The serpentine belt is the one you can see when you lift the hood. The timing belt is under a cover inside the engine block.
At 13,000 miles, I wouldn’t bother with it. They typically need to get replaced around 100k, but it’s probably coming up as scheduled maintenance because of the age of the vehicle.

The problem is Toyotas have (as far as I know), interference engines which means, in short, if the timing belt breaks, the pistons will smash into the valves and cause a lot of expensive problems. But, like I said, I wouldn’t bother at 13,000 miles, unless the mechanic has some other reason to be in that deep, like replacing the water pump.

The timing belt is driven by the engine crankshaft, and it turns the engine’s camshaft(s) (you may have more than one). The camshafts then push the engine’s valves open at the appropriate time, which lets fuel into the engine cylinders and lets exhaust out at the end of the engine’s cycle. It’s called a timing belt because it controls the timing of these various valves, when they open and close. They used to use a chain, but these days they use belts so that they can make the engine quieter and a bit lighter. The belt has “teeth” on it so that it keeps the spinning of the engine crankshaft (which is driven by the pistons) and the camshafts in perfect sync.

There are two types of engines, interfering engines and non-interfering engines. An interfering engine means that when the valve moves into its open position, it is in the same place inside the cylinder where part of the piston is. In a non-interfering engine, when the valves open, they open into a space where the piston never goes. I’ll take the previous poster’s word for it that you have an interfering engine. What this means is that if the timing belt breaks, then the valves may end up open when the piston comes up to the top of the cylinder. This usually results in the valve being obliterated, accompanied by severe damage to the piston and the inside of the cylinder. In a non-interfering engine, if the timing belt breaks, then the engine just stops running. Since the valves never move into the same area where the piston travels, all that happens is that the engine stops.

You have an interfering engine, which means that if the timing belt breaks, there’s a whole bunch of stuff inside the engine that can get very badly damaged. Basically, you can just about ruin your entire engine.

Changing the timing belt is a big job, because you basically have to disassemble the entire front of the engine to get to it.

When you look at the engine, you see the serpentine belt, which drives the alternator, power steering pump, and the compressor for your car’s air conditioning (that’s why the call it a serpentine belt, it snakes its way around all of those devices, plus maybe the water pump pulley and one or more tensioners). To change the timing belt, everything I just named has to come off of the engine, along with the pulleys and things that they are attached to. Then you have to take off the front cover of the engine. Now you can finally get to the timing belt. Usually, the mechanic will change the water pump while he’s in there, since you’ve already paid for the labor of disassembling the entire front of the engine and the cost of the pump is relatively cheap. You wouldn’t want to cheap out on the water pump and not replace it, and then have to spend all of that labor again later to replace it when it does fail. Once the timing chain and water pump are replaced, then the entire front of the engine has to be put back together.

Needless to say, this job costs a bit more than swapping out a new serpentine belt, so be prepared for a somewhat hefty repair bill. Again, though, not doing this repair can destroy the entire engine, and fixing that may be more than what the car is worth.

Since timing belts are made out of rubber, and even under little old lady minimal use that rubber will eventually rot and fail, it’s time to replace the timing belt.

ETA: Here’s a youtube video that explains changing out the timing belt on Toyotas similar to yours:

Thanks all.

It surprised me that my mom was told that the timing belt needed changed. Just from a cursory inspection. That’s why I wondered if it was tied into the main serpentine belt. Perhaps, she misunderstood, or the guy was laying on a layer of BS to a older person.

I don’t think it should need replacement. Yes, the car is 11 years old, but it only has 13,000 on it. And it gets driven weekly. She does not want to take it to a dealership, and is looking for local mechanics. She want’s me to take it to whom ever she finds. ehhh.

It’s an 11 year old rubber belt. It may only have 13,000 miles on it but rubber rots over time.

Get the thing changed.

Anyone know how you find out if your car has an interfering engine or non-interfering engine?

I have always wondered why a timing belt breaking is so bad for the engine, and engineer_comp_geek’s explanation is a good one.

However, I have to ask… Why would anyone not design their engines to be of the non-interfering variety? I assume it has a lot to do with money, but I would think cars that have a non-interfering engine would be more appealing to the consumer.

I had a roommate about 20 years ago that had his timing belt break on his subaru. He had to pay for the repair, but no permanent damage to the engine.

That was along time ago, and I am assuming his engine was of the non-interfering variety. I have no idea, because I don’t remember the model and I didn’t know much about timing belts at all. Apparently, I still have a lot to learn.

I’m facing this situation right now with a Car that has 108,000 miles in it but it’s so damn expensive. I had a 1997 Toyota Celica once that had the timing belt snap and it didn’t destroy the engine but I’m not sure if it was an interference or not. I think maybe it didn’t cause damage because it apparently broke on attempting to start the car rather than on the highway.

More compression, if I had to guess. The piston can travel further to the top of the cylinder. OR, it could also allow fuel to get in and exhaust to get out faster since the valve can open wider.

I’ve also seen some pistons that have notches cut out that make them not interfering since that’s where the valves come down. That could be a cost related reason, but it’s so minimal, I can’t imagine it’s the reason. After all the time spent milling a piston, I can’t imagine it costs that much more to drill out those notches.
Making the top less than flat might also change how much power is produced from the explosion. They’d also reduce compression.

ECG, I’m only assuming the OP’s mom’s car is interfering based on something I heard many years ago. I could be wrong.

I poked around on the internet and I’m finding posts saying it both is and isn’t an interference engine. It seems to depend on which engine you have. You’ll probably need to find out, at the very least, what size it is.

A google search will usually tell you. If not, you can always ask your local dealer. Their service department should be able to tell you.

Engines have to suck fuel and air into the cylinders and blow the exhaust out. There’s not a whole lot of room to play with at the top of the cylinder, so an engine that has larger valves so that it can more easily suck in air and fuel and push out exhaust will end up having those larger valves travel down into the same space where the piston comes up. If you use smaller valves so that you don’t have a potential interference problem, then it’s harder for the engine to suck in air and fuel and push out exhaust and your engine’s efficiency suffers.

If you leave more space at the top of the cylinder so that you can fit your bigger valves in, then that space stays filled with stale exhaust air as the engine goes into its next fuel intake cycle, again reducing the engine’s overall efficiency.

Designing a non-interfering and efficient engine is very difficult.

Agreed. And she’s putting a lot of short trips on it so that 13,000 miles represents a more than usual amount of heat and cool cycles.

A list of interference engines is here.

I found it and bookmarked it, thanks to engineer_comp_geek’s link to a YouTube video by a mechanic changing a timing belt who linked to the list in the video description.

I had a 2,000cc German Ford engine in a car that like clockwork would break its timing belt every 40,000 miles. I put 232,000 miles on it with no other engine work, except, probably a water pump (though I can’t recall). It wasn’t an interference engine, but those repairs didn’t come cheap, either.

They would break at the most inopportune times, naturally, such as on a prairie highway in January or in heavy traffic at rush hour in the middle of an intersection. In January. In a blizzard. While Mars attacks.

After that car breathed its last, I made sure I did not buy any car with a timing belt, especially those with interference engines. One hundred thousand miles before a timing belt fails is not written in stone. It could happen far, far earlier than that, and buying a used car with an interference engine means the expense of replacing the belt — or the engine — all the earlier.

Give me a timing chain and a non-interference engine or give me death (which could happen anyway, with a timing-belt engine).

They should be named suicide engines, not interference engines.

I did a google and it seems that engine had a interference design. That means if the timing belt does break or slip, the piston will slam into the valves. That will ruin the engine and cost a lot of money to fix.

On a non-interference design, the engine just stops running. Fixing the timing belt will get the engine up and running again. Of course having an engine stop running while driving in traffic isn’t a good thing.

It depends on the weather, but an old timing belt is probably starting to crack. A cursory inspection will probably see a number of beginning cracks. (Honda and Audi, IIRC, had a little port on top front of the belt cover that you could open and look into to see the state of the belt. The belt is fibre embedded in rubber, so a crack does not mean it will fail tomorrow, just that it could fail soon.

The vehicle should probably be inspected by someone who knows what they are doing every year or so, for just this reason.

I had a Honda Civic 1985, and the belt went with 105,000 km and 5 years 4 months on it. Guess what the warranty was? (Hint -100,000 or 5 years) I found out several years later the dealer should have told me to change it at 80,000 miles, but basically it was cheaper to buy a new car than do the head repair caused by the failed belt.

(The dealer’s mechanics were idiots. A friend said he was talking to one mechanic, the guy demonstrated how smooth the Honda engines were by turning the crank of one on the bench by hand… no timing belt on it … then it needed a valve repair job. )

OP here. Engine type is Toyota 3MZ-FE 3.3L. Timing belt is - external

Still trying to find out if it’s an interference engine, though I suppose it does not really mater since we are going to change it.

Kenm link (thanks) says there is conflicting info whether it’s an interference engine.

Because of all the efficiency and power issues, I’d always assume any modern engine is interfering until an authoritative reference (not some web list) says otherwise.

We didn’t get these lightweight, high-power, high-mileage, high-durability engines for free, folks. We had to trade away the thumping, fix 'em-with-a-spoon, keep running half dead dinosaurs and all their ease of repair.

In a word no. Timing belts are external to the engine block. Timing chains are internal to the engine block. Things that are internal get oil all over them constantly. Timing belts run dry (at least they are supposed to, as oil contamination can cause premature failure of the belt). Timing chains need lubrication so they are inside the engine.

External but normally hidden from view, unlike the drive belt that runs the alternator, power steering and A/C. Replacing often require a good deal of dismantling and setting the timing with the new one need a good deal of care and expertise. The timing belt or chain has a single function which is to drive the cam shaft(s) which open and close the valves at exactly the right times.

Wrong. The scheduled maintenance guide for the 2004 Highlander says to change the timing belt at 90K OR 108 months which ever comes first.