OneGuyInCA

Does anyone know if the RX300 engine is what some refer to as an "interference engine" that if the timing belt should break, pistons will collide and the engine will need to be rebuilt like in the Audi's?

Also... what is the recommended interval for changing the belt?

Lexmex

It's interference. We once made the assumption it was non-interference, but that was based on earlier versions (before 1999) of the 1mzfe engine (Camry/ES300).

That being said, normal change out occurs every 90K, but the belts have no doubt been shown to have lasted longer than that, I think we have a few documented cases of going after 150K, but I haven't to my knowledge heard of a belt breaking in an RX300.

OneGuyInCA

Thnx. That's much better than my Audi A6 which many recommend replacing between 60K and 70K. Colliding pistons on that car results in $5K engine rebuilt.

With this type of risks, I wonder why car manufactuers can't improve on the engineering to avoid this kind of potential disaster.

salimshah

If you want minimum volume (tight on compression) along with large valve opening (to ease the exhaust and inflow) the valves have to encroach on the piston possible location. As long as things work like a clockwork there is no problem.

The other part of the problem is how to keep them in sync. Chains have been used for the longest time but they are noisy in high reving engines. Belts are a good compromise, but need replacement.

It is a good compromise. No one has posted here, that their belt broke before 90K.

Salim

OneGuyInCA

The first car I drove 1991 Toyota Corolla had 30K on the odometer when my family first bought it. It got handed to me at about 90K I remember. I drove it until about 170K before I sold it.

The belt was original.

sktn77a

iTrader: (2)

Wow, LexMex, are you sure? We always thought (on this forum) that the RX300 had a non-interference engine. What changed this opinion? I had my belt changed today (see my other post) and I'm sure glad I did, if this is the case!

OneGuyInCA

Did some quick research and found this.

http://www.gates.com/downloads/downl...older=brochure

It's a link to Gates Timing Belt Guide (copy and paste the URL)

Per the guide, the '99 RX300 is an interference engine with a belt driven water pump. Recommended change interval at 90K.

btw... how much did you pay for your TB for parts and labor?

TunedRX300

Lexmex and I for a long time thought the 1mz-fe is non-interference but it turned out 1mz-fe VVT-i is interference.

salimshah

When a failure rate is to be determined, one does random sampling and typically in a defect free object, failure rate follows a bell-curve.

If it is a non-essential object, one can suggest replacement at the middle of the curve. But if you can not tolerate failure, you have to move to end of the cure 6-sigma or 12-sigma and beyond. if your belt did not fail on you for 170k great, but had it failed .. it would have cost you.

The other important fact to keep in mind is that the wear on belt is based on linear travel; which is rotations of the engine. Since cars for people do not keep track of rotations, milage is used (reasonable approximation) and the manufacturer selects a "recommended" service time around it. Other factors like age and thermal stresses also play a part. I almost forgot to mention, the belt may stretch without breaking (which is a failure too)

Salim

lexysexy

I'm new to this, so hope this goes right, According to your research, '99 Lexus RX300 is NOT an interference engine. Per the Gates Guide page 35 Part number T257- no star next to it. Can you confirm this. I have an opportunity to buy a 99 Lexus RX300 AWD 263 thou miles, very nice car with only 1 rust spot size of a golf ball on top of rear wheel fender, runs ok, might need plugs for $400 (friend of mine) but I am a tad worried whether this is an interference engine or not.

salimshah

Welcome to Club Lexus.

Before I answer your question ... how will this information help you? Are you going to wait till the belt breaks before you would make repairs/preventive-repairs? How many belt replacements would you save in the lifetime of the RX by pushing the miles out? Even if the pistons are not damaged, are you willing to take the risk of being stranded?

Belt will have almost 0% chance of failure if you replace it by 90K miles. People have waited till 120K. Some are pushing their luck.

BUT there are other things in the drive train that need to be examined at 90K intervals ,,, water-pump, idlers and tensioner.

Now the answer to your question .. RX300 has VVTi engine and most likely the valves to piston would have a clearance when the belt brakes. But at certain rpms, when the belt brakes the clearance may not exist. Even if the spacing is there, once the belt breaks it whips everything ... not a pretty picture.

Salim

NewCarGal

I have been researching for two days and see both on the RX300 as non-interference or interference. I was mad that I bought my 1999 Lexus from a non-Lexus dealership, paid $350 for a used car purchase analysis and they didn’t call for a timing belt need. Took it to my private mechanic, he said it was clicking loudly and already damaged 2 cylinders. Getting my belt changed next week. The guy who sold it to me knew it wouldn’t turn over sometimes but he thought it was the battery,

Fit1too

Not sure what he means about "clicking loudly and already damaged 2 cylinders". If that were the case I wouldn't bother with a timing belt. Like you, I have read conflicting opinions concerning the 1MZ-FE being a non-interference engine. I had my belt snap on my 99 RAV4 a few months ago and it just coasted to a stop. Had it towed to the Toyota dealer that I use and they installed a new one. The biggest thing was the hassle, it was 11 at night, at a major intersection, etc. The RAV only had 66K on it when it went, but it was 8 years old. The previous owner had it done at an independent shop and it was an off brand, not a Toyota belt.
I had Toyota do my RX a few weeks ago for piece of mind.

carguy07

Um, time for a new private mechanic.

NewCarGal

I can see already in this forum that even seasoned owners have to make decisions with imperfect information. As a rookie, I will have to do my best because I have no clue what maintenance was done on my RX300 and I don’t know much about engines. I will decide to enjoy my new wheels and read these chats and the owner’s manual asap. Putting two different mechanics on it did confuse things a bit. But I do think I will get the timing belt and water pump replaced by my local shop because they priced both at $950 including tax and labor. And tires then I will try to drive it a year. I love how it drives, best car ever so far.