Curious, I changed my belt yesterday with 160K on my 98 S70. I went 85K on this belt and when I removed it, it looked in as good of condition as my new belt. No cracks or anything. Is the reason for the change due to internal breakdown of the belt? or is it just a genearl maintenance thing. I wonder if we could get away with periodic inspections of the belt by removing the cover and looking for cracks, etc.

Anybody ever replace the belt and see their old one in bad shape? Maybe it is just internal breakdown and the thing just snaps one day?

A good engineer (and I hope Volvo has some) would decide this interval based on a statistical cost-benefit analysis after some testing, and update the decision based on real world reported experience. There are many factors which differ according to the particular car, belt, ambient air pollutants, severity of use, etc. - and most of these are invisible or unmeasurable. Hence any recommendation based on direct analysis of the belt is likely to be very uncertain.

If you want to drive longer on the belt, you know with certainty that you will spend proportionately less money on belt replacements over the life of your car, the longer you go. But at some point which you can't know, the likelihood of failure will go up severely - due as you say to internal damage or some other factor. Unless you are willing to take lots of risk you won't save much.

I know of a couple of incidents where a timing belt snapped way ahead of time (<50K miles). It's rare but possible.

Many other situations work this way. For example you're required to get an annual or triennial rabies booster for your dog. Certainly the vaccine will not stop working suddenly on day 366 (or 1099) or any other known day. It's more like a kind of insurance against both the loss of your dog and the spread of the disease.

Strange, is it not? The same belt is good for 70K or 100K, depending on the model year/ tensioner. The belt should be good for 100K miles, regardless of model year, but the tensioner for pre 1999 puts too much wear on the belt. The hydraulic tensioner needs to be replaced every other belt change, while it is recomemded that the manual tensioner be replaced at every 105K change.
If the belt shows signs of age, cracking or loosing teeth, it is already too old and needed to be changed a few miles back. Remember, miles + time is the real criteria, not just miles.

Klaus

My '98 V70 GLT is a late build of 7/98 and came with a mechanical tensioner.

I replaced the t-belt at 100k miles (following the '99 105k interval schedule), and the t-belt was beginning to show signs of wear at 100k miles. Mechanical tensioners are gentler on the t-belt than the hydraulic ones, thus the longer interval.

--
'88 240, '92 745, '98 v70 -John, Tampa Bay

interesting...what kind of wear?

Mine was the hydraulic tensioner.