There are no codes to be had in an '89. All you can do when hooking it to a scanner is read certain real time data such as timing advance, rpm, O2 voltage.... There are no stored codes to be read.
The only problem with running a belt loose is as Rocnrol said, every time it slips it gets a bit more glazed, the more glazed it gets the more likely it is to slip. When it does slip it will be when its under high load, just when you need it most.
The bearings were chosen to be able to handle the load of a belt at proper tension. Yes, over tightening the belt will reduce their life and theoretically leaving it loose could extend it, but at the cost of the belt for really little gain to the life of the bearings. I am quite satisfied with life span of the bearings on my vehicles, as I said I only had to do the idler once on the 100,000kms that I had my XJ. I really dont think leaving the belt a bit loose would have extended it that much. Also come to think of it that bearing was far cheaper than a good quality Gatorback belt. A mute point I know....
I myself have a HUGE load on my belt when wheeling due to the electric fan I swapped in and running the winch adds a big load plus the upgraded alt, AC compressor.... it all adds up. I myself do NOT want to hear the belt squealing when I kick in the winch when out wheeling.
The ``proper tension`` is not an exact science and when I think about this thread I start to laugh inside that so much effort is being expelled on this topic, however it is the middle of February so what can you do.... 
Here is how I do it, tighten it up nice and snug but don`t go nuts on it. If it squeals tighten it a bit more.
And you are right... we techs HATE come backs. Comebacks mean I screwed up. I will tighten a new belt on the tighter side of things knowing that with a few days of driving the belt WILL stretch and be at the correct tension. I do NOT believe this causes any extra measurable wear on the bearings and I think that 99.9% of the the people out there who take their cars in to have a belt replaced will prefer this method over the hassle of bringing the car back a week later for me retighten the belt.
I replace FAR more belts than I do bearings which tells me that the bearings are handling the loads ok.
I have never replaced a belt due to glazing.
I have replaced many belts due to cracking.
I'm pretty sure increased belt tension would contribute to cracking, both by phisically stretching the belt, as well as the additional heat the belt will contend with at greater tensions.
Yes, the belts and pulleys are engineered to withstand these stresses, but they are also engineered with a finite lifespan. Changing the operating conditions can change the lifespan.
You are correct, bearings are cheap, but pulleys are not (which is what a lot of guys would use). And alternators cost a fortune. I have replaced several alternators due to bearing failure.
cLay, you said yourself you would rather err on the side of too-tight than too loose, with the logic that it will stretch to proper tension...that can't do anything good for the longterm life expectancy of the belt. Of course it's still the right choice in a shop setting, but not for me or my jeep. I would rather fine tune the belt to run at the loosest setting where it does not slip.
I will worry about what has caused me problems in the past. If you have not experienced these problems then obviously my advice on how to deal with these problems will not be suitable for you.
I have enjoyed the discussion, thanks to everyone who has contributed, I think it's time to move on.
Topic: How to save $$ on idlers, belts, accsessories etc. (Read 22056 times)