Multiple alternator failures. Causes?

With the limited info you provide here are some suggestions:
1. Dead batteries can kill some alternators on startup.
2. Maybe the alternator was bad once and then was rebuilt bad 2 more times.
3. A ground issue causing the premature failure.

I know nothing about a Lexus and these are general suggestions for the problem.

 

Things I have learned most often can go bad on an alternator.

1) Brushes
2) Slip ring
3) Voltage regulator
4) Voltage rectifier

Not that your parents are running a high power competition sound system, but an over loaded alternator can get killed from devices that require more power than the alternator can produce.

 

Lexus SC 400 Faults

Lexus SC400, then it is important that you review the official NHTSA auto recall reports to find problems and defects in the Motor

motortrend.com/used_cars/11/lexus/sc400/recalls/

 

All these suggestions are spot on; I'm a fan of the 1UZ engine in the SC400 as they're a popular motor to hotrod and I've built several of them for a supercharged application.

The alternator does live right under the P/S pump so it can and does fail in the same way it fails in our 550's, where it lives right under the A/C compressor.

Mind you, there's nothing inherently defective with these alternators - they're very high quality Denso units, similar to, and perhaps interchangeable with those on our FCars, but bad things do happen to them. Blown diode bridges are a fairly common failure mode, and can be caused by the P/S fluid leaking into them or overcurrent on startup due to a dead battery.

If it were me, I'd tear the next one down and look for what actually failed, then go after the root cause rather than just slapping another rebuilt unit on the engine. If the car sits for month(s) at a time, I'd encourage your parents to invest in a CTek or other trickle charger. With their frequency of driving the car, it's amazing they haven't had to replace the battery multiple times too.

 

Next time:

Recharge the battery all the way up to full before starting it after the car has sit for several weeks.

When the alternator has to power both the car and recharge the battery at the same time it is being overloaded. A daily driven car (like the 400 was designed to be) will seldom be in a just barely startable condition, so the alternator lives a long life. But when you have to rechage at the same time as supplying the car with power, the alternator can only withstand this a handful of times.

 

An overtightened alternator belt will burn up the bearings fast and is a common repair mistake.

 

The Lexus motors have "real" auto tensioners for both the serp and the timing belts. No manual tensioning required or even possible. Cheap, effective and they work like a charm. We should be so fortunate with our FCars. Here's the front view of the 1UZ engine in his parents' SC400
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Hi, I have a 2006 Mazda MPV.
My wife and I drive it once a month to orange county or San Diego to do shopping.
My wife starts the van once a week and let's it idle for about 15 min. or so.
The van has about 17,000 on the clock.
After 6 years it has the same battery and the same alternator.
This method works just fine for our car.
No problems, no issues.
Maybe this approach will work for your mom and dad.
Good luck.

 

+1. As suggested previously, a battery tender would probably be helpful. I full testing of the electrical system, as well as a load test of the battery is in order. Also, the quality of the rebuilt altenators can be in question as well. If they have cheap parts (voltage regulator most commonly) they can fail an untimely death.

 

Perhaps it's time for them to find a different mechanic?