I was sitting still on the freeway, the outside air temperature indicated 106, the front and rear air were blowing hard, stereo was on and 2 cell phones were charging. I could see waves of heat coming up from the the pavement. We sat 10 minutes. I put it back into drive for the 3rd time and pressed the accelerator to move forward, about 3 seconds later the vents started blowing noticeably harder. At first I thought it was a coincidence, when it happened several more times I wondered if my alternator was going out? With a little research I found that increased heat decreased output some say by as much as 30% at idle. I did not find anything indicating age degrades output. Further digging and I found that some models prior to 2003 had 100 amp alternators and my 03 had a 130 amp. But why did they add 30 full amps? A little more digging and I found that idle amperage output is substantially lower than full rated output - see chart. I could not find any published specs on idle output from Toyota and less on the effects of heat. In addition the output curve is not linear, in other words a 50 rpm decrease might be just enough on a hot day to drop output below what is required. Apparently Toyota engineering had decided to increase the idle amps at some point and the best way (perhaps only way) is to increase the total output. I shopped around and decided to try a DC power engineering upgraded to 180 amps. They build new alternators from Denso parts, I am not a fan of reman alternators for an over the road vehicle, I put them on all my stay around town vehicles. The installation required removing the power steering pump bolts and suspending it high enough to keep it out of the way. I did have to twist and turn the unit to get by the pressed hoses. The new alternator came with a slightly smaller pulley, by my calculations it would spin about 12% faster than the previous one. This will I am sure wear faster, however not by much and I would rather not drain my battery sitting in the heat. I am thinking that 100K miles on the old alternator equals 112k on the new. No big deal, these Denso units last forever according to my local rebuild shop. To my surprise the local shop knew about DC power and said I bought a fine unit. The important thing for me is to replace it long before it stops working since I am using the LX for road trips over 90% of the time. I measured the diameter of the old and new unit, old pulley is 5.6 cm and new is 5 cm. Not much until you calculate the difference with the 14 cm main pulley. So the combination of a little more speed and a larger peak output gets me where I think I should have been in the first place. Interesting that the Tundra gets the 150 amp version. Here are the amp draws from some of my testing while I was trying to figure this out. Hope this helps someone out there.
Idle with everything off 7.5 amps
Engine idle up from 2k to 4K - 3 amps
AHC 6.7 amps
Front Fan on MAX 8.7 amps
Rear Fan on MAX 4.9 amps
AC compressor .8 amps
stereo 3/4 turned up(I listen at this level a lot) 5.5 amps
DVD .5 amps
Idle with everything off 7.5 amps
Engine idle up from 2k to 4K - 3 amps
AHC 6.7 amps
Front Fan on MAX 8.7 amps
Rear Fan on MAX 4.9 amps
AC compressor .8 amps
stereo 3/4 turned up(I listen at this level a lot) 5.5 amps
DVD .5 amps
