+1 for Rustfarmer

Those of us living where the temps can drop well below 0 and stay there for awhile have been mixing antifreeze 50/50 (or 55/45) for forever. If we do an emergency add of water in the summer, then we check the specific gravity of the solution (with a $3 instrument) before winter comes to make sure we don't bust a block. After a few years drain it, maybe powerflush, and refill.

The pre- mixed stuff just makes it a little easier. I'm sure the Toyota tech who said use it at 100% was referring to the pre-mixed stuff.

There's nothing complicated or terribly unusual about Toyota's requirements. Just about all antifreeze now is fine for alloy and aluminum blocks/heads (not true in the '70's). Just know whether that gallon jug you bought is already mixed, or full strength - that's about the most important thing to know, and the rest takes care of itself.

 

Here is the Fluid Chart for Lexus
http://lexus.sewellparts.com/fluids.php

It looks like there was a change in 2006.

According to the above Chart, the SC430 shows:

2006-2010 uses SLLC (Super Long Life Coolant) States Pre-Diluted, DO NOT ADD WATER, right on the bottle
2002-2005 uses LLC (Long Life Coolant) Does not state to anything about not adding water on the bottle.

My 2007 and 2008 states to use 50/50 mix. Since the SLLC is 50/50 pre-diluted already one would just pour it in as it came from the bottle for years 2006-2010.

One would have to read the owner manual for the 2002-2005 to confirm if the undiluted LLC for the 2002 year is to be diluted prior to using or not. I highly suspect it should be diluted by the user.

What does the 2002 owner manual say in the Do It Yourself maintenance section?

 

It appears that the '02 SC coolant requirements in regard to using a 50/50 mix of ethylene-glycol based coolant mixed with demineralized or distilled water are no different than the requirements for 2003 through 2010 SC's. Wording direct from an online 2002 SC430 Owner's Manual:

Coolant type selection

Use of improper coolants may damage your engine cooling system. Your coolant must contain ethylene–glycol type coolant for a proper corrosion protection of your engine that contains aluminum components. We have used “Toyota Genuine Long Life Coolant” in your Lexus vehicle. In order to avoid technical problems, we strongly recommend using “Toyota Genuine Long Life Coolant” or equivalent.

In addition to preventing freezing and subsequent damage to the engine, this type of coolant will also prevent corrosion. Further supplemental inhibitors or additives are neither needed nor recommended. Read the coolant container for information on freeze protection. Follow the manufacturer’s directions for how much to mix with plain water (preferably demineralized water or distilled water). The total capacity of the cooling system is given on pages 290.

We recommend to use 50% solution for your Lexus, to provide protection down to about –35C (–31F). When it is extremely cold, to provide protection down to about –50C (–58F), 60% solution is recommended. Do not use more than 70% solution for better coolant performance.

 

I had my timing belt and water pump replaced Feb. 2012, at that time my Toyota mechanic told me to purchased coolant to filled up (I work in Toyota dealer). I told him to just get them and I will pay for them later on. I know I asked him whether the coolant needed to mix or not. He told me that they all came premixed and just pour to use. I had never heard of coolant that came premixed until then. Anyway, my point is that thru one year in Texas heat(100F plus) and cold(low 10F ) of last year till now, my gauge reads as normal as it can be, a little under half way. Members in DFW area know that we had cold weather not too long ago with over night freeze. My car took about 5 to maybe 7 minutes to warmed up which I think is normal.
I am not against mixing coolant but if my car has premixed Toyota coolant and is running fine with it, I am not going to do against it. Now, of which Toyota coolant my mechanic used, I don't know, all I was told was he used the premixed kind and I had this guy taking care of all my cars since 2007 with no issue at all. I trust him and I didn't think of checking at all.
Personally, I would just check if the coolant in hand need to be mixed or not and be done with it.

 

The concentrated coolant has has some sort of lubricate in it you can feel it between your fingers. This will help lubricate the water pump and seals.

Also I've left a small puddle on the garage floor and it will take a few days before the coolant completely evaporates.

I usually mix 50/50 the Toyota concentrate coolant with distilled / demineralised water.

 

I must be missing your point. The parts store product has lubricant in it and take a long time to evaporate also. and the 50/50 is not the concentrate.