Would you consider doing a flush? It is pretty easy and quick and you get all the old fluid out in one go.

As for the fluid, It should say in your owners manual if you still have it exactly what fluid to use. My 2005 lexus states Dex II and III as well. I have heard the Toyota mechanic say to use regular power steering fluid instead because the Trans fluid does not have the same additives, but then hear from owners that put PS fluid in the toyota end up replacing their PS systems a couple times.

To flush, it is very simple.
Jack the front of the car up, You only need it up to where the front tires are not touching the ground, just an inch or so.
You will need maybe 5 or 6 feet of clear tubing
You detach the little hose off of the PS res, the return hose, this brings fluid from the PS system to the res, you then plug the hole in the Res with something so it will not leak, I use a 2 inch piece of the clear tubing, slide it over the nipple on the res and bend the end over and zip tie it down to create a plug. Now attach your clear tubing to the return hose you pulled off the res. You may need some kind of device such as this to attach the two hoses together. Now run the other end of the clear tube down into some kind of container to drain into.
Once you are all set up. (make sure your parking brake is set before you jack up the front end). use your turkey baster to pull out the old fluid from the res then refill almost to the top with fresh fluid. watch the hose and your res (hose to see the color of the fluid and res to make sure it does not get too low), Turn your key to unlock your steering (do not start car) and turn your steering wheel all the way left, then right a couple times, then top off the res and repeat until you see the fluid going into the clear tube become clear and pink like the new fluid, you can give a couple more turns to make sure and that is it. Turn the car off, let it back down, replace your return hose and adjust the fluid level in the res. Your system is completely flushed.

Here is a video, This guys way is even easier, he does not add any clear tubing, just pulls off the return hose and places the end in a bottle to collect the fluid. This is a very simple job, and probably faster than and for sure more effective than the turkey baster meathod.
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Thanks. The reservoir says Dex II, so that is clear enough. I'll look into the flush option and try to find time to do it. The Toyota Ps fluid is VERY expensive here.

What would be the difference if I used Dex II vs Dex III or vice-versa?

 

Suck out old fluid with the turkey baster, fill with new fluid, start engine, turn steering wheel to full lock both directions 2-3 times. Repeat until removed fluid looks like the new fluid.

 

Just checking what is the best fluid to use. Dex II and III have been updated and whilst the newer fluids are backwards compatible I think they might be synthetic vs Dex II which is mineral. I'm thinking it would be best to get Dex II and use that, keeping with original spec?

 

That is what I would do.

 

What volume of new fluid will I need to flush out the old?

 

Depending on the total system volume (which I don't think is ever listed), at minimum two single quart bottles. But if the fluid is really old, you may need upwards of 3 or 4 just to be safe.

 

I was going to get 2l of Motul Dexron II D ATF fluid (which is red) due to it being a good price. I know that Motul products are good. Is the colour just a dye or has other significance? Other option (price) would be Liqui Moly 1145 3100 Steering Gear Oil which is also Dexron II D (I think this is green).

 

The 1145 looks like a mineral based oil of an obsolete GM spec (anything before Dexron VI). Many members here just use Valvoline Maxlife in the PS too, which is a Dexron VI spec and fully synthetic too.

You might consider Liqui-Moly 1200, which is a fully synthetic Dexron IIIh instead, but the 1145 should be fine too.

Top Tec ATF 1200

Fully synthetic automatic transmission fluid with modern additive technology provides high thermal stability, excellent wear protection and correct friction behavior. Excellent low temperature behavior. Compatible with most common seal materials.

www.liqui-moly.com

 

Cannot find Valvoline in UK. I have found some genuine Toyota DEXRON III ‘Power Steering Fluid’ cheaper than LM so will go for that.