While canvassing the LS430 side, I came across a posting relating to cold start-up noise in hydraulic power steering pump at 0 F.
While the noise diminished after warm-up, it made me wonder whether anyone had replaced mineral oil based "DEX/MERC III with a synthetic equivalent to improve P.S. pump performance/efficiency/life while reducing noise and wear at start up...especially lower temperatures.

My 1999 LS400 has a brand new Lexus pump and it audibly struggled at start-up pumping honey-like mineral oil based ATF at 0 C..

Valvoline offers a synthetic version of it's DEX/MERC III ; MAX LIFE FULL SYNTHETIC DEX/MERC LV.

Product comparison information is attached and following, however this information does not explain synthetic blend's fitness for our power steering systems...

Canvassing online, the worst I find is synthetic fluid is more prone to leak...not sure this would be the case at all...unless seals were worn out..


Located this DEX/MERC III chart online (unbranded) for mineral based ATF depicting viscosity vs temperature...it is apparent that viscosity increases exponentially below 30 F..
Valvoline mineral based DEX/MERC ATF as recommend for LS400 P.S. systems.
Valvoline synthetic version of its' DEX/MERC ATF....
The synthetic back label suggests it is a substitute for Toyota Type IV... If so why couldn't we simply use Toyota Type IV in our power steering systems?....and why didn't Toyota do so in the first place??

Valvoline Mineral Oil based DEX/MERC III:
Viscosity @ 100°C, cSt 7.1
Viscosity @ 40°C, cSt 34.5
Viscosity Index 174
Specific Gravity @ 60°F 0.859
Density( lbs/gal) 7.17
Brookfield Viscosity @ -40°C, cP 15,000
Pour Point, °C (max) -42


Valvoline MAXLIFE DEX/MERC LV

Viscosity @ 100°C, cSt 5.91
Viscosity @ 40°C, cSt 28.82
Viscosity Index 156
Specific Gravity @ 60°F 0.843
Pour Point, °C, -48
Brookfield Viscosity @ -40°C, cP 10200
Flash Point, COC, °C 202
ASTM Color 7
Appearance

I observe on the back thst Valvoline MAXLIFE holds itself out to be a substitute for Toyota Type IV transmission fluid....

If this is the case, then the question is why not use instead Type IV Toyota synthetic transmission fluid in our power steering pump....or, moreover....why didn't Toyota simply use Type IV synthetic transmission fluid in the power steering pump in the first place...

 

YODA
When you installed your new PS pump did you use an air control valve or did you plug it? I drive a 99 as well and I'm replacing my PS pump tomorrow. I have a new Lexus pump and I plugged the orifice with a bolt and some Permatex 54540 pneumatic/hydraulic grade thread sealant.

 

I brought this up with a Master Tech sometime back and he shrugged at it. He commented that Mobil 1 ATF is his suggested synthetic fluid and that this has done well in the pumps he's serviced. Granted this is So. Cal so the temps aren't like those in northern regions. In those examples I'd select the Max Life. Ours has had Mobil 1 ATF in the reservoir for some 130K miles. I do the turkey baster routine every fall. The coolest weather ours has seen is just below 16F.

 

I reused the original air control valve.

At some point I will replace with a new one as preventative maintenance but would rather everyone use a new OEM pymp and plug the hole than use an aftermarket rebuild..

Right now attempting to determine pro and con using synthetic power steering fluid in an LS400.

If I read correctly, Valvoline siggests it is ok to mix their synthetic with mineral based ATF...

Also attempting an answer whether Toyota Type IV synthetic transmission fluid will work.. (As Valvoline suggests their synthetic can be substituted for Toyota Type IV )

 

Two years ago, my OEM pump went out on my 97 LS400 so I went w/ the lifetime warranty aftermarket pump purchased at Autozone. I've flushed the system & used the Valvoline Maxlife. Recently, the aftermarket re-manufactured pump started to leak after only 20K miles so I went back to Autozone, got the replacement, installed it only to find out it was defective. The 3rd one is working fine now so I'm not sure if the premature failure of the 1st aftermarket pump has anything to do w/ the Valvoline Maxlife or the re-manufactured pump itself.

 

Not a fan of AutoZone rebuilt anything....
The problem with rebuilt P.S. pumps is the rebuilder only replaces a few bearings and o-rings...and if the customer has a problem down the road, then they replace part with same rebuilt product..that failed..who knows whether care was used extracting the pulley or if it was wrenched out by the avid do-it-yourselfer.

Moreover, the real problem with rebuilds is you have no idea what components have been replaced....and with god knows what brand or origin parts.

If the rebuild houses and their illustrious supply chain partners were required to disclose this information, then the customer could make an informed decision...that opportunity clearly does not currently exist.

There was a time when aftermarket parts were an improvement over OEM...that is clearly not the case with most anything for Lexus.

The aftermarket P.S. pump imbroglio has been played out across these forums countless times....so the fact that you had used a particular fluid in your P.S. system cannot be used as a control..a new pump would be a different story.

Purchase a new LEXUS pump...P.M. me if you require a better price. Exploded Lexus parts diagram of 1998 LS400 P.S. pump internals... Lexus shop manual and parts list outlines the individual.pump vanes are tolerance specific and fitted by P.N....similar to valve shims..It is highly unlikely the rebuilder gets it right...never mind the quality of bearings, o-rings, shaft resizing (shaft surface worn where seal/oring mates) internal pump housing, polishing, replating, etc.

 

Yeah, if the newly installed re-manufactured pump crapped out prematurely again, I'll definitely go w/ back to the OEM pump.

 

Purchased $20 gallon of Valvoline synthetic ATF and employed turkey baster extraction method to remove mineral oil ATF... Two quarts upfront then two quarts more after a few days driving.

Am comfortable with some mineral oil in the mix as Valvoline claims their synthetic is compatible.

To my touch the steering feels barely, but discernibly lighter at idle and in parallel parking situations with fully warmed engine...

At cold start up the P.S. pump is less audible (new OEM Lexus pump) and steering is appreciably lighter, suggesting the synthetic blend benefits driver and the steering system.

 

Autozone, O'Reilly and the local parts houses have slim pickins' for pumps - either Cardone, ATSCO or BBB. The first two are known for spotty quality. There's also a flood of new Chinese pumps as well these days. Many times, a "reman" pump will simply have its seals replaced - but who knows what shape the campack/rotor and vane assembly is in? The pumps on these cars isn't too much of an ordeal to reseal and inspect, but finding a decent seal kit outside of the dealer is a pain.

Maxlife fluid does work fine, it might be thinner than DexIII fluids, but it can help with cold weather performance and it does last longer - M1 or Red Line is good too but also more expensive and PAO/ester fluids don't play nice with certain seals. I doubt many power steering systems care about viscometrics, as long as their seals don't weep.

 

I can not find the PM button. I am looking for a OEM New 92 LS 400 Pump.