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Jim Rolando 11-19-2012 02:40 PM

Synthetic ATF in Power Steearing
It's getting about time to flush and replace the fluid in my steering at 25K. I noticed to day it is getting a little dark. Does anyone have any thoughts pro or con about replacing it with synthetic ATF?

Dr._Zoidberg 11-19-2012 03:00 PM

I'm pretty sure the standard thing for most people here is to replace it with one of the universal ATFs out there, and I've been using Mobil 1 for years now and it has always worked the same. I don't see any cons to using synthetic since it is well proven that synthetic is better in every way except for price, and with the amount used in the power steering it won't be very expensive either way. If you suck up what is in the reservoir with a turkey baster or fluid pump then refill every time you change the oil you won't have to worry about the P/S fluid getting too old.

the540wgn 11-19-2012 03:56 PM

I just used the standard Dex/Merc it was cheap..
I think the only con of a synthetic would be price

FLE39 11-19-2012 06:51 PM

Price is probably the only real bad thing. But it's a good idea to use syn. Cleaner and won't break down as quick. I'm probably going to do M1 or something alike. I know in my 335i, hell it needs the Syn ps fluid. Sheit turned dark brown by 40k. But it take the fancy german stuff in a metal can, no options there.

Edit: Dex VI should work where any prevoius Dex II or Dex III is called for. Backwards compatible. And I believe this is GM's most updated ATF, which is syn or part syn. I'm probably going to go that route. When our E39's were made, Dex III was current. VI wasn't even a thought back then. So yes, something like the M1 ATF or Dex VI Castrol would be a good thing at lest for keeping it clean and high temps.

Edit 2: Some good GM info regarding the Dex VI as ps fluid in a dex III system. GM started using it in 2012. They seem to be worried about a seal squeak when converting sytems over. Not sure if that's an issue with a BMW b/c GM makes every plastic rubber out of road trash. But good read none the less.

Bob is the oil guy forums have good info. I'm going either Dec VI or M1. I wouldn't mind going to Pentois CH11S like my 335i, but that maybe to much of a change. I'm going to disconnect the resv return hose and make sure I get a 100 Flush.

Edit 3: looks like Dex III has (had) a certain visc and M1 ATF is for that application. Mobil makes a specific ATF for Dex VI appliations. So Dex III and Dex VI are different in tems of visc. Gm is ok with you running the newer thinner better fluid in the older transmissions. But M1 ATF is NOT for Dex VI applications. BMW's CHF 11S is basically their own european version of going to Dex VI p/s fluid. But even thinner. So from thick to thin; Dex III (M1 ATF), Dex VI, CHF11S.

40*C Visc, 100*C Visc:

Mobil 1 ATF (Dex III): 36.3, 7.4
Mobil Dex VI: 29.5, 5.83 [Castrol Dex VI is 30.0, 6.1] Dex VI is a "SYN BLEND" by spec I think.
CHF 11S: 18.7, 6.0

I'm probly one of the only people out there that wants to switch from cheap ATF to expensive CHF 11S!! But I'm not sure how that's going to work. I know you can't mix them... but even after a flush I question the seals and that a extreme Viscocity change. I'm going to play it safe and go middle of the road with Dex VI. See how that does first. Then "maybe" flush out to CHF 11S.

DHoang 11-20-2012 07:15 AM

FLE going way overboard w/ this ATF specification for our p/s systems.
a p/s system don't care whether ATF is dextron 3,4,5,etc...or whether
its type F, OR whether it's dino or group5 synthetic. All it cares about is whether it's a hydraulic fluid and whether it's within a range of viscosity to not exceed or not provide a set psi when the p/s pump's under operation.

You can use walmart atf and it will hold up everybit as well as the top of the line ATF like Redline, Amsoil, Pentosin, etc.... b/c in a p/s application, there is hardly any heat generated....nothing even close to the type of heat generated inside an auto trans. So ATF in a p/s do not break down. it only gets dirty.

The most important thing, therefore. is to keep the ATF fluid clean. Thus, using walmart ATF, and changing it out every 20k miles is alot better than using Redline/Amsoil/Pentosin ATF and changing it out only when required (such as when there's a leak or a hose replacement).

FLE39 11-20-2012 07:47 AM

^ I can agree to that. But on my 335i the p/s fluid is cooked. And it's CHF 11S. Ask the track guys. Even mine was shot. I've decided to just run some Dex VI Castrol and change it often. I'm not paying $10+/qt for M1 ATF. the Castrol stuff is like $6/qt.

rdorman 11-20-2012 10:13 AM

Castrol Import Multi-Vehicle is what I use.

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