I Put Mercon V In My Power Steering!

[Eric S.]

After looking everywhere (Bentley, owner's manual, forum search) and even interviewing a couple of techs at the BMW dealer for an answer, I got nowhere in trying to find out whether the "ATF" I'm supposed to use in the power steering system on my 1999 540 should be Mercon, Mercon V or Dexron III.

So, for my project of changing out my leaky p/s hoses, I bought a quart of Castrol Mercon V and got busy. After installing the new hoses, and running the car for a few days, all seems well, and in fact the power steering pump seems quieter than before as well.

Great, right? Weeelll, tonight I'm going through the "General Maintenance" part of my Bentley and only in THAT section on one little page does it say (in small font) that Dexron III fluid should be used!! D'OH!

So I did some research and found that some brands (Havoline) come right out and say their Mercon V also meets the Dexron III spec. Castrol's web site didn't come right out and say it, althoo their spec sheets are very similar for their Dexron III and Mercon V products. If anything, it looks like the Mercon V is maybe just a bit less viscous and a bit "lighter".

I don't see the 540's ATF system as being nearly as tough on its fluid as a transmission would. So - Am I OK to just leave it all as-is, or should I set about draining and refilling my power steering system right away? Whichizzit, whichizzit? Thanks!

[xsperf]

how big of a job is it? i think that if its not making any noise and its fine, leave it, but then again, if its not that hard to drain the fluid, then drain it anyway

[nukeduster]

Originally posted by xsperf@Apr 27 2005, 09:46 PM
how big of a job is it? i think that if its not making any noise and its fine, leave it, but then again, if its not that hard to drain the fluid, then drain it anyway

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I did that before in my 325i. I just left it in. The rack started leaking from the inner tie rods after about 3 months. I just let it all seep out over time, slowly replacing it with Redline dextron III atf fluid and it doesnt leak anymore.

Haven't had problems since.. but its definately not good.

[Eric S.]

Originally posted by nukeduster+Apr 28 2005, 12:28 PM--><div class='quotetop'>QUOTE(nukeduster @ Apr 28 2005, 12:28 PM)</div><div class='quotemain'><!--QuoteBegin-xsperf@Apr 27 2005, 09:46 PM
how big of a job is it? i think that if its not making any noise and its fine, leave it, but then again, if its not that hard to drain the fluid, then drain it anyway

[snapback]338661[/snapback]

I did that before in my 325i. I just left it in. The rack started leaking from the inner tie rods after about 3 months. I just let it all seep out over time, slowly replacing it with Redline dextron III atf fluid and it doesnt leak anymore.

Haven't had problems since.. but its definately not good.

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[/b][/quote]
Thanks for the input. I checked the technical specs at the Castrol website and the Mercon V seems to be superior to Dex-III regarding flash point and fire point, but is about 1/3 thinner (13,000 vs. 20,000 viscosity), and is a tad lighter (specific gravity of 0.85 versus 0.86 for the Dex-III. So my theory, even before I saw your note, is that leakage might be the only problem. Your story confirms that suspicion.

Since I have the V8 and thus have the old-fashioned recirc ball and don't have a steering rack like you did, my experience may be different. Either way, I'm prob going to replace the fluid in about 2 or 3 weeks. A guy on Roadfly gave me the procedure and it sounds pretty straight-forward.

Thanks again!

[Eric S.]

UPDATE: I got a reply back from Castrol corporate (via a web page inquiry) confirming that their Mercon V can "be used in applications calling for Dexron III/Mercon."

So, Mercon V trumps Dex-III. That makes me feel good that I am not harming anything in my power steering, but I still intend to do a complete p/s fluid change-out to Mobil-1 synthetic ATF in the next month or two (per the procedure offered in response to this same issue I posted on Roadfly).

B)

[nukeduster]

Originally posted by Eric S.@Apr 29 2005, 10:03 AM
UPDATE: I got a reply back from Castrol corporate (via a web page inquiry) confirming that their Mercon V can "be used in applications calling for Dexron III/Mercon."

So, Mercon V trumps Dex-III. That makes me feel good that I am not harming anything in my power steering, but I still intend to do a complete p/s fluid change-out to Mobil-1 synthetic ATF in the next month or two (per the procedure offered in response to this same issue I posted on Roadfly).

B)

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yea, its really too bad the 540 uses recirculating ball. its the only thing that turns me off by that vehicle. :/

goodluck with everything.

[sp0rky]

yeah...
The feel of the ball isn't as nice as a rack, but I still don't mind the ball because the turning radius on cars equipped with it is MUCH sharper than those equipped with a rack. My e39 528 is horrid at turning / u-turning. My e34 with ball is MUCH better. the 540s feel more like the e34. easy to park and squeeze through tight spaces

[Eric S.]

Originally posted by sp0rky@Apr 29 2005, 06:39 PM
yeah...
The feel of the ball isn't as nice as a rack, but I still don't mind the ball because the turning radius on cars equipped with it is MUCH sharper than those equipped with a rack. My e39 528 is horrid at turning / u-turning. My e34 with ball is MUCH better. the 540s feel more like the e34. easy to park and squeeze through tight spaces

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Sporky -

Interesting about the turning radius - I did not know that!

Another tidbit - my steering feels MUCH better and smoother, in addition to being quieter, since changing those hoses and putting the Mercon-V in there. Maybe the slightly lighter weight Merc fluid made the difference, or, maybe just not being perpetually-low-on-fluid-because-the-doggone-hoses-leak is paying off...