Since the Blackstone analysis of both fluids are so similar, I'm not sure 1 point is that relevant. Anyway, lines showed up yesterday, so I will attempt to get them installed this weekend.

 

Hi WinterJag,

I know I sound pedantic on this subject, but according to the MSDS for Castrol Import Multi-Vehicle ATF, its kinematic viscosity at 40C is 35.57 mm2/s, or nearly 33% "thicker" than Shell M-1375.4/Lifeguard 6. The spec for LG6 is just 26.8 mm2/s, which is among the lowest viscosities of all commonly-available transmission fluids. I'm not sure how Castrol can get away with claiming their fluid "meets the right specs" when its viscosity is 33% higher than "the right spec."

Here's the Castrol MSDS:

http://msdspds.castrol.com/ussds/amersdsf.nsf/Files/9A4E918EE19C88CE80257D98000EEF5E/$File/BP%20GHS%20US%20SDS%20-%20US%20US-Lubes%20Americas-Castrol%20%28Wayne%2C%20NJ%20US%29467634-US12English%20%28US%29.pdf

When ZF first announced the 6HP26 in 2000, they stated that the new transmission was designed to be lighter and more fuel efficient compared to the 5-speed boxes it replaced, and that it was designed with "minimal tolerances," or the smallest possible clearances between moving parts. Using a fluid that is less flowable than specified by ZF could increase internal resistances and undermine the improved fuel economy the transmission was designed to promote. Even worse, it could lead to elevated internal pressures and temperatures and pose a risk of transmission damage over the long-term.

This is a good example of why I've become skeptical of the claims of third-party fluid makers/ marketers regarding the compatibility of their products in my Jags.

Cheers,

Don

 

We've been through this all before. Mercon SP's viscocities are within 2% of LG6's, other's are way out. It's all in the file I attached to this post

 

Don B

Well, it was supposed to meet the right specs! lol

Either way, as you can see, it's been in there for a long time with absolutely no ill effects, so it's obviously working. I don't know how much difference that 33% thicker really makes under normal driving conditions. Another thing I think has to be considered is the climate in which I live. These transmissions have to be able to work in temps from +50C to -50C, so I bet they can handle a wide range of viscosity (right or wrong, I would base that on my experience). While I have never measured it, I would bet there are times when my tranny fluid never gets above say 10 or 20 C if the car is on a short trip at -40C (yes, I have actually maxed out our external temp sensors, they only go to -40C). On the flip side, just the other week it was almost +40C. Another consideration is the age/mileage on the car. I bet with over 250,000kms on the clock, any changes in the fluid specs won't cause any more issues than the normal wear in the tranny. But this is just based on my thinking, which has been known to be a little crazy sometimes!

Now, when I did this the Castrol I used said in the spec sheets it met the shell M-1375.4 requirements, HOWEVER, that was the first time I used it years ago. When I changed my car last year, I never bothered to check the specs again, and I had noticed the back label had changed on the bottle. Maybe the fluid composition was altered or something since the first time I used it. Either way, it's in there, it's working fine. I'm not going to rush out and change out all my fluid now. What I will probably do now, based on this info, is use different stuff when I do the next drain and refill on the cars (wife's is due for it this fall).

 

One other point to add to this, is that when I was researching whether Mercon SP was an alternative (not just for me, but all of us), was going through the archives of all the other car brand forums that also used the same ZF unit.

As you can imagine, this conversation has been had on all those forums multiple times. However, I went a step further and did extensive site searches for any evidence that anyone who had switched to Mercon SP ever suffered any ill effects. I couldn't find a single instance.

If you waste as much time as I did, you'll estimate that hundreds of people, if not thousands, have used Mercon SP in place of LG6 or the car maker labeled version. Logically, if there was *any* issue with the switch, it would have been reported by now.