Is there a misnomer in synthetic ATF and brake fluids (Vice synthetic motor oil)? - PeachParts Mercedes-Benz Forum

Carrameow · #1 05-08-2006, 12:30 PM

Is there a misnomer in synthetic ATF and brake fluids (Vice synthetic motor oil)? Is everyone hopping on the Synthetic bandwagon after Mobil One pulled off a big Coup by being made the designated motor oil for the 2000 Corvettes and a number of other expensive sports cars?

Synthetic motor oil makes sense when molecules can be custom tailored to resist huge frictional loads and shear stresses and heat in an engine. Furthermore filtration absorbs a huge degree of dirt and grit and material degradation of seals, gaskets, and piston rings, etc.

But in Automatic Transmissions fluids wear a lot more not to frictional or shear stress; instead their loading is more Hydraulic and caused by rapidly varying heat loading. Here does Synthetic stiil mean the same? As the fluids age during decomposition, they become more acidic and damage orings and seals and other parts.

My feeling is somepeople may be putting synthetic ATF and brake fluid in there thinking its service life or interval may be doubled. I would still be nervous of trusting my ATF after 15K miles...

Is this true? I'm not a chemist.

Hatterasguy · #2 05-08-2006, 03:12 PM

Synthetic seems to make the trans shift better. I don't know about extending service life. I don't even remember what MB specs for my car, 30k miles I think.

pawoSD · #3 05-08-2006, 03:17 PM

I've settled on doing tranny fluid changes every 17-20k or so, about once a year to year and a half, with full synthetic. 7qts of Mobil 1 + a filter/gasket kit is only about $65 (so like $50 a year), not bad at all when its aiding the lifespan of the tranny. Plus I am obsessed with maintenance so it helps my addiction.

In fact....I'm about to go outside very shortly and vacuum out the whole car.

H-townbenzoboy · #4 05-08-2006, 03:19 PM

I've noticed the smooth shifts with synthetic ATF too. The correct AT service intervals is to replace the fluid and filter every 30K miles. In harsh driving conditions, it's recommended to change the fluid only at half that interval.

Hatterasguy · #5 05-08-2006, 03:26 PM

Quote:

Originally Posted by pawoSD

In fact....I'm about to go outside very shortly and vacuum out the whole car.

Oh my your as bad as I am!

Lets see at the rate I drive the SDL 15k miles will be every three years, 30k every six. So maybe I'll stick to the 15k-20k range.

vstech · #6 05-08-2006, 03:29 PM

Quote:

Originally Posted by H-townbenzoboy

I've noticed the smooth shifts with synthetic ATF too. The correct AT service intervals is to replace the fluid and filter every 30K miles. In harsh driving conditions, it's recommended to change the fluid only at half that interval.

MY CHEVY ASTRO stupid caps key. sorry. anyway, usually goes about 160-200K between transmission changes, is this likely to go further if I change fluid and filter? I currently have 165k ON MY (ARRGH!!) 2000 astro, and 496K on my 87 astro. I suppose I could follow this schedule on the tranny and see if it improves longevity. my trans shop said it may improve longevity like 5% or so. not really worth it in my Opinion. but hey, if the MB trannys can go 450K or more with average maintenance, maybe it is worth it... I just replaced/rebuilt the tranny in my SD, so in 20K or so I will service it and continue this schedule and report back in, oh, 20 years and see if it made any differance.
John

pdxwaker · #7 05-08-2006, 04:19 PM

From what I know synthetic brake fluid has a higher boiling point... this can definitely be considered an improvement over dyno brake fluid.

ConnClark · #8 05-08-2006, 04:35 PM

Quote:

Originally Posted by pdxwaker

From what I know synthetic brake fluid has a higher boiling point... this can definitely be considered an improvement over dyno brake fluid.

DOT5 is DOT5.

Ken300D · #9 05-08-2006, 04:48 PM

Synthetic ATF is definitely a better product. It lubricates better, cleans better and works better when cold. It has actually fixed transmission shift problems for me, probably issues that had their root in gummed up valve body assemblies.

But don't vary the maintenance interval. Yes, it is expensive to change with Mobil 1 ATF.

On the other hand, how expensive and time consuming is a whole transmission rebuild?

Ken300D

Wasuchi · #10 05-08-2006, 05:07 PM

Synthetic ATF handles a lot more heat before it breaks down. The Allison 6 speed in my big truck specifies 15k intervals with dino ATF and 75k with synthetic ATF. At 75k you sample it and replace if needed otherwise you go another 25k and sample again. I'm not going to go 75k on my car but it's right at 50k (due for a change) with synthetic and still looks great unlike dino ATF at 25k.

ConnClark · #11 05-08-2006, 05:09 PM

I have seen many of the claimed beneifts of changing to synthetic transmission fluid by just changing the filter and using good old Dexron III. I'm not buying into the hype until I see a same day test on the same transmission that shows measurable differences.

pdxwaker · #12 05-08-2006, 05:57 PM

Quote:

Originally Posted by ConnClark

DOT5 is DOT5.

Well... DOT5 meets (or exceeds) DOT5 spec's... so DOT5 is DOT5 but it can be better...

From Valvoline's site on their Dot3/Dot4 synthetic: "dry-boiling point up to 500°F" (this is ~260C... I think the DOT4 spec is 230C)

perhaps you should have said "DOT4 is DOT4" but I'm sure that's another thread ;-)

t walgamuth · #13 05-08-2006, 08:27 PM

dot 5 is silicone. i dont recommend it for benzes with disc brakes. it is fine with the old drum braked car imho, though, even superior.

tom w

Ara T. · #14 05-08-2006, 08:54 PM

And then there is DOT 5.1 which is like DOT3 and DOT4 except higher boiling point and lower moisture absorption.

pawoSD · #15 05-08-2006, 10:11 PM

Quote:

Originally Posted by ConnClark

I have seen many of the claimed beneifts of changing to synthetic transmission fluid by just changing the filter and using good old Dexron III. I'm not buying into the hype until I see a same day test on the same transmission that shows measurable differences.

It did on my car! Way smoother shifts and quieter operation, plus it shifts just as well at 5F as it does at 75F, which around here is a great bonus. Then you add in the fact that it does clean better and resists a lot more heat, sounds great to me! (especially since I'll be adding a trailer hitch pretty soon)