Thom1

Some young guys at the local parts shop said that it was bad to go back to conventional oil once I have used synthetic ATF. Any opinions?

A 928 expert that deals with these problems a lot, ruined his automatic transmission with synthetic fluid. He said that he has seen several instances of seal failure in 928s due to synthetics. That can cost $4-8K. I am planning to get my synthetic fluid out of there next week. However, the Porsche certified mechanic I am working with, and I have had no problems with our transmissions running Mobile 1. He is sold on synthetics. Mobile 1 has been in my a/t for 10 months.
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Greg86andahalf

Thom,

Steve Cattaneo is the resident expert on Porsche M-B transmissons. You should email him direct if he doesn't see and respond to this thread. Don't do anything untill he gives you his opinion.

Greg

Thom1

Thanks Greg,

I sent Steve an email. Controversy abounds on this subject. I do not ever want to pull the transmission again.

Any other experience or opinions Sharks?
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Max

A little trivia no one ever needs to know:

The trans oil was originaly made from sperm whail fat.

dr bob

Opinions and some experiences vary on the use of synthetic ATF. Like you, I switched to Mobil-1 synthetic ATF with no negatives and some driveability positives. This was done at the first scheduled ATF change on my '89 at 25k. I plan to use Mobil-1 again at the next change, due any day now.

Meanwhile, Rich Andrade in Phoenix reported some problems when he switched. He ended up replacing the gearbox at the dealer after they and several other experts couldn't identify a no-shift problem.


Back to your original question-- You shouldn't have any problems switching back to dino dexron.


Many trans problems are caused by dirt or scum that gets loose in the valve body and servos. U.S motorists, as a class, tend not to worry about the automatic trans until it has a problem. Then it's off to get the fluid changed, hoping that it will somehow fix whatever is wrong. I know that Rich has his cars serviced religiously, and in fact has a revolving account with his service shop thanks to the three 928's in the garage. So use whatever fluid you feel comfortable with, and change it regularly.


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Jerry 87 928S4

In a Porsche Technical bulletin they basically said they went to Syn oil in 1993 due to the properties which they said are:

It stays thicker in hot weather and thinner in cold weather than dino oil.

Some say this leads to leaks due to smaller molecules but as already stated - the discussion continues.

chris928

The various manufactures have tests that will qualify a lubricant for use in their product. Most synthetics pass these tests with flying colors.

It's difficult to understand how a lubricant that has better viscosity characteristics and lowers friction could cause a mechanical failure.

Thom1

Thanks everyone for the informative responses! I hardly ever make a major move anymore without the counsel of the community. I have wasted too much money on this car already due to my ignorance, and ignorant mechanics. Fortunately ignorance can be cured.

The catastrophic failures that have hit other 928 owners too often for comfort seem to be due to seal leaks. If the fluid gets by the old seals, and leaks to a fatal level, that is all she wrote. I am encouraged to hear opinions that synthetics do not weaken seals. Their smaller molecular structures just have been known to let the fluid slip by the seals. Here is where this becomes really important to the 928 owner. I turned my key today to find no ATF Fluid Level Warning Light! Silly me… I would naturally expect to see that warning system. Do you later model guys have that? Why would Porsche neglect this? …OK, the owner’s manual says to bring the car into the dealership for service if the ATF leaks. That seems like a pretty strange approach to ATF level monitoring and service… no dipstick... really inconvenient to read… no warning system. Forgive me for ranting. But that does bug me. Maybe the fatalities did not monitor the leaks. Don’t get me wrong. I pay attention. I have changed the fluid twice, and filter once so far. I check the level often. I look for fluid on the carport floor all the time.

I have also heard something about the synthetics causing contaminants to be washed into the valve body. Has anyone heard of this? Could the new fluid act as a detergent, or agent for congealing or precipitation of solids? I noticed something strange about a hesitation shifting into drive from reverse right after I put synthetic in. That has gone away now.

I will change 4 sealing rings and a gasket for the torque converter (tc), and transmission oil pump, 2 tc bearings, tc drain plug seal, transmission filter, and transmission oil pan seal. Should that be enough to cover any seal issues? (I am swapping out the torque tube. Otherwise my tc leak is too slight to justify service.)

With the satisfactory performance of synthetic ATF for 10 months, and positive opinions from this group, I am now considering sticking with Mobil-1 ATF.

Any more opinions, or answers to above questions?

Thanks again for the healthy discussion.
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Mike Schmidt

I've had the synthetic vs dinosaur discussion with a local Porsche owner, who is an engineer for a major automotive seal manufacturer. According to him, synthetics will not weaken or deteriorate seals. The reason that some old seals will leak more with the synthetic than they did with the conventional stuff, is because the synthetic doesn't swell the seals. The conventional petroleum oil causes the material that older seals were made from to swell. As the seals become older and less flexible, the swelling caused by the conventional oils helps them to seal. The guy said that synthetics were definitely better for the mechanical components, but were harder to seal effectively because old, worn, or slightly less than perfect seals don't get the help of the swelling conventional oil provides. Modern seals are made from different materials, and to higher standards, than the older ones for some of these reasons.

The automatic transmission fluid level is kind of a pain to check on a 928. Many owners probably never checked it, and didn't pay much attention to small leaks, not realizing that the leaks might be considerably larger while driving. After all, why worry about it if the car runs, right? Well, sooner or later the car won't run. My guess is that many of the catastrophic failures probably fall into that catagory.

I have Mobil-1 ATF in my car, and have never had a problem with it.

On a related note, since ATF is also used for the power steering in a 928, synthetic could also be used there. It will leak out of any questionable seals faster than conventional ATF there too though. I use conventional ATF in there hoping to prolong the time before I need a new steering rack.

dr bob

I think we are straying from the original question which concerned ATF and not engine oil.

The synthetic ATF is not thinner or thicker, does not have less friction or lubricate better than dino ATF. The benefit that I appreciate is that it doesn't burn until it gets a lot hotter. I use it in my Explorer tow vehicle for that reason. I put it in the 928 because it seemed like a good idea, but frankly I drive the car like a wimp almost all the time. It goes months without exceeding 3000 rpm, and seldom sees the bottom half of the pedal. Do I need synthetic ATF? No. I also don't need 17" rims, upgraded brakes, Michelin Pilots, hi-wattage headlights, etc. But I have 'em and seem to gather some measure of comfort knowing they are there just in case. In fact, that same thought can apply to the whole 928 ownership experience-- comfort in knowing it's there.

back to our regularly scheduled discussion...

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Thom1

Thanks Dr Bob for some more good information. Greg, Max, Jerry, Chris, and Mike - 2 thumbs up for your assistance too.

This is a very tough decision for me. I have another couple of days to decide, and talk with some victims that have lost their transmissions. But, I am thinking that I will stick with Mobil 1 ATF.
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Thom1

Hi again Sharks:

Guess what I found! A 2002 Higher Mileage ATF. 2001 Automotive Product Award Winner by “Lubricants World” It is Valvoline MaxLife, DexronIII, Mercron, Automatic Transmission Fluid. Formulated For Higher Mileage Transmissions! See valvoline.com/transmissions. The notes say that it addresses many issues such as reconditioning seals, reducing varnish formation, and smoother shifting. Plus, it is uder $4/quart. Note: Prices have been reduced on other ATFs.

What do ya’ think?
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Steve Cattaneo

Thom,
Switching from petroleum transmission fluid to synthetic fluid is perfectly safe. The technology used in synthetic oils make them completely compatible with petroleum oils. Synthetic oils are designed not refined.

The use of synthetic transmission fluid in a properly functioning transmission will not cause a catastrophic failure. If you have an existing oil leak the use of synthetic will make it worse. If you suddenly develop a leak, the seal was bad, it would have leaked any way. The lower viscosity of synthetic will blow by a bad seal. I know of 5 928 that have front seal leaks with petroleum fluid. Synthetic transmission fluid as well as petroleum-based fluids contains detergent, which will clean dirt deposits and accumulate into the filter, that’s why it is important to do a routine prevented maintenance to the transmission on a regular bases. Change your transmission fluid and filter every 30,000 miles or 2 years, which ever comes first, and don’t forget to drain the torque converter.

Stay with the synthetic, change the rear seal while the trans is out, you will have to unbolt the differantial from the transmission. The benefit of synthetic fluid out weights the cost.

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ViribusUnits

Something I rembered about synthetic vs. petrolium multiviscosity motor oils. I have no clue if it also applys to automatic tranys.

There are two ways to make a oil multiviscosity. One is to add "viscosity index modifyers" the other is to change the specific shape of the il's molicues to change with tempeture. Since "natral" oil is just sorted out, the only way to make it multiviscosity is to add the index modifyers.

The problem with "viscosity index modifyers" is that they have the consistancy of mud, when they're not disovled in oil. As a result, there is a certain amount of "stuff" disolved in the oil, and that loweres the solubility of certain other substances in the oil. If you accidently get into a situation where the oil is required to disolve alought of a waste, you could get into problems.

As a result, it seems preferable to uses eigher synthetic motor oil, or smaller diffrence multiviscosity motor oil. Instead of 10W-40, maybe 10W-20, etc...

Like I said, I haven't the fogyest clue if that has any relevence to ATF's situation. To be honest, I've never checked it with lab results, so any correlation would be nice.