Synthetic Oils in Auto Trans & Differentials

[Hutch C.]

Does anyone have experience with converting C-3 auto trans and read endds to synthetic oils? I have made the switch in the engine and am now cosidering trans & differential.

 

[GTR1999]

Some debate on that. I don;t use them when rebuilding either. For trannies,if you get ALL the old fluid out you could switch to Ford or B&M fluid for more performance-how much ???? You would have to remove the convertor to drain it or maybe drill a hole in it-I wouldn't.

For rear ends I stay with the GM posi additive and 90 wt gear oil.

 

[Vettehead Mikey]

There's no proven benefit, so why bother?

 

[lnirenberg]

... I have made the switch in the engine and am now cosidering trans & differential.

I was considering a switch to synthetic engine oil but in asking around I found out that synthetic engine oil is thinner that petroleum based oils and in older cars it may leak in places that never leaked with regular old oil.

 

[Billybeau1]

I was considering a switch to synthetic engine oil but in asking around I found out that synthetic engine oil is thinner that petroleum based oils and in older cars it may leak in places that never leaked with regular old oil.

That may be true, however I've been told by many long time mechanics that they have never seen a regular oil that can hold a candle to synthetic. I put 10w40 full synthetic in my 74 and dont see any leaks. I feel good about the extra protection.

 

[ßill]

What a bunch of pessimist around here. From what I read, the molecules in synthetic oils are smaller and if an imperfection exists in a seal the oil may leak out That’s the only down side I see. The lubricating properties are much better with synthetics as is the heat handling capacity. I use synthetic oil in every thing drive, from a 1950 Chevy P/U to a 2000 Escalade, including a ’78 Mercuiser powered boat. Here is a picture under the rocker cover of my daughter’s ’90 Honda with 190,000 miles on synthetic oil.

 

[Hib Halverson]

Clearly, there's a lot of misconceptions about the use of synthetic lubricants in rear axles and automatics.

First the statement...

There's no proven benefit, so why bother?

...is not correct.

Fact: there is a benefit in synthetic lubricants, especially with rear axles. That's why the C5/C6, some GM trucks and other vehicles use synthetic gear lubes. The main benefit is improved durability at higher lubricant temperatures. Both the high-performance and the towing/hauling duty cycles put a lot of temperature into rear axle lubes and that's why the OEs are using them. Further...depending on the specific type of synthetic lubricant, there even can be a temperature reduction when using them because of some synthetic's better lubrication.

The statement that synthetic lubricants have "smaller molecules" is urban legend. There is a seal compatibility issue between some rubber lip-type seals used prior to 1980 and some synthetic lubricants. If you've got a component with seals dating to before 1980, you switch to a synthetic lubricant and the type of material used in the component's seals is not compatible with that synthetic, then you might have a leak, but it's not that the lube "permiates" though the seal, rather, the lube "attacks" the seal material. The seal industry, generally, has used "synthetic friendly" materials since the early 80s. I have synthetic lubricants in the rear axles of all my cars, some of which date to 1965, however, the axles in those older vehicles have been overhauled at least once since 1980 so they have modern seals.

As for synthetic lubricants in automatic transmissions, that is nothing but a win-win. Synthetic automatic transmission fluids survive better under high temperatures. Excessive fluid temp is a major problem with automatics in high-performance or towing/hauling duty cycles. It doesn't take a rocket scientist to understand that if the temperature tolerance of the fluid is higher, then durability during extreme duty will be better. I use synthetic ATF in any transmission that calls for automatic transmission fluid as a lubricant.

Mobil 1 markets both gear lubricant and ATF and it's a good product. Red Line Synthetic Lubricants also offers gear lubes and ATF, but has a more broad product line than M1. I feel RL's ester-based synthetics are a slight measure better than Mobil's and, because of that, I use Red Line gear lubricants and ATF.

 

[Vettehead Mikey]

Hib,

As always, my statements apply strictly to the vehicle in question, not some other car or truck or engine type. Yes, there are applications where these oils are mandatory or beneficial- that's (generally) what they were developed for in the first place.

Making a leap of logic by assuming that if it's used in a modern GM truck then it must be 'better' for my 35 year old Corvette is just bad science in my book.

Please show me proof that any C1/C2/C3 transmission, engine or rear ended lasted longer solely because of synthetic oils, then I'll be convinced.

 

[mrvette]

All I can say is changing the tranny fluid in my olde Muncie 4 speed, right there in the car...'72, changed that tired ole hard shifting tranny into a slick as anything modern, that thing snuck throug the gears like a bicycle....I used 20w50 Mobil I engine oil....

I would imagine using syn engine oil, say 30 weight, with GM additive would help may a differential too, run MUCH cooler....IN all honesty I can't remember if I did that to the vette or not, which vechicle I did that too....

GENE

 

[Vettefan87]

Hib,

As always, my statements apply strictly to the vehicle in question, not some other car or truck or engine type. Yes, there are applications where these oils are mandatory or beneficial- that's (generally) what they were developed for in the first place.

Making a leap of logic by assuming that if it's used in a modern GM truck then it must be 'better' for my 35 year old Corvette is just bad science in my book.

Please show me proof that any C1/C2/C3 transmission, engine or rear ended lasted longer solely because of synthetic oils, then I'll be convinced.

You do not have to run synthetic, it is your choice. Do you want your engine and drive line componets to last longer? If you answer yes, then you want to use synthetic. There is a reason why Mobil 1 Synthetic is factory fill for the Newer cars. It is better oil.

Thanks Hib for clearing up the oil particles in synthetic oils are not smaller. I always believed that they were.

 

[GerryLP]

Anecdotal "evidence"

I purchased a 1989 Jeep Cherokee in that year, and I switched to Mobil1 once the break-in requirements were met (1,000 miles at 55 MPH or below). I wish I could have taken pictures of the internal engine components at the time;however, I set out to correct all oil leaks at around 190,000 miles, and the short block looked great then. Gave it to my kid 3 years ago, and he still had it until 6 months ago when he sold it at 238,000 miles (he has been to Iraq on two tours already). Now he wishes he would have kept it. The SUV still running around strong and working just fine for his buddy whom he had sold it. They're both stationed at Camp Pendleton, CA.

The L81 short block components and heads are in "perfect" condition. I switched to Mobil1 at around 33,000 miles, and at 152,000 miles, the components look great. No bearing scratches or gauges or anything. I do have a small scratch on the #8 cylinder, but since the piston rings are in great shape, I can't prove either way that the damage was helped by the oil, or if it was just something that made it through the induction.

Our 98 Diamante is using Mobil1 now. A recent compression and bottom end inspection and testing revealed "factory" levels of PSI readings in the compression (153 - 155 PSI) in the cylinders. The bottom end looked very clean, and still runs like a champ at 95,000 miles. We switched to Mobil1 at around 26,000 miles.

My experience may seem anecdotal to everyone else, but I find comfort on the "historic" reliability on previous and current vehicles. And by the way, we did not changed the oil often either. We averaged between 6,000 and 7,000 miles in between oil changes. In some vehicles, that was no more than 3 oil changes in a year.

GerryLP:cool

 

[Vettehead Mikey]

Jerry,

Nothing personal, but your story is typical of the evidence that people put forward in an effort to show that synthetics make engines last longer. Problem is that there's just as many stories around of people using regular oil where the engines lasted just as long or longer (including me).

This is not some new crusade for me- I've been closely involved with synthetic oils since 1978 when I started my OEM aviation career and as I've said before, I'm still looking for proof.

 

[GerryLP]

Jerry,

Nothing personal, but your story is typical of the evidence that people put forward in an effort to show that synthetics make engines last longer. Problem is that there's just as many stories around of people using regular oil where the engines lasted just as long or longer (including me).

This is not some new crusade for me- I've been closely involved with synthetic oils since 1978 when I started my OEM aviation career and as I've said before, I'm still looking for proof.

Not at all! I don't take the free exchange of views in a personal way.

You're correct. My experiences are no proof whatsoever; that's why they are anecdotal.

One can achieve the same results by changing the oil every 3,000 miles. The drawback on not doing so with the mineral oil is that mineral oil tends to breakdown sooner and at lower temperatures than synthetic, and thus, it produces by-products that turn into what we call oil sludge and what not.(but again, this is what I have read in articles over the years). This oil sludge is what traps metal particles normally produced through wear. This trapped metal makes its way into tight clearance areas and become a problem.

Hasn't anyone conducted a test with measurable results on this issue? I suspect, generally speaking, that one would need two blue printed engines with the same specifications (one filled with mineral oil and the other synthetic oil), a dyno, and a test sequence that would pace both engines through the same loads. Finally one would probably need a laboratory test that would gage the characteristics of the oil after the test, and arrive at some sort of conclusions (if possible).

If a vehicle has an easier "life" than other vehicles, then this would also play a factor on how well the mineral oil stands up to the vehicle duty cycle. Definetely, preventative maintenance is directly related to vehicle reliability and long lasting operation, but as the law of diminishing returns would advice us, the more effort ($$$) we put into the preventative maintenance of a vehicle, we will reach a point that will produce ever decreasing returns on the investment.

I choose to use Mobil1, for it allows me to not sweat or worry about the oil change every 3,000 miles. (again, this 3K miles reference point is dependent on hard one beats the vehicle).

GerryLP:cool

 

[Santovenia]

How often is it necessary to replace the oil in your car if you're using synthetic?
I've heard a range of answers from as far as every 3000 miles to every 30000, what is the correct response? I understand there are differences among manufacturers so please specify for which brand and specific oil you're referring to.

 

[Vettefan87]

Hopefully Hib will respond to this, he really knows what he is talking about. It all really depends how you drive your car, and how hot the oil temps are. Once I start running synthetic I will probably change it around ever 5 thousand miles or so.