opinion on synthetic transmission oil/fluids

Discussion in 'transmission and Drive train' started by grumpyvette, Nov 21, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    HEY! Grumpy, What's your opinion of synthetic motor oil and at what intervals do they recommend changing T56 6sp lube (normal driving) ? Thanks in advance

    motor oils
    heat and dirt and moisture in the engine oil are the problems, changing oil and filters tends to prevent problems, modern oils are far better than what we had in the past, but Id suggest no more than 5K miles between oil and filter changes with mineral base oils and changing the oil filter on synthetics at 5000-miles and changing the oil an filter at 10-15K. remember oil must reach about 215F to burn off moisture so don,t try to keep the oil temp lower than that all the time I generally try to keep engine oil temps in the 190f-215 range and don,t worry about oil temps reaching 250F for brief periods
    adding a few magnets to the oil pan helps trap metallic dust and crud btw.
    on synthetic oils, the advantage is slightly better film strength , better high heat lubrication,and a noticeably higher heat resistance to break down, most mineral base oils start to break down slowly at about 240F and bye 260F they start breaking down far faster, most synthetics easily operate up to 280F-290F without breaking down quickly
    keep in mind modern oils are designed to trap and transport crud to the filter, but it takes a decent filter to make the system work as designed, (removing the crud from the oil flow)
    almost all current oil is far better than what was available even 15 years ago!, and synthetic gear oil viscosity ratings DON,T MATCH engine oil ratings, GEAR OILS are a totally different deal from engine oils because they don,t need to be formulated to put up with combustion residues,MANY current SYNTHETIC GEAR OILS for most current MANUAL TRANSMISSIONS are FAR THINNER than the old MINERAL LUBES of the 1960s that were commonly used in the MUNCIE 4 SPEED transmission of the muscle car era., some resemble or even are ATF (AUTOMATIC TRANSMISSION FLUID) or similar oils, so they flow and lubricate far better when cold, and the newer formulas lubricate as well or better than the old style thicker lubes of the past





    http://www.machinerylubrication.com/art ... icleid=167

    https://www.mobiloil.com/USA-English/Mo ... -90LS.aspx

    quick story
    I had, at the time, a MUNCIE M21 in one of my corvettes,(the 1968)
    it worked ok but it always had a slight whine and shifts were a bit sluggish, ,after I had the car about a week, I mentioned that to a buddy who was a pro nascar mechanic at the time, he ask me about the lube,I was using,Id just filled the trans with the chevy dealer recommended lube so I told him it was full and new,( I had no clue (back in 1971) synthetics were almost unheard of back then, ) he brought some over to the house amd we drained the old lube, replaced it with what he swore was what they used at his shop.......the difference was ASTOUNDING, the whine disappeared, the shifts smoothed out over the first few hours, I could hardly believe it was the same transmission. yes theres advantages, and yes Id recommend a good synthetic like MOBILE or AMSOIL
    manual transmissions generally benefit from oil changes about every 60K

    most problems are the result of not changing the filters frequently enough, once the filter medium becomes partly clogged the filter rapidly starts to bye-pass at least some percentage of the oil during cold starts and rapid changes in rpm levels, most of the cleanable filters Ive examined have very limited surface areas so they would need to be cleaned very frequently.
    the better throw always have 400 sq inches of surface area, Ive never seen a single cleanable oil filter that states their screens surface area but looking at them Id be amazed if it exceeded 220 sq inches
    look closely at the design of the filters and you'll see the differences

  2. DrJ

    DrJ New Member

    C5 6 sp manual, 2000
    dextron 3 recommended by GM, but how about newer dex 6?

    currently only Dex 3 type oil in parts stores is called "DEX/Merc," claimed to be compatible with Dex 3 and for GM trans up to 2005 . this ATF appears to be "non-synthetic"

    debate exists about using newer Dextron 6 in the 6 sp manual, which also claims to be compatable with Dex 3, this ATF is definitely a synthetic type.

    opinions suggests the 2000 6 speed cannot use the newer dex 6, despite label claim to be backwards serviceable with Dex 3. it has been explained that the backwards serviceability is limited to auto trans not the manual.

    I would prefer to use dex 6 as a synthetic but perhaps need to stay with non-synthetic dex 3?
    if so is the "dexMerc" the correct one to use?
  3. grumpyvette

    grumpyvette Administrator Staff Member

    For anyone else reading this,
    I would avoid useing any auto trans fluid in any manual transmission,unless the shop manual for your year car suggested its use,yes Im fully aware that the owners manual specifically lists its (DEXTRON III) use, yes IM fully aware its done quite comonly, dextron III is the suggested lube in your 2000 corvettes manual transmission,but theres differant requirements and a specific lubericant, thats designed for use in a manual trans ,and it is almost always prefered. that being said, I think youll be fine with either dex 3 or dex 6, but because dextron 3 is the listed lubericant Id be tempted to stick with that to prevent, having some dealership or transmission shop tell you you were useing the wrong fluid.
    synthetics designed for manual transmission use tend to have higher heat tollerance and longer useful life expectancy, and there is probably some advantages, but I don,t see any info suggesting that the dextron III is not doing a decent job, either.

    keep in mind auto transmissions need to have clutchs grab and hold and while a manual trans is more concerned with high pressure gear lubrication, and long term heat breaking down the fluid, as most manual transmissions don,t run trans fluid coolers.
    you might want to call GM POWER TRAIN for thier input,
    but following the OEM manufacturers suggested spec sheet info is probably the best idea. as they have tested a great deal and should know what works, best.

    http://www.chevron.com/products/ourfuel ... xtron.aspx

    -800-LUBE-TEK (800-582-3835)

    http://www.amsoil.com/products/transmis ... zo=1345085

    Product Technical Services: (715)399-TECH


    Tel: (314)865-4100

    http://www.expertvillage.com/video/1261 ... ission.htm

    http://www.mobil.com/USA-English/Lubes/ ... uid_50.asp

    1-800-ASK MOBIL (275-6624)
    Last edited by a moderator: Nov 12, 2017
  4. wagonmaster

    wagonmaster Member

    Those that come with ATF (Mustang AOD and Corvette, Etc will benefit greatly with synthetic fluids! Wear better, and more "free" HP!!
  5. DrJ

    DrJ New Member

    Thank you for reply with extra links. Sorry to beat this dead horse again.

    there has been some post s advising the C5, 6 sp manual trans oil has been changed by GM from DEX III, to GM part number: :88861800 "Transmission and transfer case oil" specifically not the synchromesh.

    have u heard this too? would it be a big upgrade from the DEX III?

    I went to all those links, thank you

  6. grumpyvette

    grumpyvette Administrator Staff Member

    that was a good knowledgable question, keep posting :mrgreen:

    BTW info you might want


    http://autos.yahoo.com/maintain/repairq ... 123_0.html


    How often should the automatic transmission fluid be changed?
    Most owner's manuals say it isn't necessary. Yeah, right. That's why transmission shops are making a fortune replacing burned out automatic transmissions.

    For optimum protection, change the fluid and filter every 30,000 miles (unless you have a new vehicle that is filled with Dexron III ATF which is supposed to be good for 100,000 miles).

    Why Atf Wears Out
    An automatic transmission creates a lot of internal heat through friction: the friction of the fluid churning inside the torque converter, friction created when the clutch plates engage, and the normal friction created by gears and bearings carrying their loads.

    It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in motion. Normal driving will raise fluid temperatures to 175 degrees F., which is the usual temperature range at which most fluids are designed to operate. If fluid temperatures can be held to 175 degrees F., ATF will last almost indefinitely -- say up to 100,000 miles. But if the fluid temperature goes much higher, the life of the fluid begins to plummet. The problem is even normal driving can push fluid temperatures well beyond safe limits. And once that happens, the trouble begins.

    At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt toast. As heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins to form on internal parts (such as the valve body) which interferes with the operation of the transmission. If the temperature gets above 250 degrees F., rubber seals begin to harden, which leads to leaks and pressure losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even more. Eventually the clutches burn out and the transmission calls it quits. The only way to repair the damage now is with an overhaul -- a job which can easily run upwards of $1500 on a late model front-wheel drive car or minivan.

    As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half!

    At 195 degrees F., for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240 degrees F., the fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to 5,000 miles. Go to 295 or 300 degrees F., and 1,000 to 1,500 miles is about all you'll get before the transmission burns up.

    If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again. According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission failures are caused by overheating. And most of these can be blamed on worn out fluid that should have been replaced.

    On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the bottom or end tank of the radiator. Hot ATF from the transmission circulates through a short loop of pipe and is thus "cooled." Cooling is a relative term here, however, because the radiator itself may be running at anywhere from 180 to 220 degrees F.!

    Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that enters the radiator cooler at 300 degrees F. leaves at 240 to 270 degrees F., which is only a 10 to 20% drop in temperature, and is nowhere good enough for extended fluid life.

    Any number of things can push ATF temperatures beyond the system's ability to maintain safe limits: towing a trailer, mountain driving, driving at sustained high speeds during hot weather, stop-and-go driving in city traffic, "rocking" an automatic transmission from drive to reverse to free a tire from mud or snow, etc. Problems in the cooling system itself such as a low coolant level, a defective cooling fan, fan clutch, thermostat or water pump, an obstructed radiator, etc., will also diminish ATF cooling efficiency. In some cases, transmission overheating can even lead to engine coolant overheating! That's why there's a good demand for auxiliary add-on transmission coolers.

    Auxiliary Cooling
    An auxiliary transmission fluid cooler is easy to install and can substantially lower fluid operating temperatures. The plate/fin type cooler is somewhat more efficient than the tube and fin design, but either can lower fluid temperatures anywhere from 80 to 140 degrees when installed in series with the stock unit. Typical cooling efficiencies run in the 35 to 50% range.

    Atf Fluid Types
    What kind of automatic transmission fluid should you use in your transmission? The type specified in your owner's manual or printed on the transmission dipstick.

    For older Ford automatics and certain imports, Type "F" is usually required. Most Fords since the 1980s require "Mercon" fluid, which is Ford's equivalent of Dexron II.

    For General Motors, Chrysler and other imports, Dexron II is usually specified.

    NOTE: Some newer vehicles with electronically-controlled transmissions require Dexron IIe or Dexron III fluid. GM says its new long-life Dexron III fluid can be substituted for Dexron II in older vehicle applications.

    CAUTION: Using the wrong type of fluid can affect the way the transmission shifts and feels. Using Type F fluid in an application that calls for Dexron II may make the transmission shift too harshly. Using Dexron II in a transmission that requires Type F may allow the transmission to slip under heavy load, which can accelerate clutch wear.

    Changing The Fluid
    It's a messy job because there's no drain plug to change the fluid, but you can do it yourself if you're so inclined. To change the fluid, you have to get under your vehicle and remove the pan from the bottom of the transmission.

    When you loosen the pan, fluid will start to dribble out in all directions so you need a fairly large catch pan. You should also know that removing the pan doesn't drain all of the old fluid out of the transmission. Approximately a third of the old fluid will still be in the torque converter. There's no drain plug on the converter so you're really only doing a partial fluid change. Even so, a partial fluid change is better than no fluid change at all.

    A typical fluid change will require anywhere from 3 to 6 quarts of ATF depending on the application, a new filter and a pan gasket (or RTV sealer) for the transmission pan. The pan must be thoroughly cleaned prior to reinstallation. This includes wiping all fluid residue from the inside of the pan and scraping all traces of the old gasket from the pan's sealing surface. Don't forget to clean the mounting flange on the transmission, too.

    When the new filter is installed, be sure it is mounted in the exact same position as the original and that any O-rings or other gaskets have been properly positioned prior to tightening the bolts. Then tighten the bolts to the manufacturer's recommended specs.

    When refilling the transmission with fresh fluid, be careful not to allow any dirt or debris to enter the dipstick tube. Using a long-neck funnel with a built-in screen is recommended.

    CAUTION: Do not overfill the transmission. Too much fluid can cause the fluid to foam, which in turn can lead to erratic shifting, oil starvation and transmission damage. Too much fluid may also force ATF to leak past the transmission seals.

    Add half a quart at a time until the dipstick shows full. The transmission really isn't full yet because the dipstick should be checked when the fluid is hot, and the engine is idling with the gear selector in Park. So start the engine, drive the vehicle around the block, then recheck the fluid level while the engine is idling and add fluid as needed until the dipstick reads full.

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