Trans fluid for a 55 buick

[billbuickgs]

Type A is called for but can I add dextron  II or III to the existing fluid  ??

Bill

[old-tank]

Search and you will more of THIS.

[SpecialEducation]

FWIW:. GM does not license the Dextron III name, and Dex VI (note that we skipped 4&5) is lower viscosity than the previous fluids. Like engine oil, systems designed for higher vis fluid are likely to see accelerated wear with the lower vis fluid (you wouldn't put 5W30 in a Nailhead, would you?).

 

Because of this, there's still a huge market for Dex III, although nobody is allowed to use that name anymore. If you see funny verbiage on a bottle regarding the Dex III spec, it's not that they are trying to make you think it meets the spec when it doesn't. They can't call it Dex III anymore, but it's what you want. 

[NTX5467]

Dex VI is a synthetic-blend fluid.  Dex III (and similar) are normal dino formulations.  I know that when Dex IIE came out for the future electronic valve body THMs, as a short-lived pre-cursor of Dex III, it had a slightly quicker shift than the prior-spec Dexron II atf.  When Dexron replaced the prior Type A Suffix A atf, I don't recall any specific mention of internal changes in the TorqueFlites, THMs, or other automatic transmissions which had previously used Type A Suffix A atf . . . but I might have missed something, back then. 

 

GM stopped licensing Dex III (and prior versions) per se, just as Ford did with their Type F, so it's up to the oil companies to maintain the same level of product standards on their own.  You have to remember that any "spec" oil uses that spec as a minimum-specification to meet.  If a non-GM entity built a trans fluid to meet Dex III specs, once it met those specs there was nothing to really keep them from adding something to make it better, as long as the basic Dexron III spec was maintained.  This allowed other atf oil sellers to have synthetic Dexron III when the GM Dexron III atf was not synthetic, for example.  Or for "SL" rated motor oils to exist which are "dino", blended synthetic, and full-synthetic motor oils. 

 

GM has plainly stated that Dexron III atf was backward compatible all the way to 1947 model year GM vehicles.  Same with Dexron VI (asDex VI replaces the prior Dex III).  Viscosity might have a bearing on "protection", but a thick oil with no anti-wear additives typically results in less total life of the component than a lighter oil with a robust anti-wear additive package.  The slightly lighter viscosity oil will also allow the lube system to reach full pressure (especially on cold starts) quicker, thereby lessening the reliance on residual oil for initial start-up wear protection.  And, it'll take a bit less horsepower to turn the oil pump in the trans, which might also relate to engine starter life, too.  And you could probably say the same thing for 5W-30 motor oil in a 1950s era-design engine (provided all internal clearances are not excessive, as NailHead engines existed well into the multi-grade 1960s era, usually 10W-30).

 

End result is that we now have MANY choices of atf where there used to be few.  As many owners don't typically drive the vehicles which would used these atf products very much each year (probably about 5000 miles/year) even the older-spec Type A fluid should provide acceptable component life.  Considering how the component lives used to be when those same cars were "newer" or then-"used cars", when average yearly mileage was considered to be 12K/year.  In those prior times, it wasn't necessarily the base oil which "wore out" or was damaged by "heat", but the weaker additive package which depleted and required a fluid change as a maintenance item.  When the Dexron family came along, drain plugs in torque converters vanished, with fresh fluid every so often being enough to replenish the additive package for suitable longevity.  Each successive member of the Dexron family has addressed some operational or longevity issue, with the latest Dex VI fluid having the most robust package at that time (anti-wear, viscosity improvers, etc.).  Your money, your vehicle, YOUR choice.  There are some compelling reasons to seek out the old Type A atf, if you desire . . . but you have to look for it or find it online, typically.  It's got the particular additive package the trans was designed around . . . but the newer fluids have additive packages which are significantly better.  Just depends on what one might want to do!

 

NTX5467

 

 

[Paul Falabella]

I have been using Dex/Merc in my 55. It always leaked a bit. A few ounces added a year to top it off. I have noticed it is noticeably thinner and less red(pinkish) after a run on a hot day with A/C on. Been told this is normal. Especially since the 55 does not have a ATF separate cooler.

 Has anyone tried Valvoline High Milage ATF?  I use their high milage motor oil.

[billbuickgs]

THANK,

Found a sealed quart of dextron ATF in the garage .

 

Bill

[NTX5467]

The Valvoline "high mileage" atf has a bit of "seal expander" already in it.  Don't have to add any separately.  Might have a little better detergency additive package, possibly.  I think the "swell" factor is only about 1% or so?  Enough to soften aged rubber but not enough to really hurt anything.

 

GM used to have an "Automatic Transmission Conditioner" 1/2 pint (measure) additive which had the seal conditioner and detergent in it.  When I put some in my '77 Camaro at past 100K miles, it seemed to make it shift a little cleaner than before.  Back 40 years ago, adding that to the atf was part of a normal transmission service fluid and filter, at the dealership I work at.  No adverse affects in my car.  At that time, many hot rodders changed to Ford Type F for its quicker shift engagement characteritiscs in THMs and TorqueFlites.  Putting the GM additive in the atf seemed to get mostly the same effect.

 

NTX5467