Fluid change advice.

[PauliusB]

Hi!

 

I have 1980 Buick Riviera 3.8L V6 Turbo. I was able to finally start it after it's been sitting for over 10 years and would like to do a proper fluid change of transmission and differential, but have a few doubts since I don't have owner's manual.

 

1. What type of transmission fluid type I should use? Does this one from Valvoline good enough? What's the typical fill volume in quarts?
 

2. Again what type of differential fluid I should use, could you provide some examples? I know that fluid type should be based on diff type, does anyone know what options for differential were available for this car? Open diff is the most common, but just want to make sure. What's the typical fill volume in quarts?

 

Anything else I should know maybe? Any advice is welcome.

 

Thank you very much!
Paulius

Edited November 5, 2023 by PauliusB (see edit history)

[RivNut]

All that I know is that the transaxle in a turbo car has a 3.23 final drive rather than the standard 2.73

Edited November 5, 2023 by RivNut (see edit history)

[NTX5467]

Back then, an earlier member of the Dexron family of fluids, which were non-synthetic (i.e., "Dino") atf was all we had OEM.  Which means the last version of it would be Dexron III.  The later Dexron VI, as pictured, is backward compatible all the way back to the first DynaFlow or Hydra-Matic automatic, according to GM.  It is now a full-synthetic fluid.  GM does not license any atf prior to the current Dex VI.  ACDelco chemicals now terms the prior Dexron III as "Type III", I believe?  Other brands now term it "Multi-Make" and mention on the back of the bottle that the main application was GM Dexron III automatic transmission fluids, so have to read to find that.  Those Multi-Make and ACD Type III fluids will be less expensive than the Dexron VI fluids, by observation.

 

Personally, I think I'd seek out some of the earlier-spec fluids to be compatible with Dexron III fluids, just for general principles.  Then, after things are operating well, change to the Dexron VI atf if desired.

 

I don't recall anything special in the way of drive-axle fluids back then.  If you pull the plug and smell of it, if it smells like hypoid gear grease, that's what it is.  Commonly-available stuff, 80W-90 should work fine, if that's what it is.  In some of the oil company websites (i.e., Valvoline, Castrol, etc.) there should be a utility to find their lubes for various cars.  Just input the vehicle data and it spits out the results.  Only thing is they might not go back that far for you.  In which case a Google search might be operative, unless somebody comes up with an Owner's manual or Buick Service Manual information.

 

To ease the extraction of those fluids, you can buy an electric extraction pump at Home Depot or Amazon.  It is a small electric pump with long sections of small diameter clear tubing for the intake and outlet sides of the pump.  Powered by a car battery or similar.  At Home Depot, look for an extraction pump to do oil changes on riding lawn mowers, but works for cars, too.  Used to be about $30.00 USD several years ago.

 

In the transmission fluid capacities, there are TWO capacities.  One if a complete refill if the transmission is being assembled after a rebuild and the other, lesser amoiunt, one is for a simple filter change and refill.  You'll need the second one.

 

Hope this might help,

NTX5467

[RivNut]

The transmission is either a TH325 or a TH325-4L. The TH325 is a three speed whereas the TH325-4L is a four speed overdrive.  You might be able to find some info online that would give you the information you’re looking for. 

[BrianM]

I have had good luck with this version of Valvoline:

But I have no knowledge of your specific year, I have ran it in older and newer versions of GM transmissions with great results. 

[EmTee]

On 11/5/2023 at 12:05 PM, NTX5467 said:

Personally, I think I'd seek out some of the earlier-spec fluids to be compatible with Dexron III fluids, just for general principles.

I agree with NTX.  I would use the Valvoline Dexron III/Mercon ATF rather than the Dexron VI.  I changed the Dexron III in the transfer case of my '04 Silverado to Dexron VI thinking the synthetic version would be better.  Shortly after the change the transfer case started refusing to shift in or out of 4WD unless at a dead stop.  Looking online, I discovered this was a common complaint.  Dexron VI is 'slipperier' than Dex III and the synchros don't like it.  With that, I can't help but think what might happen when 40 year-old clutches are bathed in Dexron VI.  I'm planning to change the trans fluid in my wife's '93 Allante and my '01 Suburban and will be using the Valvoline Dexron III/Mercon ATF in both vehicles.  I currently have it in my '67 Riviera and it performs just as the original Dexron fluid did.

 

Edited November 8, 2023 by EmTee (see edit history)

[Seafoam65]

Having been in the car repair business for 47 years, I can tell you absolutely that changing the trans fluid

comes with significant risk. I learned this on my GTO back in 1972. My 40,000 mile three year old turbo 400 only lasted two weeks after servicing the trans. That same trans now has the same 51 year old fluid in it from

the 1972 rebuild and shifts perfectly at 165,000 miles. My customers all knew not to request a transmission fluid change because I would not do it under any circumstances. One of my employees who worked the front desk at my shop knew to explain to people why I don't service transmissions. He owned a 34 foot GMC motorhome and went on vacation in Colorado. While in Colorado one of his plug wires started misfiring at 40,000 miles and he took it to a motorhome repair GM dealership in Denver. The service writer talked him into

changing the trans fluid and filter while it was in the shop. All the while he was thinking to himself that Winston

would kick my ass if he knew what I was doing. After they were done with the work, he drove out of the dealership, proceeded to drive 150 miles and the transmission went completely out with neutral in all forward gears and reverse. He had it towed to the next town and paid 4,000 dollars to get it fixed. He called back to the dealer who serviced the trans in Denver and they told him that they would not accept any blame, after all, all they did was change the fluid.........SORRY!

[Seafoam65]

 Oh by the way.......my 99 Ford Expedition that has towed an 8,000 pound car hauler it's whole life

has it's 1999 trans fluid and filter in it at 350,000 miles and it shifts perfectly. I towed my trailer this

summer from Texas to Kalamazoo Michigan and back with this trans and no problems. If you don't

learn anything else from this forum if you take my advice regarding this matter you will be way way ahead

regarding car repair expenses.

[Bloo]

I don't know if I would be willing to accept "too slippery" as the reason for any trouble. DexronII/III/Mercon's claim to fame was the presence of friction modifiers. Type F was the one without all the slipperiness. Some newer ATFs are lower viscosity in the interest of fuel savings. I can see that potentially being an issue in a transmission designed around more viscous fluid.

 

For what it's worth, when you drop the pan and change the fluid and filter in a car as new as 1980, there will probably be no torque converter drain. Only a small portion of the fluid will actually get changed. Most of the old fluid will stay in. If I were doing this, I would get the DexronII/III equivalent. In Valvoline, you'll have to look in the small print on the back to see which one that is.

 

 

[EmTee]

6 hours ago, Bloo said:

I don't know if I would be willing to accept "too slippery" as the reason for any trouble.

Too 'slippery' was the issue for my transfer case synchros.  That said, I still have it in the truck as the ability to 'shift-on-the-fly' is not high on my must-have list.

 

6 hours ago, Bloo said:

Some newer ATFs are lower viscosity in the interest of fuel savings. I can see that potentially being an issue in a transmission designed around more viscous fluid.

This is really my main concern WRT use of Dexron VI in an older transmission.  I noticed the lower viscosity of the Dexron VI when I poured it in.  My concern, and maybe related to Seafoam's observations, is lower viscosity may lead to lower line pressures in transmissions with high miles or old seals due to wear and/or seal shrinkage.  That's why I prefer to stick with a brand-name Dexron III replacement for older GM vehicles.

 

6 hours ago, Bloo said:

For what it's worth, when you drop the pan and change the fluid and filter in a car as new as 1980, there will probably be no torque converter drain. Only a small portion of the fluid will actually get changed. Most of the old fluid will stay in.

That's why I try to change the fluid every ~50K miles.  That ensures the old fluid isn't excessively dirty or burnt.  I prefer changing 40 ~ 50% of the fluid every 50K miles rather than flushing 100% of the fluid at 100K miles...

[NTX5467]

The Dex III-type Valvoline atf is available in gallon jugs, if desired.  GM used to have some specific transfer case fluids.

 

GM plainly states the Dex VI is backward compatible all the way to the first Hydra-Matics in the late 1940s.  BUT they also have some different fluids for more recent automatic transmissions.  BTAIM

 

Enjoy!

NTX5467