TH350 Fluid Type and Capacity: DEXRON Spec, Refill, Dry Fill and Converter Quarts

Ask five people at a car show what a TH350 holds and you will hear five numbers, anywhere from 3 quarts to 12. They are not all wrong. They are answering different questions: how much goes back in after a pan drop, how much the case and pan hold, and how much the whole system takes when the unit, converter and cooler are bone dry. Mix those up and you either overfill a perfectly good transmission or start a fresh rebuild a few quarts low.

This guide sorts out the fluid type and every capacity number that matters on a Turbo Hydra-Matic 350 (including the 1980-up TH350C lockup version), using GM's own service literature, the converter and pan makers' published capacity charts, and the fluid makers' spec pages. The full source list is at the bottom.

Recommended TH350 parts

The right fill for a Turbo 350: GM-licensed DEXRON VI or a DEXRON III-type ATF by the gallon (a dry rebuild takes two to three gallons), plus a TH350 transmission cooler to keep that fluid out of the burn zone. Ships from the USA. Secure checkout.

ACDelco GM Original Equipment 10-9395 Dexron VI Automatic Transmission Fluid, 1 Gallon

$59.99View part

Castrol Transmax DEX/MERC ATF 1 Gallon - Dexron III / Mercon

$52.99View part

TH350 Transmission Cooler

$65.31View part

The Quick Answer

The last line is the one people get wrong, so the rest of this article explains where each number comes from and how to finish every fill the same way: by the dipstick, engine running, at the temperature GM specifies.

Fluid Type: What GM Called For and What to Buy Now

GM's 1976 light truck service supplement (ST-330-76) is plain about it: use automatic transmission fluid "identified with the mark DEXRON II" in the Turbo Hydra-Matic 350 and 400. The earliest TH350s, which arrived for 1969, were filled with the original DEXRON that GM introduced in 1967; DEXRON II replaced it in the early 1970s and is what most service literature for this unit lists.

You cannot buy DEXRON II by that name anymore, and you do not need to. The fluid has been superseded several times, and the current GM specification, DEXRON VI, covers the old units too. Valvoline's product page for its GM-licensed DEXRON-VI/MERCON LV fluid states that it is "fully back-serviceable, so it can be used wherever Dexron-II and/or Dexron-III are recommended." William C. Anderson put it more bluntly in Old Cars Weekly, writing that DEXRON VI can be used in every GM automatic back to the beginning. The ACDelco 10-9395 DEXRON VI that GM sells over its own parts counter is marketed as the replacement for DEXRON III and DEXRON II(E) as well.

Is DEXRON VI too thin for an old TH350?

This is the question I hear most from guys rebuilding a Turbo 350 for a hot rod. DEXRON VI is a lower-viscosity fluid. Lubegard's ATF history notes that GM moved to DEXRON VI in 2005 at about 6.4 cSt at 100 C, while the older GM and Ford specs required 6.8 cSt or higher, with most fluids running 7.0 to 7.5 cSt. That difference is real. What offsets it is that DEXRON VI is far more shear-stable than the old Group I fluids; it holds its viscosity for the life of the fill, where DEXRON II-era fluid sheared down with hot miles. That is why GM licenses it as the back-service fluid. On a street TH350 with a sound pump and bushings, licensed DEXRON VI is the correct fill. A DEXRON III-type fluid such as Castrol Transmax DEX/MERC is also fine if that is what you prefer or already have on the shelf. Pick one and do not mix brands on a fresh build.

What not to put in a TH350

• Type F. Some racers used to run Type F in GM units for a firmer shift. Old Cars Weekly points out that Type F is the requirement for 1961 to 1981 Ford transmissions, not GM. If you want firmer shifts, change the valve body calibration or add a shift kit, not the fluid.
• "Multi-vehicle" fluids that do not state DEXRON compatibility. Read the label. If it does not list DEXRON II or III or carry a DEXRON VI license, it is not a TH350 fluid.
• ATF+4 or import-specific fluids. They are written around other manufacturers' friction materials and are not GM specs.
• Stop-slip additives as a fix. If a TH350 is slipping on correct fluid at the correct level, it has a mechanical or hydraulic problem. Our TH350 common problems guide covers what to check, and line pressure testing is the fastest way to prove it.

Capacity, Part by Part

1. The pan: what a service actually replaces

Per GM ST-330-76, after you drain the sump of a TH350 you add approximately 2-1/2 U.S. quarts (2 Imperial quarts) of fresh fluid to bring the level back to the proper mark. The TH400 takes about 7.5 pints by the same procedure. That is the number for a routine stock-pan service, and it is a lot less than most people expect. If the dipstick reads right after 2-1/2 quarts, stop. Do not keep pouring because it "should" take more.

2. The transmission itself with a stock pan

TCI's published fluid capacity chart lists the TH350 with a stock pan at 4 quarts, compared with 6 for a TH400 and 6 for a 700R4/4L60E. That figure is the transmission side only, without the converter. The difference between TCI's 4 quarts and GM's 2-1/2 is fluid that stays behind in the drums, valve body passages and case when you drain the pan. It does not come out on a pan drop, and it is already in there when you refill.

3. The converter

TCI's converter chart is the cleanest reference I know of: a new, empty converter holds about 5 quarts at 13 inches, 4 at 12 inches, 3.5 at 11 inches, 3 at 10 inches, 2.5 at 9 inches and 2 at 8 or 7 inches. A stock TH350 converter is in the 12-inch class, so figure about 4 quarts. Most aftermarket street and strip converters run 10 to 11 inches and hold 3 to 3.5. TCI adds two notes that matter on the bench: those numbers are for a new converter, since a previously run converter retains some fluid, and you should always fill a new converter before installing it.

4. The cooler and lines

Nobody publishes one number here, because it depends on the radiator tank cooler, the line length and any auxiliary cooler you added. A plate-type auxiliary cooler with several feet of line can easily add a quart or more. This is why a fresh rebuild that "should" take 8 quarts sometimes takes 9 or 10, and why you never fill by the bottle count.

5. Deep pans

A deep pan changes the math on every service. B&M's instructions for its 30280 cast aluminum and 30289 chrome steel TH350 deep pans call for adding about 6 quarts after installing the pan, then finishing by the dipstick. They use a filter extension so the pickup stays submerged in the deeper sump, and the drain plug turns every future service into a drain and fill. If you run a deep pan, write the actual refill quantity on a piece of tape under the hood after the first service so you are not guessing next time.

Filling a Rebuilt or Dry TH350

This is where the capacity numbers earn their keep. A dry TH350 with a dry 12-inch-class converter and a stock pan needs about 4 quarts for the unit plus about 4 for the converter, roughly 8 quarts before the cooler circuit. Here is how I fill one:

1. Pre-fill the converter. Before it goes on the input shaft, pour in 1 to 2 quarts, keeping it tilted so it does not spill during install. This follows TCI's advice to fill a new converter first and gets oil to the pump on the first crank.
2. Seat the converter fully. Make sure it is engaged on the pump drive before you bolt the transmission up. A converter that is not fully seated will break the pump when the bellhousing bolts pull it in.
3. Add about 4 quarts through the dipstick tube with the engine off.
4. Start the engine and keep adding at idle, in Park, until the level shows on the stick. Do not rev it.
5. Cycle the shifter slowly through every range with your foot on the brake, pausing a few seconds in each, to fill the clutch drums and servo circuits. Return to Park and recheck.
6. Bring it up to temperature and set the final level using GM's hot-check procedure below.

Have three gallons on hand for this. You will probably use a little over two, but running dry halfway through a first fill is how new converters and pumps get starved.

Checking the Level the GM Way

More TH350s come back overfilled than underfilled, and GM explains why in ST-330-76: the fluid level rises more than 3/4 inch as fluid temperature goes from 60 F to 180 F, so a cold stick reads low and people keep adding. Overfilling causes foaming and fluid loss through the vent, and GM warns that slippage and transmission failure can result. Too low causes slipping too, especially cold or on a hill.

GM's procedure:

• Engine running, shift lever in Park, vehicle level.
• If the vehicle has been towing, run at high speed, or sat in hot city traffic, wait about 30 minutes for the fluid to cool before you trust the reading.
• Fluid cool (about room temperature, 65 to 85 F): level should be 1/8 to 3/8 inch below the ADD mark. The dipstick has two dimples below ADD to show that range.
• Fluid warm: level close to the ADD mark.
• Fluid hot (too hot to hold comfortably): level between ADD and FULL.
• It takes only one pint to raise the level from ADD to FULL on a hot transmission, so add in small amounts.

B&M's deep pan instructions note that automatic transmissions operate between about 150 F and 250 F. If your hot readings are coming from a unit living at the top of that range, the fluid is working too hard; see our TH350 overheating prevention guide for cooler sizing.

How Often to Change It

GM's book interval for the TH350 is fluid and filter every 60,000 miles in normal service, or every 15,000 miles in severe service: heavy city traffic where outside temperatures regularly reach 90 F, very hilly or mountainous driving, frequent trailer pulling, or commercial use such as taxi, police or delivery work. Most TH350s still running today are tow rigs, hot rods and trucks that sit and then work hard, so treat them as severe service. If you are about to change fluid on a high-mileage unit with an unknown history, GEARS magazine's advice applies: drive it first so you know how it behaved, look at what is in the pan, and lean toward partial changes over a single complete exchange. Our TH350 fluid change cost breakdown walks through the pan-drop math.

FAQ

What type of transmission fluid does a TH350 take?

GM specified DEXRON II for the Turbo Hydra-Matic 350. Current GM-licensed DEXRON VI is back-serviceable wherever DEXRON II or DEXRON III is recommended, so any licensed DEXRON VI fluid is a correct fill. A DEXRON III-type fluid is also acceptable. Do not use Type F, which is a Ford specification.

How many quarts does a TH350 hold?

It depends on what is empty. GM lists about 2-1/2 quarts to refill after draining the stock pan. TCI lists the transmission with a stock pan at 4 quarts without the converter, and a 12-inch converter adds about 4 more. A completely dry unit and converter takes roughly 8 quarts plus the cooler and lines, so finish every fill by the dipstick.

How much fluid does a TH350 torque converter hold?

Per TCI's converter chart, a new empty converter holds about 4 quarts at 12 inches, 3.5 at 11 inches, 3 at 10 inches and 2.5 at 9 inches. A converter that has been run before will still have some fluid in it. Always pre-fill a new converter before installing it.

Can I use DEXRON VI in an old TH350?

Yes. DEXRON VI is GM's back-service fluid for earlier DEXRON transmissions, and fluid makers like Valvoline state it can be used wherever DEXRON II or III is recommended. It is thinner when new than the old DEXRON II, but it is much more shear-stable, so it holds its viscosity over the life of the fill.

How do I check the fluid level on a TH350?

With the engine running, the shifter in Park and the vehicle level. Cool fluid should read 1/8 to 3/8 inch below ADD, warm fluid near ADD, and hot fluid between ADD and FULL. It takes only one pint to go from ADD to FULL, so add in small amounts and avoid overfilling.