Fun With Transmissions - June - 2016

Checking the Fluid: Is It that Big of a Deal?

Winter has past and all eyes are looking toward the changing seasons, the days getting longer, and summertime adventures.

Your customers depend on you to take care of their vehicles so they don’t have worry about their cars when they’re away on a trip. Summer is fast approaching and your customers, just like you, are turning their eyes toward the open road for summer adventures.

Most folks know that, before hitting the road, it’s always a good idea to lift the hood and check the fluids to reduce the chances of a breakdown. Your customer may roll up in his 2011 Malibu with a 2.4L engine and a 6T40E transaxle, and ask to have his trans fluid checked. Now this may not seem like a big a deal at first… until you realize that the 6T40E doesn’t have a dipstick.

Here’s the factory procedure for checking the fluid in a 6T40E transaxle:

Transmission Fluid Level and Condition Check

CAUTION: Only use Dexron-VI transmission fluid in these transmissions; using the wrong fluid may cause internal transmission damage. Your first step should always be to make sure there’s enough fluid to run the vehicle without damaging the transmission.

With the engine off and the transmission fluid temperature at around 20º–25ºC (70º–75ºF) make sure there’s enough fluid in the transaxle to drip out the fluid level hole.

That guarantees there’s enough fluid in the sump to fill the components once you start the engine.

Non Dipstick Level Checking Procedure

  1. Start the engine.
  2. Apply the brake pedal and move the shift lever through the gears, pausing for about three seconds in each range. Then move the shift lever back to park (P).
  3. Let the engine idle for at least three minutes to allow any fluid foaming to dissipate and the fluid level to stabilize.
  4. Release the brake pedal.
    CAUTION: Always check the transmission fluid level with the transmission fluid temperature (TFT) showing 85º–95°C (185º–205ºF). If the TFT isn’t between these temperatures, operate the vehicle or allow the fluid to cool as required. Setting the fluid level with the TFT outside this temperature range will leave you with an under- or overfilled transmission.
  5. Keep the engine running and observe the transmission fluid temperature (TFT) using the Driver Information Center or a scan tool.
  6. Raise the vehicle to access to the oil level set plug (figure 1). The vehicle must be level, with the engine running and the shift lever in park.
  7. With the engine idling, remove the oil level set plug. Allow any excess fluid to drain.
    • If the fluid flows at a steady stream, let it continue to drain until it slows to a drip.
    • If no fluid comes out, add fluid until it begins to drip out.
  8. Inspect the fluid. The fluid should be red or dark brown.
    • If the fluid is very dark or black and smells burnt, look for metal particles or debris. A small amount of friction material is normal. If you see large pieces or metal particles, flush the oil cooler and cooler lines and overhaul the transmission. If there are no signs of internal damage, replace the fluid, repair the oil cooler, and flush the cooler lines.
    • If the fluid is cloudy or milky, check for engine coolant or water contamination.
  9. Inspect for external leaks.
  10. After changing the fluid, reset the transmission oil life monitor, if applicable.

That’s all there is to it: the proper way to inspect the fluid level and condition on this transmission. There are no shortcuts for checking the fluid level; shortcuts can deliver an improper fluid check and give you false readings.

You may think that we’re making a mountain out of a molehill by going so far into the proper way to check fluid level. Let’s face it: You’ve been doing this for years and figure checking the fluid level is simple, right? Maybe; maybe not.

Not too long ago I had a conversation with a longtime rebuilder and good friend of mine, Ricky (name used with his permission).

Ricky was working on a 2011 Chevy Malibu 2.4L. He had the unit on the bench and he couldn’t find anything wrong with it. He said the car came in with delayed engagements when warm. Of course my first question was, “how did you check the fluid?”

According to Ricky, “We put the unit up into the air; my R&R guy pulled the plug and oil came out of the inspection hole. At that point we knew it was full and that something must be wrong inside.”

If only it were that simple. Let’s look at what happens when the 6T40E reaches operating temperature:

This unit has a fluid level control valve (figure 2). It’s a plastic pipe with a thermal element attached to a trap door, which is mounted to the case. It’s designed to control the fluid level in the side cover (figure 3).

When the ATF is cold, the thermal element is open so oil flows into the side cover area and back into the sump. When the fluid heats up to about 50ºC (120ºF) the thermal element closes the trap door and the side cover fills to the top of the fluid level control valve pipe (figure 4).

That’s why you get a false fluid reading when the unit’s cold. You remove the fluid level plug, see oil coming out, and think the level’s okay. It’s actually low, which is what caused the delayed engagement.

If you fill these units when they’re too cold, you run the risk of overfilling. As the fluid heats up, it expands and may take the fluid level way over the fill mark. This can cause a number of issues, such as blowing fluid out the vent, aerating or foaming, and overheating. The fluid can get so hot that it melts most, if not all, of the plastic in the unit (figure 5; a 6F35N from a late model Ford Flex).

Checking the fluid is necessary to take care of your customers and keep you from making an incorrect and costly repair. When your diagnosis is spot on, your customers are taken care of, and you can be sure to have fun with transmissions!