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Check transmission fluid level on sealed transmission

How to check transmission fluid level on a sealed transmission

Car makers eliminate the transmission dipstick many years ago. These newer transmissions are referred to as “sealed transmissions.” They’re not really sealed, but the design makes it much harder for the average DIYer to check transmission fluid level on a sealed transmission. But it can be done. Here’s how.

What is a sealed transmission?

Car makers eliminated the transmission dipstick for many reasons. First, DIYers were often overfilling their transmissions because they checked the fluid when it was cold, found it low and added more fluid. Once the fluid heated up, it was overfilled. When you overfill a transmission, the gears whip air into the fluid, causing it to foam. Foamed oil doesn’t cool metal parts and it doesn’t do a good job of lubricating, so those transmission failed early.

Next, DIYers often added the wrong type of fluid. If an engine runs dangerously low on motor oil, adding the wrong oil is still better than running with low oil. Not true with a transmission. Adding the wrong oil can cause all kinds of shifting and accelerated wear problems. Some of those problems don’t go away even if you flush out the wrong fluid.

So car makers designed transmissions with a fill plug and a drain plug. They added a seal tab over the fill plug with a printed warning to scare off DIYers. They simply don’t want you screwed around with it unless you know what you’re doing.

How to check transmission fluid level on a sealed transmission?

It’s easy. First, you get a hold of a shop manual. The checking procedure and plug locations are different for every year, make, model and transmission. Plus, the fluid requirements are different. So the lesson here is: Do NOT attempt this without a manual!  Don’t have a pro grade shop manual? Call your local library and ask if they have online access to Alldata, Mitchell or Chilton. If so, print out the procedure, along with fluid type and drain/fill plug torque settings.

Transmission fluid MUST be at the recommended temperature before checking

Yes, you read that correctly. This is what messes up most DIYers. Since you have to access the fill and drain plugs from under the vehicle, this means you may have to let the transmission cool before you crawl under to check the fluid. So you can’t drive it onto ramps and then immediately crawl under and check the fluid. Plus, most shop manuals state that you must check the fluid when the vehicle is level, which means you can’t use ramps!

The GM 4T45-E transmission is a perfect example. The manual states that the fluid must be below 104°F for proper level checking. If you check this transmission when it’s hot, the expanded fluid will spill out of the check plug hole and the transmission will be low of fluid if you immediately reinstall the plug!

Many transmissions must be checked at temps between 68°F to 130°F, so some must be driven and warmed up, while others must be left to cool down.

• The shop manual instructions for checking fluid on GM’s 4T40-E and 4T45-E transmission is two pages long.

The shop manual instructions for checking fluid on Toyotas AB60E and AB60F transmissions is 14 pages long. You’ll need Toyota special service tool #00002-11100-02 to check and fill these transmissions. Fluid temperature must be within the 115°F to 133°F range for an accurate read.

How to check transmission fluid temperature?

Most shop manuals want you to check transmission fluid temperature from a scan tool. If you don’t have a scan tool, you’ll need a digital kitchen thermometer with a long probe.

Where are the check and fill plugs?

It’s all in the manual. DON’T GUESS

How to add or refill a sealed transmission. Some transmission

GM transmission check plug

require special fill tools or funnels. Trust me, you cannot do this right without the proper tools.

For more information on checking transmission fluid levels see this post on Bumper.com

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat


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