Transmission leaks when parked

Transmission leaks when parked — Find leak

Why a transmission leaks when parked

You drive  your vehicle and then park it. In the morning you see a puddle of transmission fluid on the ground. The reason it leaks then rather than while you’re driving is because the transmission fluid and the transmission pan and gasket heated up and then cooled down. It’s the expansion during heating and then the contraction during cooling that created the gap that allowed transmission fluid to leak out.

How to locate the source of the transmission fluid leak

You’ll need a few cans of brake cleaner to clean off the transmission pan and the transmission cooler lines. You’ll also need some baby powder.

Spray off all the oil and dirt from the bottom of the transmission. Then spray all the oil off the transmission cooler lines, output shaft seals and filler/drain ports. Dry with compressed air. Then sprinkle baby powder around the transmission pan gasket and the transmission cooling line connections.

Follow the same procedure on the engine/transmission cradle anywhere you see oil/grease buildup.

Then drive the vehicle and inspect the powdered areas. If you see fluid on the ground, follow the path of the fluid back to the starting point (air travel under the vehicle moves the leaking fluid towards the rear of the transmission).

Most transmission fluid leaks are from a leaking transmission pan gasket

Replacing the pan gasket isn’t difficult but it is messy. So you’ll need a large drain pan to catch all the fluid. You’ll also need replacement fluid, plastic gasket scrapers, brake cleaner, rags and a new gasket or RTV sealant.

How to remove a transmission pan

Using a socket and ratchet, loosen but don’t remove all the transmission pan bolts. Once all the bolts are loosened, start at one end of the pan and remove the bolts. As you remove more bolts, use a plastic scraper to break the pan gasket loose. Transmission fluid will begin to see out the pan where you’ve remove the bolts. Let it drain for a while to get the most fluid out before you remove more bolts.

Then gradually remove the rest of the bolts and remove the pan.Let the fluid drain while you prepare the pan.

Prepare the transmission pan

Scrape off the old gasket and any RTV. The mounting flanges must be clean. Do the same on the transmission mounting surfaces.

Remove all traces of gasket material, adhesive or RTV from the mounting flange. Clean the pan and magnet. Dry.

Using RTV instead of a transmission gasket

If the carmaker used RTV instead of a gasket, make sure you buy the correct gasket maker. Keep in mind that there are many options. You can buy gasket maker that needs to cure overnight before you re-fill with transmission fluid, or you can buy gasket maker that allows you to refill the transmission right away. Permatex The Right Stuff is what most shops use for transmission applications because it allows them to re-fill sooner.

See this post for instructions on how to use RTV.

How to install a transmission pan gasket

Unless otherwise stated in the instructions, transmission pan gaskets are designed to be installed DRY. Do not use gasket adhesive or RTV.

Place the gasket on the pan, install two bolts at opposite ends and finger tighten the two bolts. Then install all the rest of the bolts finger tight. Once all the bolts are installed finger tight, switch to a socket and torque wrench.

Start in the middle of the pan and tighten the bolts to manufactures specifications, alternating opposites sides out from the middle. Do NOT over-tighten. It’s easy to over-tighten, strip, and even break transmission pan bolts. You’ve been warned.

©, 2022 Rick Muscoplat