A transmission fluid leak usually shows up as reddish or brown oily drops under the middle of the vehicle, or toward the front on many front-wheel-drive cars. The most common sources are the pan gasket, the drain plug, the cooler lines and their fittings, and the seals where shafts leave the case. Find the source and fix it early: a transmission that runs low on fluid slips, overheats and can be damaged quickly.
Is it transmission fluid? How to tell leaks apart
| Fluid | Color and feel | Usual location |
|---|---|---|
| Transmission fluid | Red to brown, oily, thin | Under the middle of the car, or front on many FWD cars |
| Engine oil | Amber to black, slick | Under the engine |
| Coolant | Green, orange, pink or blue; watery, sweet smell | Front of the car, around the radiator and hoses |
| Power steering fluid | Red or clear; some systems use transmission fluid | Front, near the steering pump or rack |
| Brake fluid | Clear to yellowish, slippery | Near a wheel or under the master cylinder |
A brake fluid leak is a safety problem: have it fixed before driving. To catch a slow leak, slide a piece of cardboard under the car overnight and check the color and position of the drips. See transmission fluid color for what each shade means.
Common causes of a transmission fluid leak
- Pan gasket and pan bolts: the most common source. Gaskets harden with age, and over-tightened bolts can distort the pan. A dented or cracked pan leaks too.
- Drain plug: a loose plug or a missing or reused washer.
- Cooler lines and fittings: the lines that run to the cooler in or near the radiator can rust, rub through or loosen at their fittings.
- Front pump seal: leaks between the engine and transmission, where it is easily mistaken for an engine rear main seal leak. Replacing it means removing the transmission.
- Output or tail shaft seal: at the back of the transmission where the driveshaft enters; on front-wheel-drive cars, the axle seals.
- Selector shaft, sensor and connector seals: small O-rings that harden over time.
- Overfilling or overheating: fluid can push out of the vent if the level is too high or the fluid is very hot; see transmission fluid temperature.
Can you drive with a transmission fluid leak?
A slow seep with the level still correct is not an emergency, but it should be repaired and the level watched. A leak that drops the level is different: low fluid causes slipping, delayed engagement, harsh shifts and overheating, and the damage from running low can turn a gasket repair into a transmission replacement. Check the level the way your owner’s manual describes; our guide on how to check transmission fluid covers dipstick and sealed transmissions.
How a transmission fluid leak is fixed
- Clean the area so fresh fluid shows where the leak starts; fluid runs downhill and spreads along the case.
- Repair the source: a new pan gasket or drain plug washer, a replaced cooler line or fitting, or a new seal.
- Refill with the fluid type your transmission calls for and check the level at the correct temperature.
Stop-leak additives that swell seals are at most a temporary measure and do not repair gaskets, lines or cracked parts. If the fluid is dark and smells burnt, or the transmission already slips, read transmission slipping: signs and causes before deciding on a repair.
When replacement makes more sense
If a long-running leak has already damaged the transmission, compare the repair with a replacement unit. We carry automatic transmissions for Chevy, GMC, Ford and Dodge/Ram trucks and cars, listed by transmission code on our transmissions page; what transmission do I have? helps you find yours, and transmission replacement cost explains what goes into the price.
More guides: car won’t move in drive · rear main seal leak · cooler lines leaking · pan gasket leak · U-joint wear and rear seal leaks.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.