Here's what's happening and what you should do:
* The Problem: The most likely culprit is a cracked or ruptured transmission cooler within the radiator. This allows transmission fluid to enter the coolant system. Less likely, but still possible, is a problem with the transmission cooler lines themselves. A catastrophic failure within the transmission could *also* lead to fluid mixing, but that's less likely to present primarily as a leak into the radiator.
* Symptoms: Besides the leak itself, you might also notice:
* Pinkish or brownish coolant: Transmission fluid is typically red or brown, contaminating the coolant and changing its color.
* Slipping transmission: Contaminated transmission fluid will not lubricate properly, leading to transmission problems.
* Overheating: The contaminated coolant won't cool the engine as efficiently.
* Low transmission fluid: You'll notice a significant decrease in transmission fluid level.
* Transmission fluid smell in the coolant reservoir: A distinctive burnt transmission fluid odor may be present.
* What to do:
1. STOP DRIVING IMMEDIATELY: Continuing to drive with mixed fluids will severely damage both your transmission and engine.
2. Have it towed: Don't attempt to drive the vehicle. The damage could worsen significantly.
3. Professional repair: This is not a DIY repair. You'll need a mechanic to diagnose the exact cause (radiator, cooler lines, or transmission) and perform the necessary repairs. This likely involves replacing the radiator and possibly flushing both the transmission and cooling systems. The transmission may also require servicing or repair depending on the extent of contamination.
Cost: Repairs can be expensive, ranging from a few hundred dollars for a radiator replacement to thousands if the transmission needs significant work. The sooner you address this issue, the less expensive the repair is likely to be. Delaying the repair will almost certainly increase the cost substantially.
