Transmission Failure Linked to Faulty Oil Cooler System

I had a similar issue with my 2009 Acadia with a 3.6L engine. As someone with moderate experience working on cars, I can tell your symptoms sound very familiar, especially the transmission behavior and warning lights. In my case, the radiator coolant was mixing with transmission fluid due to a failing connection between the transmission cooler lines and radiator. The leak detection process revealed damaged O-rings and corroded fittings where the lines connect. When the cooling system loses pressure, it definitely causes the transmission to act up exactly as you described. My workshop found the cable connector was completely worn, letting transmission fluid leak into the coolant. They replaced the connector assembly and fittings for 95 Euro, which solved both the cooling system issue and transmission problems. Luckily I caught it before any major transmission damage occurred. To better assist, could you share: Current mileage, Any visible leaks under the car, Color of your transmission fluid, Whether the car overheating light comes on, If you notice any sweet smell from the engine bay This information would help determine if you are dealing with the same root cause. Quick action is important here, continuing to drive with these symptoms risks serious transmission damage.

Thanks for your reply. My current mileage is 66044 KM and my last service was just 2 weeks ago. After reading your experience, I checked under the car and found a small puddle with pinkish fluid that seems to be a mix of radiator coolant and transmission fluid. The car overheating warning hasnt activated yet but the grinding noise in the transmission is getting worse. The pressure gauge test at home showed the radiator pressure is much lower than spec. Will get it to the shop first thing tomorrow since driving with a compromised cooling system could lead to complete transmission failure. Really hoping its just the connection points and cooler lines rather than internal transmission damage.

Thanks for the additional details. Your symptoms match my Acadia case even closer than I initially thought. That pinkish fluid is a telltale sign of coolant mixing with transmission fluid through failed radiator cooler lines, exactly what I experienced. The grinding noise getting worse combined with low radiator pressure strongly suggests the cooling system issue is already affecting transmission operation. The good news is you caught it relatively early at 66044 KM, my transmission started showing these symptoms around 70000 KM. A radiator repair focusing on the transmission cooler section will likely resolve your issue. My mechanic pressure tested the entire cooling system and found multiple points where the coolant was escaping. The transmission recovered fully once they fixed the leaks and replaced the contaminated fluids. Key repairs in my case included: New transmission cooler line fittings, Replacement of degraded O-rings, Fresh radiator coolant, Complete transmission fluid flush, New transmission filter The total repair cost was around 450 Euro and prevented what could have been a 3000 Euro+ transmission replacement. Would recommend having your shop do a complete cooling system pressure test to identify all potential leak points while they have it apart.

Thanks for all the information shared. Seeing how similar your symptoms were to mine gives me more confidence about the repair path forward. The pinkish puddle and failing pressure test definitely point to the same radiator coolant and transmission fluid mixing issue you experienced. Good to hear your transmission fully recovered after the cooling system repairs. Will make sure the shop checks all those components, especially the transmission cooler lines, fittings and O-rings. The cooling system pressure test should reveal if I have any additional leak points. Catching this before major transmission damage occurred will hopefully keep my repair costs closer to the 450 Euro range rather than facing a full transmission replacement. Will update once the shop completes their diagnosis, but feeling more optimistic now that I better understand the connection between the cooling system failure and transmission problems.