





Rear Expansion Tank/REx Coolant Reservoir Oil Contamination
Anyone dealt with this before? Took a 275 mile trip on two legs driving hwy speeds 45-75 mph. ECO Pro and Pro+. No CEL, codes, warning etc. I was very happy how the car did, I didn’t charge much and used the REx. Parked the car after the trip and moved the car yesterday and found the leak on the ground. Looked under the car and under the engine compartment. Found the leak and can see contamination in the coolant. Engine oil looks clear. I did not know about the leak, but the REx was running okay with no abnormal sounds. Held charge well.
My base search online seems to be it’s possibly the heat exchanger (oil coolant, 17-11-7-623-685) or a gasket head (seal). Won’t know until it’s diagnosed properly.
Question is, would this be considered a CARB repair? My understanding is that the coolants in the REx also cool the battery. I am in a CARB state, CA, and the car is registered in it. 2019 i3 REx w/ 62300 miles.