I had transmission fluid show up in the engine coolant reservoir of my 1999 Chevy Tahoe. I first noticed this sometime after also noticing an intermittent rattling (washboarding) which sounded like it was coming from the transmission. I made the mistake of continuing to drive, and about 25 miles later the entire transmission went out (only neutral "worked"). (BTW, the vehicle has TWO auxiliary transmission coolers in series with the cooler in the radiator.)
Different shops give me different explanations as to what happened. I'd like to get YOUR experiences/opinions!
Theory 1: The transmission was failing (possibly torque converter going bad), causing bits of metal particles and debris to plug the transmission cooler part of the radiator, which caused fluid to spill into the overflow reservoir (just how I don't know).
Theory 2: The transmission cooler in the main radiator developed a leak and allowed fluid to leak into the coolant and coolant to leak into the fluid. The coolant, once getting inside the transmission, ruined it.
Theory 3: ???
At any rate, when the transmission got rebuilt the shop also bypassed the main transmission cooler so that I am now using only the two auxiliary coolers. I am posting separately with questions about this.
I'd like to get your opinion on which theory above is most likely, but my main question is: If only the transmission cooler in the main radiator developed a leak and not the engine coolant part, then how can the transmission fluid get mixed in with the coolant? (It *did* happen -- I'm just trying to understand *how* it was possible.)
--S. Miller