Coolant in transmission?

Hey all,
2008 Tundra 5.7 V8 with the tow package 161k miles
Just bought this from auction and I'm going through all the fluids and when I drained the transmission fluid it had the same color as strawberry milk. I pulled the pan down and it seems like there was coolant that mixed with the transmission fluid. I thought the transmission cooler was separate from the cooling system, so I'm not sure how coolant made its way into the transmission. What could have caused this and how should I go about solving it along with getting all of this mixture out of the transmission? Doesn't seem like it was running like this for too long because the magnets aren't filled with anything more than expected.
Any helpful input is appreciated, thanks!

 

The transmission cooler depends, there's an external cooler and there's one that runs the cooler integrated into the top of the radiator. If you pop the hood on the passenger side behind the grille you should see either a big brick of a cooler or two hoses running up to the top of the radiator. That could be an issue. Another spot is the brick that bolts to the transmission (passenger side transmission, big round hockey puck sized thing) has coolant lines that run to it, frankly not sure what they're for and I don't think the coolant from that puck actually runs into the transmission (I thought it was just to activate the trans thermostat or something) but that could conceivably start leaking and mix though seems unlikely.

I bet your trans cooler is integral to the radiator and that's the issue. If that is, I would swap the radiator out and change the trans fluid. There's a few methods, the most common is to drain the pan, refill the pan, and then run it a bit and repeat that process. Another method you can find videos of is to take the trans cooler line and run it into a 5 gallon bucket so all the fluid gets pumped out of the transmission, and then continually refill the pan so none of the old and new fluids mix which is the downside of the drain and fill method. I wouldn't be overly worried personally, throw some fresh fluid in and fix the leak and send it.

 

It has the external cooler

 

The one that's a big brick cooler on the side of the grille?

In that case I think it'd have to be the puck then, I don't know where else coolant gets near the transmission.

 

Pink Milkshake is a big problem that sometimes repeated drain-fills (use cheap fluid for first few) as snivilous said resolves. Big known problem on T4R.org and most recommend a new radiator every 10 yrs for those type models.

I guess the later Toyota big truck designs replaced the upper trans cooler in radiator idea with just going straight off the heater core hoses and back to the puck? That is how my '15 sequandra is put together - don't ask me how I know.