Coolant got mixed in transmission fluid
 

I poured coolant into the engine, then transmission fluid starting leaking from what seemed like nowhere. I started the car and coolant reservoir became pink and began foaming.

I don't know how this happned, now I have to do a coolant and transmission fluid change again.

Honestly don't know what to do with myself at this point. Maybe owning this thing, is too far over my head.

Transmission is presently designating. I quit.

Would bet your transmission cooler heat exchange pipe in the bottom of the radiator has a leak in it.

Father why on earth did you pour coolant in to the engine ?
Do you mean the radiator ?
Only way water can get in the engine is if the auto box cooler pies inside the radiator are leaking coolant in to the transmission . This mixture in turn will end up in the coolant over flow tank. A flush is needed after you find out just what as gone wrong , and then it may have done damage to the auto transmission .

I poured it inside the upper radiator hose.
Well, at least I didn't drive the car car but, that probably doesn't matter, even at a standstill the damage is probably done.

Time to replace the radiator and flush everything

Do I have to bring it to a repair shop (tow it) to flush the transmission fluid?
Or can this been done at home?

What you can be really discouraging but since you didn't drive the car with this condition, you may have caught it in time.
If you have drained the coolant right away, drop the transmission pan. The water and tranny fluid should still be separated. In fact, you may be really lucky and there is no trace.

As the others have said, drain the transmission NOW. Since it wasn't driven, you should be ok.

The transmission cooler in the bottom tank of the radiator is bad. Is this the replacement radiator? If so I'd be filing for a refund!

Regarding the questions about filling the engine with coolant - I do the same thing. If you don't, the engine block has to fill through the bleed port on the thermostat and it takes HOURS. Given the tendency for cracked or warped heads on the 603, there's a 0% chance I'm gonna run it until the thermostat opens. Filling the block helps get the coolant circulating much faster and air bled quicker.

It's too late, the dropped the tanny pan and it was already mixed up.

So now what?

Put fresh fluid in, flush it refill and hope for the best. Perhaps no damage.

ok, getting a new radiator will probably come, months from now, unfortunately.

But the part I still don't understand is when I filled with coolant, transmission fluid starting leaking out the rear of the transmission. I didn't even start the car when it was happening.

I thought I it was from the small spill I made but it eventually turned into a huge puddle.

Don't let it sit. Find/fix the problem, drain the converter too, service it and you may be fine.

Good luck and keep us posted!!!

300SDL radiator is NLA.

You filled the old radiator? I thought it is damaged by the clutch fan. If you did fill the damaged radiator then probably the coolant compartment and the transmission fluid compartment, below the radiator, is breached. Coolant drain out from the rear of tranny. I feel for you, the SDL changed from a daily driver to crap in a few days.

Father ...,

I can second what others are saying here - I recently replaced my radiator for precisely this reason; an intermixing of coolant with trans oil.

Caught it quickly. Replaced radiator - and trans cooler lines; these were due for replacement anyway...

Dropped trans pan, flushed trans (twice so far, with filter changes). In my view, dropping the trans pan is essential, as water will tend to settle there - below the oil, obviously.

Car is running great since; I'm hoping I just got lucky. Hope you will, too!