My friend and I were changing the oil on my 2004 LS430 and we accidentally drained the transmission while overfilling the oil. The vehicle was only moved less than 100 meters to the parking stall after completely our “procedure”. What are the odds that we messed this thing up bad?

 

You likely didn't entirely drain the transmission or else the car wouldn't move. Traditional automatics like in the LS430 work on hydraulic power which requires hydraulic oil aka transmission fluid to work. No fluid, no moving. 100 meters isn't that far to go while low on transmission fluid, not far enough to heat things up much. Maybe it caused some frothy cavitation of what fluid was left in there, but I'd say you're probably fine there regarding damaging anything.

Overfilling the oil is a different problem. Some engines do just fine with extra oil like Hondas and Ladas, while others will start to blow seals due to increased oil pressure from having too much oil. But again, 100 meters isn't that far and so the engine wasn't running very long, hopefully not long enough to blow out a seal. Otherwise the engine just cavitates the oil and makes it all frothy from the crankshaft counterweights and/or piston rods smacking into the pool of oil in the oil pan, if you filled it up far enough for that.

Explanations aside, I'd replace all of the engine oil, including drain the half-dirty oil out of the, assuming new, oil filter, and then refill the transmission to the proper level and look for any oil leaks in the next couple days/weeks. If you've got no leaks then you're probably just fine.

 

The odd that you caused any damage is low, but not zero. Whatever damage (if any) was done, it's too late to worry about it now.

I would just start over with the engine oil. Just drain it and re-fill it with new oil. If you changed the oil filter, just leave it. A 1/2 quart r so of dirty oil isn't going to matter.

Top off the transmission with Type T-IV. Avoid one size fits all ATF; just my opinion. Hopefully, you didn't put engine oil in the transmission.

 

I would not recommend using Type T-IV. The 2004-2006 use ATF WS, and there is no dipstick or easy way to fill. The fill cap is on the side of the transmission. If you're not comfortable with following the steps to check, I would recommend you have a shop that is familiar with these transmissions do the work.

 

Thanks for the correction. I missed the model year in question.

 

I've seen engines that people overfilled with literal GALLONS of oil, and then are cruising around on the street, wondering why the car a smoking before bringing it to our shop.

Although it's not harmless per se, having a TON of oil in most engines won't damage a good majority of them in short bursts, especially for such a short distance.