Transmission fluid in antifreeze: what to do?


My friend is unemployed and has about $500 to his name. He discovered the car (a 2002 Dodge Neon with 137,000 miles) leaking antifreeze and transmission fluid on the street. Tried driving it around the block; it went into gear at first, but then locked up when he tried to put it in reverse when parking it. He opened up the radiator to find a mix of antifreeze and tranny fluid.

The car was towed to a friend’s shop, but he doesn’t do major work like trannies. At this point, he can either repair the radiator and refill fluids for $500, then perhaps find out the transmission is shot too, or what I think he should do is have it towed somewhere else where they can tell if the transmission is shot before replacing the radiator. Is this possible? Suggested courses of action? He needs the car to get to a job he was just offered and has been searching for for months. Thanks in advance!


P.S. Obviously it will take all his money (including credit on his credit cards) to do the radiator work, so he can’t afford it if that turns out to be just the beginning; he would need to find another strategy. That’s why the angst.


You have a leak between the rad and tranny cooler, you’ll need to replace the rad at the very least.

You’ll also need to drain and flush the tranny and replace the tranny filter. You might be lucky and get away with just that.

Worst case, water has blown the tranny valve block seals ~ that’s probably a new tranny.


Actually, what happens when engine coolant gets into the transmission the coolant will destroy sealing rings and will cause the clutch and band friction material to come apart. It sounds as though the radiator will need to be replaced AND the transmission disassembled completely, vatted to clean all the coolant out of it and rebuilt. He’s looking at around $2,000-$2,500 if he’s lucky.



If it was me, and I was broke, I would replace the radiator as cheaply as possible (maybe used), replace the coolant, replace the tranny fluid and filter, and hope for the best.


How does this happen and what can you do to prevent it?


“How does this happen and what can you do to prevent it?”

It happens if the transmission cooler (inside the radiator) leaks, letting the higher pressure coolant into the transmission fluid.


Examine the transmission dipstick carefully. Is there ANY SIGN of moisture or coolant in the transmission fluid?? If the answer is yes, then the car is totaled. Since the tranny “locked up”, I doubt a fluid change will help.


I would not spend one dime on it at this point. Pull the transmission dipstick and examine the fluid. If it’s blackened or resembles sour milk then you can figure the trans is trashed so the radiator is a non-issue at this point.

Considering the coolant leak, there’s a chance the locking up could be the engine either overheating or it has suffered a blown head gasket. Coolant can enter the combustion chamber(s) past a blown gasket and cause what is called “hydrolock”.

To prevent problems in the future, I would advise disconnecting the radiator trans fluid cooler completely and installing an aftermarket fluid cooler.
These can be had cheap, they’re easy to install, and worth their weight in gold. Not only do this eliminate more transmission fluid heat they also get totally rid of that leaking radiator cooler problem.
You can get a fluid cooler for anywhere from 50-75 bucks and that’s dirt cheap insurance is the way I look at it.


But there IS no transmission fluid. It all leaked out. Can’t the tranny have locked up just because all the fluid leaked out while he was going around the block?


Yes it is possible the transmission is not working due to lack of fluid, I would not assume the transmission is ruined. If he wants to try to fix it he need to get rid of the leak and replace both the coolant and transmission fluid. No one can diagnose this over the internet, he either needs to attempt to repair it, have someone diagnose it in person, or give up on the car.


The problem is that he has almost no money and needs a car to start working at a job just offered to him. The shop it’s at right now can’t diagnose the transmission. I think he should tow it to a place that can, but I need specific info to tell him where to tow it - will a dealership be able to tell if the tranny is shot without taking it apart?


Can they temporarily bypass the transmission cooler with the leak, refill the transmission and see if it works at all? That might give him some indication of the size (cost) of the problem.


I would suggest removing the transmission dipstick and examining it. If the dipstick is blackened, the trans is toast.
If the dipstick has a burned smell, the trans is toast.

If the engine was operated with no fluid in the trans as you say, the trans is toast.

Considering the radiator problem, more than likely a trans wipeout, and even a potential engine problem, the car may be history. No way is it worth sinking 500 into just for starters.
He’s better off doing some footwork and finding another car. It may be an older one, bland and boring, and even downright ugly, but the object is getting from Point A to Point B.

Your friend is partly to blame for this. One does NOT continue to operate any vehicle that is suffering a bad coolant, trans fluid, or engine oil leak. If one chooses to continue on while praying then bad things will probably happen in spite of asking for divine intervention.


When you say “continue to operate,” he refilled the transmission fluid and then drove around the block. That’s not the most irresponsible action, I would say. Just a brief test, which showed the transmission fluid was leaking out very quickly. Please note that I’m asking for help (and most people are being most helpful, thank you!!!), not for blame.

Just spoke to him again - the dipstick looks clean, shiny, good as new. Is this a good sign, then?


Where is the fluid leaking out, is it leaking into the coolant system or is it leaking someplace else?

Was is shifting correctly when it had fluid?


It’s leaking out the bottom of the radiator, which was filled with a mix of coolant and tranny fluid.

It was shifting correctly when it had fluid.

Thanks for asking. :slight_smile:

He told me now that he cut a deal where the radiator is being replaced, and if the transmission doesn’t work after that, he doesn’t have to pay for the repair… good deal!


It sounds like he needs to replace the radiator/transmission cooler to get rid of the leak and change both the transmission fluid and coolant to make sure they are no longer mixed. With luck, he didn’t do any real damage to the transmission. Don’t drive it any more with the possibility of coolant in the transmission. Call local junk yards to find a good used radiator.


“He told me now that he cut a deal where the radiator is being replaced, and if the transmission doesn’t work after that, he doesn’t have to pay for the repair… good deal!”

Good deal, hope it works out.


Is the transmission cooler a separate part from the radiator? It looks like it from a quick google search.