How Coolant and Transmission Fluid Mix, How It Affects The Vehicle, and What Can Be Done

In this video I'll go over how transmission fluid can enter the cooling system and/ or how coolant can enter the transmission fluid. I'll also go over how this negatively affects both the cooling system and the transmission. I then discuss what can be done about this issue.
A failure such as this is either caused by someone adding the wrong fluid to the wrong system or by a faulty transmission fluid cooler. And while people do add the wrong fluid to the wrong system it's far more likely that this is caused by a faulty cooler. A leak develops in the cooler allowing either transmission fluid to enter the cooling system and/ or coolant to enter the transmission.
This truly messes up a bunch of stuff. In the cooling system all of the rubber can be ruined by transmission fluid. It can also affect the cooling systems ability to properly cool the engine. If coolant gets into the transmission it can ruin the clutch packs and potentially the whole transmission. Usually a rebuild or a transmission replacement is needed. **If the transmission is replaced or rebuilt due to this then it is recommended to flush the cooler lines to the transmission to remove any coolant so that the new transmission is not affected.**
Of course, to repair this, the transmission fluid cooler will have to be replaced. If the cooler is internal to the radiator then the radiator will have to be replaced. If transmission fluid entered the cooling system then the cooling system will need to be thoroughly flushed out until there is no more transmission fluid in the cooling system. I'd also recommend replacing all the rubber components in the system. If coolant has gotten into the transmission it is likely the transmission will have to be rebuilt or replaced. However, It's worth a try to do a thorough transmission fluid flush with a filter replacement. (this may take several dozen quarts of fluid to do properly.)
Note: this video is superficial in nature and cannot apply to all vehicles out there. A lot of the information given in the video is a matter of opinion and may not be best for your vehicle given factors unknown. Do your own research.
Images shown in video depict not only contaminated fluid but also uncontaminated fluid. Contaminated fluid with have a "milky", thick, opaque, look to it. Some coolants are red or orange. Red and orange coolant is supposed to be red and orange. But when it gets contaminated with transmission fluid it becomes "milky" and thick. Also, most transmission fluids are red or some shade of red. This too will become "milky" and thick when coolant is mixed in with it. In both cases, with the coolant and transmission fluid, the severity of contamination may vary.
GENERAL DISCLAIMER
Barbour's Auto Help is not responsible for any damage or personal injury incurred in the process of performing any auto repairs done by you the viewer. Automotive repair is extremely dangerous. Repair your vehicle at your own risk. It is the viewers responsibility to verify all information and procedures as outlined in YOUR REPAIR MANUAL AND OWNERS MANUAL FOR YOUR VEHICLE. Owning and using a repair manual suited for your vehicle is essential for correctly and safely performing ANY repair to your vehicle. Always wear safety glasses and protective gloves and heed all instructions for use applicable to any piece of equipment you may use. Due to circumstances out of the control of Barbour's Auto Help, Barbour's Auto Help makes no guarantee that by the use of the information given in this video a quality repair will be made. Barbour's Auto Help makes no guarantee that the information provided is totally complete, synchronized and accurate. Verify everything using an appropriate repair manual.
Repair your vehicle at your own risk! Barbour's auto help does not guarantee a proper repair using these techniques.

[@maskerade81]

Thank you for this very well and easily explained of what is happening and the future of parts. I unfortunately have both issues. I bought a used 2005 Toyota Sequoia and now I have to get rebuild the transmission before it fails completely.

[@BarboursAutoHelp]

Darn it!

[@Jackiegirlone]

Wow, what a great communicator you are, this was very helpful

[@siddjay2855]

This became a very helpful video in just 1m & 27secs.. awesome!

[@BarboursAutoHelp]

Glad it was helpful!

[@pistolasnine8389]

Thank you so much! My car just had this issue, coolant mixed into the transmission....up for new transmission

[@connerdux8207]

Thank you for this video, went to take my 1979 gmc for a cruise and popped the rad cap to find a pink mix , glad I found that before driving cause I have to drive to Ontario with it

[@AXNJXN1]

Excellent information!!

[@jacobclark89]

Good point , changing all the rubber stuff .

[@daltoncastro5012]

This video saved me from doing head gaskets on my 3100 Buick

[@jorgeandresgacharna7461]

Thanks for that good explanation.

[@JeffKendallWeed]

Great video, nice work man. Helping a friend assess if she should fix coolant in trans/coolant in oil in a 200k CRV. Leaning toward letting the insurance co having the car!

[@patricwilliams9054]

Thanks so much! GREAT VIDEO AND INFO 🤝

[@BarboursAutoHelp]

Glad it was helpful!

[@teondrebrown1733]

Great video 👍👍

[@king_cobra5492]

great explanation. thanks

[@NaaLaughMuzik]

Thanks for the knowledge

[@BarboursAutoHelp]

My pleasure

[@Terry1212]

Automotive Engineers: "Hey let's put the transmission cooler inside the radiator so that if it fails the coolant can mix with the transmission fluid". Genius!

[@firdausravindar977]

Thank you very much for this beneficial video on auto transmission mechanics.

[@BarboursAutoHelp]

You are welcome

[@daveshanton485]

Thanks for the informational video! I have a pink milkshake coming out of my 84 Chevy Caprice radiator. Thanks for the words of caution on what damage can be done to both systems.

[@chrisharm6242]

Had this happen to my 2017 Tacoma, it’s in the shop now, looks like warranty is picking it up!

[@Braulio0511]

This happen on my isuzu box truck, had to replace radiator and transmission . And replace both upper and lower radiator hoses.

[@FusionDeveloper]

I just realized, since there are transmission lines running to my radiator, then that means there is a chance that a busted radiator, could potentially mess with your transmission too.

[@johnwagner4559]

That is a mess! Good information! TY I wouldn't recommend a trans FLUSH.... That can destroy the transmission as you know. I myself would service the transmission now, then again a few weeks later.

[@BarboursAutoHelp]

Hey thanks for commenting, John! Yea, I'm not a big fan of flushing the fluid either. But, concidering the factors at play, in my opinion it's best. But, I tatally understand where you are coming from. A lot of really good techs would disagree with me on some things.

[@zombiek1ller616]

I have the trans oil in my radiator but am not sure how it happened I just replaced my water pump started it up an the radiator spewed out the red stuff from the radiator cap( no leak is found)

[@keving52002]

Does anyone know if there are aftermarket radiators that have solved this problem ,with better materials use?

[@billymiller9809]

I don't normally comment on videos but great video

[@BarboursAutoHelp]

I appreciate that

[@jodo8639]

You are the man

[@aswan5086]

Whats is the amount of water that got into atf is little? Will it still hv milkshake colour?

[@Ghost0104]

Is it possible non of those options to be the cause of a bad transmission cooler could it just be clogged. Say if your line keeps popping off the same one everytime? HELLLPPPPP!!!!!

[@mezosaad5907]

thank you so much

[@BarboursAutoHelp]

You're welcome!

[@maingun07]

On my own vehicles, I've been lucky and never had that happen although on my diesel pickup I did have an engine oil cooler fail. That took 11 flushes before I was satisfied. However, I have had my friends' bring me their cars with bad trans coolers. In only one case did I see evidence of coolant in the trans and she decided to junk that high mileage car and get a new one rather than go through the expense and headache of having the trans replaced.

[@BarboursAutoHelp]

Good to hear from you, Maingun07. Thanks for sharing your experience.

[@arianabedi9552]

I’ve had my radiator blow and cause my transmission to lose 4/7 gears completely. Re did the whole radiator first was flushed over 5 times and re hosed then ordered a used transmission which I’m still waiting for. Should I be doing anything else for extra safety before I get my used one installed?

[@BarboursAutoHelp]

Did you already flush the transmission and lines? If not, I would flush the cooler lines to the transmission to get any coolant out that may be inside them. You don't want any water in the new, "used", transmission.

[@hellofromgatsville8]

Accidentally put transmission fluid in my coolant reservoir. Literally thought it where you put the transmission fluid. My vehicle takes dexron 6 transmission fluid and I was low so.... And it even said dexron on the coolant reservoir cap. I put almost half a quart in. Any advice? I'm thinking about getting a coolant flush. Also wow. Who's idea was it to put transmission fluid where the dipstick is? We all learned that you don't put oil into the oil dipstick, it has its own cap you take off and fill it up in. Wow.

[@BarboursAutoHelp]

Well, how long did you drive with it like that and did it get into the radiator?

[@12vLife]

My fault and stupidity, but battery acid leaked on to my transmission and my van would not start. I used a garden hose to wash off the acid and towed it to my dealership who said the acid had burnt through some connector pins causing electrical problems, but that also my transmission had water in it and showed me a picture from the drain plug (no dip stick). The van has never been near deep water and was otherwise was driving fine before the starting issue so I am assuming I caused this with the garden hose. This was 7 days ago and the van has not been started since the hose incident. What are the chances water might have entered via a hose from the top and be visible from the drain plug so quickly? Any chance I can still flush this water and not require a rebuild? Incidentally, I frequently would long idle my van while parked. It's never overheated, but what are the chances maybe that water entered from the radiator (transmission cooler) instead and the dealership missed it? Can this be proven conclusively?

[@BarboursAutoHelp]

That's a pickle of a situation. I'm really not sure how to answer that safely. First, I'd say it's best to listen to the tech that has actually looked at the vehicle. I don't know if they missed anything. It's always a possibility. (we are human). But, I'm wondering how water got in. Your vent is supposed to be designed to keep water out. If the vehicle had been submerged that's one thing, but you just sprayed it. Hmm.... You could take a gamble and do a really good flush on it and find out if it needs to be rebuilt when it fails down the road. (May fail under the worst of circumstances)

[@BarboursAutoHelp]

Has the dealer performed a pressure test on the cooling system. Usually if you have a leak, internally or externally, the pressure will drop.

[@12vLife]

@@BarboursAutoHelp Thanks. To my knowledge no pressure test done. Dealer also acknowledge chances of water from a quick hose wash off are very unlikely. they are basically saying this car must have been under water, but I know for sure it has not been. I am wondering if can get a sample of the fluid and test it.

[@12vLife]

@@BarboursAutoHelp Dealer said for sure it had no coolant in the transmission and that it's not possible in these vans.. not sure. . I just towed the van home removed the battery, the rusted out tray and cleaned it up. There is definitely water in the transmission, but I am wondering if it go in through this hole?.. it would seem so, but the the dealership did not think so.. photos.app.goo.gl/Rj5XyTb9f8QZ3cDX6

[@BarboursAutoHelp]

@@12vLife Holy cow! Yea, if that hole was there when you sprayed it then I'd say that's probably how it got in. lol That hole aint aposed to be there. I had no idea you had a hole in it. (I'm assuming that is the top of the trany and I'm looking into the trany at the valve body. Not sure what angle this is and I'm not that familiar with that trany.) The color of the fluid doesn't lead me to believe that coolant is in there. It looks like water. I'm so sorry, NoSunBeach. Maybe a flush and fixing the hole will get you going. Actually, If it hasn't been started you may want to start by draining the fluid first and then flushing repeatedly. You gotta fix that hole though. I hope you get around the rebuild. Good luck to you!

[@wendelfears1027]

If you don't all the change outs. You just end up doing it later down the road.

[@D4x4Bronc]

did you really scratch the ford symbol off your ranger steering wheel :S

[@garysuarez9614]

That looks truly horrifying.

[@BarboursAutoHelp]

It is absolutely horrifying.... Not a good place to be.

[@FusionDeveloper]

I wish draining gas out of a car to clean it out, was as easy as draining a radiator.

[@ivanmuniz492]

I guess the truth hurts sometimes.

[@alfredolopez8352]

Snoop Dogg talking

[@BarboursAutoHelp]

Fo shizzle!