How can coolant get into transmission fluid?!

[SPOW]

Just received my transmission fluid analysis back and surprised to hear they found a small amount of coolant in the fluid. This explains the poor shifting performance and quick deterioration of my transmission fluid. Can anyone suggest where these two fluids cross paths in the engine so I can replace? I see there is a transmission cooler, but I'm not sure if the fluids can mix there, if a seal was bad or a crack. 2018 CX5 2.5. Thanks for any help

 

[cz5gt]

There is a transmission oil cooler that is cooled by passing coolant through it. Probably the only place they intersect.

How many miles does your CX-5 have..? Those usually don't fail much unless they have many miles.

 

[SPOW]

Vehicle has about 90,000 miles and has once overheated due to the water pump belt breaking. Radiator has been replaced so it shouldn't be that part. I was thinking the same thing about it potentially being the transmission oil cooler, although it looks like just a big chunk of metal. Maybe it has cracked internally. Thanks for the suggestion

 

[RedBaron]

and has once overheated due to the water pump belt breaking

That's what might be called "a clue". Head warped.

 

[SPOW]

I wondered the same thing RedBaron, although this transmission fluid concern has been existing long before the vehicle overheated within the last 10,000 miles. The other question is if there is a head gasket leak, is that a place where coolant could get into the transmission fluid?

 

[N7turbo]

The other question is if there is a head gasket leak, is that a place where coolant could get into the transmission fluid?

No. Only into the engine oil.

 

[sinistriel@]

The only way other than someone putting coolant into the transmission itself is the heat exchanger intermixing. Inside the exchanger are multiple passages that have coolant, if one of those starts to leak you will get coolant in the fluid, this effects all brands that use exchangers. The problem is that any coolant inside transmission fluid damages the clutches, glycol specifically starts to attack the glue that binds the friction together.

 

[RedBaron]

I wondered the same thing RedBaron, although this transmission fluid concern has been existing long before the vehicle overheated within the last 10,000 miles. The other question is if there is a head gasket leak, is that a place where coolant could get into the transmission fluid?

No. Only into the engine oil.

Yeah, sorry, my bad. I misread 'transmission' fluid.

 

[SPOW]

Very helpful insights, thank you. I'll replace the heat exchanger and hope that the very low contamination hasn't yet destroyed my transmission clutches!

 

[sinistriel@]

I hope it works for you, 94ppm is quite high, clutch material is also hygroscopic, your best chance of saving the unit is finding someone that has a full fluid exchanger and have all the fluid changed out.